The Restriction of Hazardous Substances directive is more commonly know in the electronics industry as RoHS. The RoHS directive is aimed at restricting the use of 6 hazardous materials in the manufacture of electrical and electronic devices as follows:
• Lead (Pb)
• Mercury (Hg)
• Cadmium (Cd)
• Hexavalent Chromium (Hex-Cr)
• Polybrominated Diphenyl Ether (PBDE)
• Polybrominated Biphenyls (PBB)
RoHS 1 is closely linked with the Waste Electrical and Electronic Equipment Directive (WEEE // 2002/96/EC) which sets guidelines for the recovery, collection and the recycling of electrical goods to solve the problems associated with tremendous amounts of toxic waste.
The effect of these two initiatives have had on the electronics industry varies greatly depending on the target sales market and the end use of the product. The overall supply chain from individual components to bare printed circuit board manufacturing has shifted from a predominantly tin-lead alloy based market to one that caters almost exclusively to lead-free finishes. The result has been limited supply, and in some cases, complete elimination of tin-lead plated components. This has, in effect, forced manufacturers to make design and process changes on products that were traditionally tin-lead based.
The primary difference between lead-free and tin-lead solders, from a desoldering, repair and rework standpoint, is the temperatures required to form a proper inter-metallic bond. For the most widely used tin-lead alloys such as Sn60 Pb40 or more commonly Sn63 Pb37 (eutectic), the melting point is 361° (183°). The most commonly used lead-free alloy, Sn96.5 Ag3.0 Cu0.5, commonly referred to as SAC 305, has a melting point of 422° F (217° C) to 428° F (220°). The resultant increase in melting point will have the effect of reducing the overall process window and can change the traditionally accepted appearance of the finished product.
Prior to the implementation of the RoHS and WEEE directives, the use of tin-lead solder was widely accepted and it’s reliability was exhaustively tested and it’s appearance easy to inspect. Virtually all electronics assembly were designed to withstand manufacturing with the commonly known tin-lead solder and the temperatures that they require. Further, virtually all specifications written for the compliance of electronic assemblies in the military, government and consumer markets were written with the same tin-lead alloy in mind.
Today the use of lead-free solder alloys that comply with the RoHS and WEEE directives are in wide use and while segments of the electronics industry continue to perform reliability and life-cycle testing on complete RoHS and WEEE compliant assemblies and manufacturing processes, the use of individual lead-free components and board finishes is commonplace.
The Process Guides contained herein will reference the common tin-lead (Sn63 Pb37) and lead-free SAC 305 (Sn96.5 Ag3.0 Cu 0.5) alloys.