Archive for August, 2015

CircuitWorks Epoxy Overcoat CW2500

Wednesday, August 19th, 2015

Frequently Asked Questions
Circuitworks® Epoxy Overcoat, CW2500

1. What is an Epoxy Overcoat?
Circuitworks® Epoxy Overcoat is a permanent green coating formulated to protect circuit traces before being exposed to reflow conditions. It is a two component, 100% solids epoxy that is engineered specifically for high temperature resistance, used for electronic circuit and component protection. When properly cured the insulator forms a chemically inert coating that seals out moisture and environmental contaminants, minimizes thermal shock and prevents corrosion, oxidation, and abrasion. The Epoxy Overcoat easily withstands brief exposure to high temperatures found in normal wave and reflow applications.

2. What is the difference between Circuitworks® Overcoat Pen (CW3300G) and Circuitworks® Epoxy Overcoat?
Circuitworks® Overcoat Pen is a one component, acrylic-based system with fair heat resistance and satisfactory chemical
resistance. When subject to reflow conditions this material will quickly degrade. However it does have excellent electrical insulation and good abrasion resistance. Circuitworks® Overcoat Pen is primarily designed for protecting and electrically insulating circuit board traces and components, with an easy to use one component system.

Circuitworks® Epoxy Overcoat is a two component system with outstanding high temperature and chemical resistance. Abrasion
resistance is also excellent for this epoxy system. It’s the best choice for repairing the permanent solder mask/solder resist when the boards will be subject to reflow conditions. It also has outstanding dielectric properties as permanent coating for use on bare metal.

3. What is the mixing ratio?
The mixing ration is the volume of part A needed to mix with part B. This can be critical with some epoxy systems, and can be
difficult to get the exact quantities in the right ratios as 0.96:1.32 is not unusual. This epoxy system was developed to provide
easy mixing ratios, with a very forgiving cure system. The mixing ratio for the Epoxy Overcoat is 1:1, but this ratio is not critical to obtain the best electrical and protective capabilities.

4. What are the features and benefits of the Circuitworks® Epoxy

Features

• High temperature resistance
• Provides a hard, durable protective coating
• Excellent dielectric properties
• Solvent resistant
• Service temperature -55ºF/-48ºC to 600ºF/315ºC
• Meets IPC-7721.2.4.1 requirements

Benefits
• Ideal for pre-reflow solder resist repair
• Prevents corrosion, corrosion, oxidation, degradation and thermal shock
• Electrically insulative coating helps prevent electrical discharge
• Will not be removed by solvent cleaners
• Can be used in many environments
• Perfect as solder resist board repair

5. How is the Circuitworks® Epoxy Overcoat packaged?
The Epoxy Overcoat is packaged in two (one part A and one part B) easy to use syringes that hold approximately six (6) grams of
material. One syringe contains the epoxy, while the other contains the hardener. This allows you to use as little or as much material as you need.

6. What type of customers would use the Circuitworks® Epoxy Overcoat?
Customers involved in the manufacture and the rework/repair of printed circuit boards would use the Circuitworks® Epoxy Overcoat.
This would include those involved in:
• Circuit board manufacturing
• Data communications
• Aerospace industry
• Instrumentation and control manufacturing
• General maintenance repair

7. Can the Circuitworks® Epoxy Overcoat be used as an encapsulant?
Circuitworks® Epoxy Overcoat’s physical properties are very similar to epoxy encapsulants; it will work to encapsulate leads, traces
and small areas that need insulation and protection. However, the small quantity contained in each syringe does not make it an
ideal candidate for encapsulation.

8. Can the Circuitworks® Epoxy Overcoat be used as a conformal coating?
Conformal coatings are applied in thin layers onto printed circuit boards to provide environmental and mechanical protection to
components and circuitry. Even though the Circuitworks® Epoxy Overcoat can provide protection, the higher viscosity and small
quantity contained in each syringe does not make an ideal candidate for performing as a conformal coating.

9. What’s the shelf life of the Epoxy Overcoat?
The shelf life is twelve (12) months from the manufacturing date.

Chemask NA Non-Ammoniated Solder Mask

Wednesday, August 19th, 2015

Frequently Asked Questions
Chemask® NA Non-Ammoniated Solder Mask

1. What is Chemask® NA? What are its features and benefits?
Chemask® NA Non-Ammoniated Solder Masking Agent is a fast curing, peelable temporary spot mask formulated for safe use on
sensitive metals. It contains high-temperature resistant compounds that protect component-free areas during wave soldering.
Chemask® NA may also be used to protect pins, posts, contacts and edge connections in the solder reflow oven or during
conformal coating processes.

• Stable to 550°F (288°C) – withstands lead-free processing temperatures
• Ideally suited for use with gold, copper, nickel, silver and OSP finishes
• Works with both lead-free and tin/lead applications
• Phthalate-free, low toxicity and environmentally safe
• Compatible with all flux types and cleaning solvents
• Dries tack free in 15 minutes (10 mil thick application)
• Can be introduced into the pre-heat oven without being fully cured
• Removes easily by hand and leaves no residue
• Non-contaminating, non-staining and non-corrosive on all surfaces
• RoHS compliant

2. How does the new Chemask® NA compare to the latex peelable mask Chemask® CM8?
Chemask® NA is also a peelable mask and works as well as Chemask® CM8. The primary differences are that Chemask® NA does
not contain ammonia, and is therefore compatible with lead-free board finishes such as immersion silver, immersion gold, nickel,
lead-free HASL and Entek. Chemask® NA can also be used on standard tin/lead board finishes, including bare copper. Chemask®
NA will also withstand hotter processing temperatures and longer cycling times than any other mask on the market today.
Chemask® NA is not as elastic as Chemask® CM8, which tends not to be a problem with most electronic applications. For other
applications, it can be used successfully on a variety of non-porous surfaces.

3. How do I use Chemask® NA?
When applying the mask by hand using 8 oz. squeeze bottle, insure that all areas of the pre-tinned hole or pad are evenly covered
on the side to be soldered. Automatic dispensing equipment may also be used as appropriate. Chemask® NA can also be applied
using a screen or a stencil. For ease of removal, a minimum thickness of 30 mils is recommended.
Chemask® NA can go straight into the pre-heat oven of a wave soldering machine, or can go into a reflow oven 15 minutes after
application to the PCB. This mask may remain on assemblies for extended periods of time prior to or after processing.
After processing the board, Chemask® NA can be easily peeled off the board by hand or using tweezers.

4. What if I want to apply an extra thick layer of Chemask® NA to the board?
When Chemask® NA is applied in a thick application (> 1/8″), allow extra drying time or oven dry at 250ºF for 30 minutes.

5. If I put Chemask® NA into the pre-heat oven after a short 15 minute cure time, won’t
bubbles form in the mask?

No. Chemask® NA will withstand preheat temperatures without degradation or distortion of the film and will be completely cured by
the end of the processing cycle.

6. Is Chemask® NA completely non-flammable?
Yes. Chemask® NA is non-flammable and contains no flammable components.

7. Is Chemask® NA safe to use?
Yes. Chemask® NA has no strong odors, is non-toxic and, unlike competitors’ products, does not contain phthalates.

8. Is Chemask® NA RoHS compliant?
Yes. RoHS certificates are available on the Chemtronics website www.Chemtronics.com.

9. Is Chemask® NA environmentally friendly?
Yes. Chemask® NA contains no VOC’s or other harmful volatile components. After it has been cured, Chemask® NA can generally
be disposed of without any worries about hazardous waste generation.

10. How can I tell if the product I am using is Chemask® or Chemask® NA?
Chemask® NA is tinted green while the other peelable Chemask® products (Chemask®, Chemask® HV and Chemask® Lead-Free)
are pink.
11. What is the shelf life of Chemask® NA?
The shelf life is three (3) years from the manufacturing date stamped on the container.

12. What type of companies would be interested in these products?
The primary customers that use temporary solder masks are electronics manufacturers, including OEM and contract
manufacturing companies.

13. How is the product packaged?
Chemask® NA is available in two sizes:
• CNA8 8 oz. squeeze bottle packaged in 24 per case
• CNA1 1 gallon

Source: ITW Chemtronics

Are Chemtronics UltraJet Dusters ESD Safe?

Wednesday, August 19th, 2015

Are Chemtronics Ultrajet Dusters ESD Safe?
Lately I have been asked this question a lot. The answer is no and yes!!! No in that we don’t do anything specific to make it “ESD safe” ( as we do for our Freez-It Antistat) and yes, in that dusters do not generate a static charge when sprayed against a surface.

Static electricity is generated whenever two dissimilar surfaces rub against each other and then are quickly separated. Electrons will migrate from one surface to the other surface. One surface gains electrons (builds a negative electric charge) and one surface looses electrons (builds a positive electric charge). The magnitude of this effect depends on a number of factors: the speed of movement or separation between the surfaces (which relates to the kinetic energy of the molecules in the two surfaces), the relative humidity, the types of materials involved, and the characteristics and geometry of the surfaces involved.

Walk across a carpet in the winter, in a room with relatively low humidity, then touch a doorknob or another person, and you may get an uncomfortable electric shock. We’re all familiar with this occurrence of static electricity. As the soles of your shoes rub against the carpet surface your body builds up an electric charge, either positive or negative, with the carpet building up the exact opposite in charge. This is called a triboelectric charge, a static charge produced by rubbing. If the relative humidity in the room is low enough, walking speed produces enough kinetic energy (energy of motion) to cause a transfer of charge (transfer of electrons) during the collision of the molecules that make up the soles of your shoes with the molecules of the carpet’s surface. If you touch a grounded object you’ll discharge this electricity, sometimes painfully!

For an aerosol product to be rated as ESD safe the aerosol spray must generate a static charge of less than 100 volts when sprayed against a surface. In the case of a gas duster, no triboelectric charge can develop because, at normal temperatures, the
gas molecules do not develop enough energy of motion (kinetic energy) to cause a migration of electrons during collision with another surface or molecule. The amount of kinetic energy a gas molecule contains depends on its mass (weight) and its
velocity (speed). A gas molecules will be moving very fast across a stationary surface, but it has very little mass, so the energy or force with which it collides with the surface is not enough to cause a transfer of electrons between the
molecule and the surface. Therefore duster products, which emit a stream of gas molecules, could be said to be “naturally” ESD safe, in that they cannot produce a triboelectric charge.

We can even back up this claim with laboratory test data. We have a device in the lab that measures the voltage on a charged metal plate. We can set the initial charge on the plate to zero, then spray a duster directly onto the plate and note the voltage of the triboelectric charge that develops on the plate due to contact with the gas stream. In all
our tests the voltage on the plate remained at zero. This is sufficient evidence to conclude that an aerosol gas stream does not produce triboelectric charging and to qualify our dusters as ESD safe for all charge sensitive environments.

A substantial static charge can be generated when a stream of liquid passes through the components of an aerosol can. As the material stream rubs against the inside of the diptube or aerosol valve and the inner walls of the extension tube, electrons
migrate from one surface to the other surface and the material stream develops either a positive or negative triboelectric charge. Since circuit refrigerants (freezers) deliver a liquid stream of super-cold liquified gas, we have created Freez-It Anti-Stat, which has a built-in static dissipative agent.

So, to wrap-up this discussion, aerosol gas streams do not produce a build-up of static electricity when sprayed against a surface. Since aerosol dusters emit a gas stream they will not produce a build-up of static electricity on any surface they are sprayed onto, therefore they’re ESD safe.

Source: Michael Watkins, ITW Chemtronics

Chemtronics’s Coventry Swabs & Wipes FAQs

Wednesday, August 19th, 2015

Frequently Asked Questions
Coventry™ Products for Critical Environments

1. Are all of your products manufactured in a Cleanroom?
Coventry™ manufactures products in a cleanroom whenever it is necessary to meet the quality requirements of the customer. Since processing and packaging in a cleanroom can significantly increase the cost of a product, Coventry seeks to employ other contamination control strategies in our manufacturing processes. In some cases the use of a cleanroom in unavoidable. Laundered, knit polyester, or microfiber wipers are an example, where sorting, inspecting, flattening and packaging processes must be done in a cleanroom to prevent product contamination. With other products we have developed proprietary manufacturing processes that have proven effective in isolating the product and packaging.
2. What classification cleanroom are Coventry products manufactured in?
The products that are manufactured in are laundered and packaged in a class M1 cleanroom.

3. What is the difference between, cotton, foam, polyester/cellulose, polyester, and microfiber?
Except for the microfiber Cleanroom Chamois™, absorbency (cleaning ability) and cleanliness usually go in opposite directions. That is to say, very clean materials such as synthetic polyester are really not especially absorbent. Even so called ‘high-absorbency polyester’ is not very absorbent. It may be more absorbent than some other polyester, but it will not approach the absorbency of cellulose. The highly absorbent materials are usually based on natural fibers and cellulose which tends to shed particles.

4. Do you have ESD Swabs?
Yes. We have a variety of ESD-safe swabs. Our ESD swabs feature a blue (the universal color for static dissipative), solvent resistant, low contamination, dissipative handles.

5. Which are your cleanest swabs?
Our folded and wrapped polyester are the cleanest swabs in the world. Most swabs are made using some sort of a seal, which
creates edges (a high source of contamination). Our folded and wrapped polyester swabs, do not have any exposed edges thus the lowest level of contamination.

6. If I am using a solvent, which head material should I use?
Polyester and microfiber heads are generally more chemically resistant than foam heads.

7. Which swab is best for cleaning sensitive surfaces and mirrors?
Our microfiber swabs offer a chemically resistant material that is especially soft and absorbent.

8. Which swabs are best for removing flux residue from a PCB?
Our foam swabs with ESD sticks allows for high absorbency and good chemical compatibility when using IPA. If acetone were
being used, our polyester or microfiber swabs (ESD of course) would be recommended.

9. What products should I use to clean flat panel displays?
Our Microfiber sealed edge wipe is the best choice in the industry. It offers the lowest levels of particles and fibers that might cause defects in the flat panels. In addition, the high absorbency of the wipe is extremely desirable when cleaning displays.

10. Can wipers be re-laundered?
Since a used wipe will never get as clean as a new wipe, we cannot recommend the use of re-laundered wipers in critical
environments. However, the microfiber wipe has a high abrasion resistance and launders exceptionally well. As a result some
customers have had success at commercial re-laundering and re-use the microfiber wipe in not such a critical environment.

11. What is the best wipe for cleaning optics?
Our Econowipe™ is a 100% nonwoven wiper, which is excellent for optics. Because it is manufactured using high-speed jets of
water, it has extremely low levels of extractables. However some specialized coated optics might be damaged by the use of this wiper. Coventry’s™ microfiber wipe provides the lowest levels of particles and fibers for wiping glass surfaces and flat panel display
manufacturing.

12. What is the difference between a laser-edge wipe and a hot-cut edge wiper?
Coventry’s highly effective laser-edge wipes have bonded borders that seal rows of loops on the border of the knit, which produces durable and consistent fiber control suitable for class 10-100 cleanrooms. A hot edge leave loops of yarn that can break free during use and result in contamination.

Source: ITW Chemtronics

Lead Free Soder-Wick

Tuesday, August 18th, 2015

Soder-Wick® Lead-Free
1) What exactly is Soder-Wick® Lead-Free SD?
Soder-Wick® Lead-Free SD is a new desoldering braid that has been engineered specifically for optimal removal of lead-free solders, which have a much higher melting point than tin/lead solders. However, it is also effective at removing current tin/lead solders. The SD designation means that the desoldering braid is wound on a static dissipative bobbin to protect the board being reworked from a destructive static discharge.

2) What is the difference between the new Soder-Wick Lead-Free SD and other desoldering
braids like the original Soder-Wick® Rosin and Soder-Wick® No Clean?

The innovative weave of Soder-Wick® Lead-Free SD conducts heat more quickly to the solder joint so more heat energy goes where it is needed to melt the higher melting point, lead-free solders. This shortens the time it takes the solder to liquefy and shortens the overall time required to remove solder when using Soder-Wick® Lead-Free SD. Also, since more of the heat is transferred to the solder joint, Soder-Wick® Lead-Free SD alleviates some of the burden on the soldering iron. The quicker heat transfer means that the operator must also work more quickly to prevent overheating of the solder joint, pad or component. Other wick products do not conduct heat to the solder as quickly and place more emphasis on moderating the heat transfer into the joint. One additional benefit is that some users may find that they can use temperatures for lead-free desoldering similar to conventional tin/lead solders when desoldering with Soder-Wick® Lead-Free. This will reduce oxidation and increase soldering iron tip life
compared with much higher temperature applications.

The innovative weave also makes Soder-Wick® Lead-Free smoother than the current Soder-Wick® Desoldering Braid. This is done
to reduce scratching and marring pads.

Soder-Wick® Lead-Free SD employs a ‘no clean’ flux specifically formulated to tolerate the higher temperatures and poorer wetting capability of currently available lead-free solders.

3)Do I have to use Soder-Wick® Lead-Free to remove lead free solders?
No, Soder Wick® Rosin and Soder-Wick® No Clean will also effectively remove lead-free solder but they are not optimized for leadfree
solder removal. They will require
(a) a soldering iron tip that is slightly larger than the joint and desoldering braid,
(b) possibly higher temperatures, which may shorten soldering tip life and
(c) a higher power soldering iron for faster thermal recovery.Some operators may actually prefer the original Soder-Wick® products and are more comfortable adapting their technique and equipment to lead-free solders, rather than changing to the new Soder-Wick® Lead-Free.

4) Does Soder-Wick® Lead-Free remove lead containing solders effectively?
Yes, Soder-Wick® Lead-Free effectively removes conventional lead containing solders. However, operators accustomed to the original Soder-Wick® may find that the braid heats-up more quickly and must adapt their technique.

Lead Free and PCBs

Tuesday, August 18th, 2015

Printed Wiring Boards

Do the printed wiring boards have to be lead-free?
Estimates are that 60-70% of printed wiring boards are tin-lead solder coated, usually by hot air solder leveling (HASL). The solder coatings are applied to the copper surfaces of the printed wiring board to preserve solderability and protect the copper conductors from environmental corrosion. To comply with European Restriction of Hazardous Substances (RoHS) Directive 2002/95/EC, tin-lead solder cannot be used.
What lead-free finishes are alternatives for tin-lead finishes?
There are many proposed alternatives for tin-lead finishes, none performing equal to tin-lead. Changing to lead-free is not going to be as easy as just changing to another coating. Some alternatives are: •hot air solder leveling (HASL) with lead-free solder, such as tin-silver-copper, tin-silver, or tin-copper
• organic solderability preservatives (OSP) placed on the copper
• immersion tin or bismuth, applied in thin coatings of 1-2 microns, or silver coatings of less than 0.1 micron
• palladium applied electrolessly directly on the copper, or coating the copper with nickel and then palladium
• electroless nickel coated with immersion gold (ENIG)

What problems might be anticipated with lead-free printed wiring boards?
The least amount of problems would be putting no coating on the copper and trying to keep the copper surface clean and active during storage and assembly. The choice of coatings presents different problems. •Hot air solder leveling (HASL) coatings present a problem common also with tin-lead solder, i.e., non-uniform pads causing problems with placement of surface mount components. Also, the lead-free alternatives do not have the same appearance as tin-lead, generally being dull or grainy.
• Organic Solderability Preservatives (OSP) are not very heat-stable. Though barely being able to withstand one heat of soldering, the OSP coating makes soldering very difficult for a second reflow.
• Immersion tin coatings less than 1-micron directly on copper can result in decreased solderability as the copper-tin intermetallics form. This can lead to the formation of tin whiskers erupting out of the tin coating. A nickel coating under the tin can improve solderability and minimize the tin whisker formation.
• Palladium is deposited on nickel over the copper. This is an expensive coating that is used on components but not often on boards.
• Electroless nickel under immersion gold (ENIG) provides a solderable coating, but is expensive. The gold (about 0.1 micron thick) dissolves instantly in the melted solder, and soldering is done to the underlying nickel. The amount of phosphorous deposited with the nickel determines whether the soldering is going to be reliable or not.

Source: Kester Solder co.

Lead Free Component Finishes

Tuesday, August 18th, 2015

In the component finish selection avoid lead bearing finishes. The lead in the finish will dissolve into the lead-free solder. This will cause the formation of lead intermetallic phases with differing physical properties (such as expansion/contraction differences) and differing melting points. Work is ongoing to determine the long-term effects of small amounts of lead on high reliability electronics. For many consumer electronic assemblies such as mobile phones and household electronics, where the thermal cycling and condition of use are not extreme the inclusion of lead in component finishes has not demonstrated any negative characteristics to the solder joint integrity. As Japan and Europe progress with lead-free assembly numerous component finishes are already available without lead. It is important to work closely with component suppliers to insure the lead finish is lead-free compatible, the component molding plastic is able to withstand the higher temperatures associated with lead-free soldering and also the component’s reliability will not be jeopardized with the higher exposure temperatures. •Some common finishes include:
◦NiPd
◦NiPdAu
◦SnB
◦Sn
◦SnCu
◦SnAg
◦Au
◦AgPt

◦More finishes are originating from Asia
•PBGA
◦ With SnAgCu, some issues need to be investigated

•Flip Chip
◦ Patented indium alloy compatible with SnAgCu
◦ Might be exempt

•Molded Components
◦Concern about higher processing temperatures, components are available that sustain the higher soldering temperatures.

•Component Process Consideration
◦ Work closely with component suppliers
◦ Determine component lead-free finish availability
◦ Select best solderable finish and component finish shelf life
◦ Select components with compatible molded plastics and the ability to sustain the thermal requirements of the lead- free process
◦ Material handling logistics, segregate lead-free finished components from leaded components, if using both a lead-free and a leaded assembly process
◦ Insure the components and component feeders are identified as containing lead-free finishes.
◦ Train purchasing, receiving and assembly personnel on the handling procedures to avoid confusion between leaded and lead-free components during the transition stage.
◦ Identify the soldered assembly as lead-free to insure the proper rework of the lead-free components in-house and in the field.

Making Lead-free a Reality

Tuesday, August 18th, 2015

Lead-free fluxes used in solder paste, liquid flux for wave soldering, flux gels and wire solder are available today. These flux systems are designed to enhance the soldering process and are formulated to give excellent solder wetting performance with the added thermal stability of the chemistry, required with lead-free assembly. Traditional fluxes used with tin-lead alloys may not be adequate to circumvent the slower wetting of lead-free alloys and the higher temperatures normally associated with lead-free solders. Flux systems specifically formulated for lead-free soldering will require new activator packages and heat stable gelling and wetting agents to avoid solder defects. Due to the slower wetting and higher surface tension of many lead-free alloys, choosing the right flux for lead-free soldering will prevent the increase of solder defects and greatly assist in maintaining production yields. Typical defects, which can show an increase when transitioning to lead-free assembly are detailed below. These defects can be eliminated with proper flux selection and process control.

• Potential Defect Increase – Lead-free SMT Assembly
Bridging – Paste with poor hot slump behavior
Solder balls – Paste with poor slump properties
Tombstoning – Thermal differences across board
Non-wetting – Excessive preheating or inadequate flux activity
Poor wetting – Poor flux activity or excessive preheating
Solder Voids – Thermal profile too low, or inadequate flux chemistry
Solder beading – Paste with poor hot slump or excessive preheating
Potential Defects Increase – Lead-free Wave Soldering
Bridging – Flux deactivation during preheating or solder contact
Icicling – Flux too low in activity or preheating temperature to high
Solder Balls – Insufficient preheat or flux-solder mask incompatibility
Insufficient Hole-Fill – Flux activity too low, too low solids, or excessive preheat temperature or too low a contact time with molten solder

•Requirements for a Lead-Free Flux:
◦ Low-activation temperature
◦ Adequate shelf life
◦ High activity level
◦ High reliability
◦ Residues benign or easily remove with water if the paste is a water washable type

•Other Considerations for the Lead-free Flux :
◦ Is the paste for dispensing or printing?
◦ Note manufacturers use different types of activators for different alloys
◦ Select flux carefully to balance activation temperature with thermal profile
◦ What is the compatibility of the flux with the alloy selected?
◦ What are the reliability properties (SIR, electro-migration, corrosion)?

Considerations for Lead-free Solderpaste
•Important properties to consider during selection: ◦Solder Balling Test activity
◦ Wetting Test , specific finishes and solder atmosphere (air or nitrogen)
◦ Voiding Potential, lead-free alloys are more prone to solder voids
◦ Tack Life Over Time
◦ Stencil life and abandon time
◦ Cold Slump
◦ Hot Slump tested to higher temperatures 180-185 C ° .
◦ Shelf-life Testing

Properties to evaluate in-process:
◦Printability
◾Relax/Recovery
◾Print Speed
◾Durability

◦ Component Placement
◾ Drop back for tack

◦ Reflow
◾ Examine solder joint formation on a variety of leads and PWB finishes

• Properties to evaluate after reflow
◦ Thermal Shock
◦ Thermal Cycling
◦ Impact Resistance
◦ Reliability (SIR)

Technical Considerations for Wave Soldering Fluxes Designed for Lead-free Assembly
• Ability to be evenly applicable by spray, wave, or foam applications
• Activator package able to sustain higher preheating temperatures
• Able to be used with a variety of lead-free finishes, bare copper OSP, gold nickel, tin, silver immersion, tin-copper
• Sustained activity, the flux should remain active throughout the contact time with the molten solder, insuring good peel back of the solder
• Low dross potential, the flux must not react excessively with the molten solder as to create large amounts of dross
• The flux must not discolor or char at the higher soldering temperatures associated with lead-free wave soldering
• The flux should not decompose at the higher solder temperatures
• The flux residues must be benign if it is a no-clean flux, and easily washed in hot water if it is a water washable flux type

Technical Considerations for Lead-free Cored Solder Wires
•The flux should not spatter or fume excessively at the slightly higher soldering temperatures associated with lead-free soldering
•The flux should have activator systems designed to solder a variety of lead-free board and component finishes
•The flux must be active enough and remain active enough during tip contact to compensate for the reduced wetting of lead-free alloys
•The flux residues must be benign if it is a no-clean type, or easily removed in hot water if it is a water washable type cored solder
•The residue should not char or darken in color when using slightly higher solder tip temperatures

Source: Kester Solder Co.

How do you prepare a solder pot for lead-free solder?

Tuesday, August 18th, 2015

How do you ready a solder pot for lead-free solder?
It is important to first insure the solder is lead-free solder compatible. High tin alloys tend to leach iron causing dissolution of iron and solder contamination. The dissolution can advance to the point of causing micro-cracks and thinning of the walls, eventually resulting in a solder spill.

Materials that are lead-free solder compatible are:
• Titanium
• Cast iron
• Ceramic coatings
• Melonite coatings
• Specialty coatings, unique to the equipment maker

If a pot is lead-free compatible but contains leaded solder it can be cleaned before lead free solder is added. Cleaning is very important to avoid the introduction of lead. The limit required as per RoHS Directive is only 0.1%. Most lead-free solders will contain a small amount of lead in the range of 0.05%; there is little room for unintentional contamination.

A standard procedure for wave machine cleaning is detailed below:
1.Empty the pot completely
2. Drain any remain solder
3. After cooling use a scraper to gently remove any visible leaded solder
Avoid damage to the metal finish during scrap down
4.Clean ducts, baffles and impeller mechanism thoroughly
5. Clean conveyor chain and fingers with a steel brush, removing all lead-bearing solder particulates.
6. Fill machine with pure tin to clean any remaining leaded solder
7. Run system at 500º F for 2 hours, circulating the solder
8. Empty completely, removing all visible excesses
9. Refill with lead-free solder
10. Do an analysis for lead and iron after running pot for one hour

For dip pots and selective soldering pots, the cleaning is simpler but complete removal
of leaded solder is required and a tin fill is a less demanding process since the volume is
substantially less. A pot analysis for lead and iron is still required.
Note: If a tin wash is not performed it becomes imperative to remove all traces of leaded
solder in all parts of the solder pot area. The risk is highly increased in reference
to lead contamination. Tin washing is therefore preferred
About the author:

Source: Peter Biocca, Senior Market Development Engineer with Kester Inc.

Lead-Free Hand Soldering

Tuesday, August 18th, 2015

Lead-free Hand-soldering – Ending the Nightmares

Most issues during the transition seem to be with Hand-soldering

As companies transition over to lead-free assembly a certain amount of hand-soldering will always be there. An article from Tech Search International last year did say that in Asia where lead-free is highly used, hand-soldering was more of a problem than lead free SMT or wave soldering. Kester has been getting numerous calls in reference to hand-soldering with lead- free in recent months. In fact most problem calls and requests for training through Kester University are related to lead-free hand-soldering and rework. In many cases the assemblers are using materials from various solder suppliers with similar issues occurring in all cases. Often the problems are more than material issues.

Switching to lead-free on Monday morning when Friday operators were soldering with leaded solder is not recommended. Although this seems easily understood some assemblers have attempted this, with line stoppages occurring only a few hours into lead-free hand-soldering. Operator complaints, loss of reliability and poor joint quality were experienced. This could be a production engineer’s nightmare but it need not be this way if the basic concepts of hand-soldering are revisited, some experience gained prior to the transition and adequate training of operators is performed before and after the switchover.

Here are some questions often asked by assemblers in reference to hand-soldering with lead-free solders. These are in fact also some of the issues addressed during the lead free hand-soldering on-site audit done through Kester University.

Which alloys and fluxes are compatible with lead-free hand-soldering?
The limiting factor with lead-free solders is probably its availability in wire form; some alloys are not easily drawn into wire, as is the case with tin-bismuth solders. At this time the most popular alloys used to make wire are tin-silver-copper and tin copper based solders. This compliments the industry well at this time where 68% of SMT assemblers and 50% of wave assemblers have chosen tin-silver-copper (SAC) solders. In wave soldering 20% have chosen tin-copper (SnCu) based solders due to the cost of lead-free solder bar. Wire solders for hand-assembly are therefore readily available in these two alloys.

The main differences between SAC and SnCu solders are the melting points; the melting temperatures are approximately 217ºC and 227ºC respectively. From a soldering performance perspective, SAC wets more readily than SnCu based solders, so flow with SAC solders, everything else being equivalent, will be better. Both SAC and SnCu solders are available in no-clean, water washable and rosin based flux formulas. No-clean accounts for over 85% of the total wire usage while water washable is less than 15% and rosin based fewer than 5%. These numbers apply to
North America. In other parts of the world no-clean is dominant.

What are the key variables in choosing a good lead-free solder wire?
By far the flux content in the wire will be a critical factor in determining wetting behavior.
Lead-free solders such as SAC, SnCu and the higher temperature option tin-antimony SnSb wet a little slower than 63/37 when compared using similar conditions in wetting balance tests.

Lead-free solder wires should contain at least 2% flux by weight. Leaded solders are available with lower flux percentages as low as 1% wt/wt; this low flux volume will not work well with lead-free.
Typical flux distribution in a solder wire, the density of the flux is close to 1 g/cc; therefore the volume is
more obvious in the cross-section. Multiple cores are used at times but the percent is usually 2 or 3 %
for lead-free. Less flux results in more difficulties during soldering.

If wetting is still too sluggish 3% flux in the wire may be tried but this will give higher residues, not always cosmetically appealing in no-clean applications. The addition of flux using a squeeze bottle is normally not acceptable due to over application issues. This is not acceptable for no-clean applications. Another important point is to insure the flux is designed for lead-free applications and therefore it should be able to withstand higher soldering tip temperatures without charring, spattering and decomposition. Some fluxes may smoke more when using hotter tip temperatures.

When choosing a solder wire make sure to observe the flux IPC classification. Many no-cleans meet the ROL0 classification meaning they are rosin based, low activity and halide free. These are the most reliable and meet the SIR and corrosiveness tests in the IPC specification. With lead-free there is a tendency to use higher activity to compensate for the reduced wetting; this is not always a good idea. Water washable fluxes will be more active classed often as ORH1 and do better with lead-free soldering. However insure the residues are still completely removable in hot water; doing ionic contamination testing is recommended. If ionic contaminants still
remain after water washing, a clean process change may be warranted such as increasing the cycle time, water temperature or a change of the cleaning agent. In comparative studies done with SAC and SnCu wetting balance tests indicate that using the same flux types that SAC out-performs SnCu solders in the time required to reach maximum wetting. This applies also to SnCu solders with dopants of nickel, cobalt or other additives. In choosing an alloy it is important to determine the overall solderability of the parts to be assembled. If the parts are older, more oxidized, manually handled SAC solder may be a better choice.

What are the main changes associated with lead-free hand assembly cosmetics?
Lead-free solders flow a little slower than 63/37 using the same activation levels for the fluxes. The contact angles are slightly larger and feathering out of the solder is therefore less pronounced. The solder joints tend to be less reflective than 63/37 solder. Some retraining is required prior to a full transition to lead-free is done. In some cases certain shrinkage effects as described in Section 5 of the IPC-STD-610D occur. The IPC-610 classifies these as soldering anomalies and not necessarily defects. As mentioned on page 5-22 of the above document, it is not a defect for Class 1, 2 and 3 if the tear bottom is visible and the shrink hole does not contact the lead, land or barrel wall. See the photos below for examples taken from the Kester laboratory.

What is the best soldering tip temperature for lead-free SAC and SnCu?
The temperature of the tip or contact temperature is very important to ease the lead-free hand-soldering operation. When using 63/37 solders temperatures as low as 650ºF have been used but with lead-free 700-800ºF is best. The higher temperature does compensate for the slower wetting exhibited with these lead-free alloys. Above 800ºF issues of board and component damage may arise; at lower temperatures cold solder joints and flagging are the normal complaints. Higher temperatures and longer contacts with the parts to be soldered may also increase the intermetallic bond layer. So avoiding prolonged contact and repeated rework is not recommended. The above diagram shows what happens as the bond layer increases in thickness a higher risk of embrittlement occurs. The risk of de-wetting also increases with higher temperatures.

How about the soldering tips with lead-free solders?
Lead-free tips are required however just as important is the choice of tip design. Lead free is less forgiving and the right tip for the job will go a long way in prevent defects. Chose a tip with enough heat delivering capacity. Fine point tips cannot be used in all applications and in some cases a tip such as a chisel type is best suited to deliver sufficient heat to the parts to be soldered.

How about tip life with lead-free solders?
Tip life will be reduced with lead-free solders and it is important to choose tips really
designed for lead-free soldering. Many tips are only tinned with lead-free solder and the iron plating is no different than traditional soldering tips. High tin solders like to dissolve iron and this reduces tip life. Some assemblers have reported important reductions in tip-life for example a manufacturer reported that with 63/37 the tips lasted 3 months with lead-free the tip-life was only 3 weeks. Not all soldering tips are equal when comparing dissolution rates so choosing tips carefully and asking for more compatibility information is a good practice. Lead-free tip failure after 3 weeks Cross-section of typical solder tip, with lead-free the solder is lead-free

How can a good lead-free hand-soldering process be had, which will ease the lead-free soldering operation?
In a recent study, which appeared in the Lead-free Update by Tech Search International in December 2004, hand-soldering was found to be more problematic to implement when compared to lead-free wave soldering and SMT.
The reason could be that hand-soldering is more operator dependant than reflow and wave soldering but also the surface tension in lead-free solders is slightly higher.

Wetting or spread is also a little slower when compared to 63/37.
To reduce operator issues and reduced wetting proper optimization of the soldering process is key. To avoid issues use a flux content of 2-3% by weight in the solder wire, use a solder tip temperature of 700-800º F. Also Tin-Silver-Copper (SAC) solder will flow more readily than Tin-Copper (SnCu) solder.

The main issues encountered with lead-free hand-soldering are cold solder joints, poor wetting, flagging and de-wetting. These can be avoided.

A step-by step process transition would be as follows:
Insure the tips are designed for lead-free
Insure the temperature is set to 700-800 ºF
Insure the flux content in the wire is a least 2% wt/wt
Use LF tips with the longest life
Use the correct tip for the job
Insure the parts are easily solderable with the chosen flux
Avoid prolonged contact times
Avoid needless reworking of the joint
Avoid the use of additional liquid flux
Which defects or issues can appear and how can they be avoided?
The common issues reported with lead-free are:
Grainy joints
Cold solder joints
De-wetting
Flagging
Poor wetting and wicking
Flux charring and darkened residues
Difficulty with the cleaning of residues
Grainy joints can be due to too high a tip temperature and the dissolution of the metals
to be joined.

Cold solder joints can be due to several things such as too low a tip temperature, too weak a flux or insufficient flux in the wire. De-wetting can be caused by prolonged tip contact and the dissolution of the plated
metals, exposing a less solderable surface. Too high temperatures can also cause this. Flagging can be caused with the use of too high soldering tip temperatures or the use of solder wires with low volumes of flux. Flux activity may be low also and prolonged contact with the iron is de-activating it.

Flux charring with no-cleans and cleaning difficulties especially where water washable is used can be due to soldering temperatures being to high or the flux is not properly designed for the higher temperatures required for lead-free. Avoiding prolonged contact and using lower soldering temperatures can help with this situation.
My soldering iron tips are charring, turning black and de-wetting when I use lead free solder wire, what can I do?

Not all fluxes are created equal and some are thermally incapable of sustaining the higher soldering temperatures used with lead-free solder. A recent video clip from OK International demonstrates this well when two solder wires are compared side by side and this is called the “black tip syndrome”. Less thermally stable resins turn the tip black and makes re-tinning more difficult also. Once “black tip syndrome” occurs the reduction in heat transfer makes lead-free hand soldering difficult, tip life is reduced, tip costs and operator frustration goes up and
reliability goes down.

Proper flux selection, using lead-free tips and lead-free hand solder process training for
operators will offset these costs.

The important points to help avoid these problems are listed below.
Use lead-free solder wires with lead-free designed fluxes
Avoid using too high temperatures
If tip tinner is used, wipe excess tinning material on a clean sponge
Do not use pressure to compensate for lack of wetting
Use the right tip geometry
Use the correct wire diameters
Segregate work areas for lead-free and leaded
Identify lead-free irons and work stations
Train all operators on the expectations

These are some of the questions asked by customers moving forward with lead-free assembly. A little training goes a long way in avoiding costly issues with the hand soldering process.
Although the process is more operator dependent using the tech tips mentioned above can make hand-soldering less frustrating for the operators and engineers. Maintaining the same levels of reliability they are accustomed to with leaded soldering is therefore very achievable with no nightmares of poor joints or reduced production output. .

Source: Peter Biocca is Senior Market Development Engineer with the Kester Co. He is a chemist with 24 years experience in soldering technologies.