Assembly acceptability Lead-free soldering

As many PCB fabricators and assemblers transition to lead-free processing, they are faced with solder alloys that have an operating temperature up to 30°C (54°F) hotter than the traditional eutectic tin-lead solders. These increased soldering temperatures raise concerns about the ability of the solder mask (as well as all other materials) to resist embrittlement, discoloration, loss of adhesion, and cracking with repeated exposures to the higher temperatures. Some existing products may not be acceptable for lead-free processing. 

The PCB needs to be supplied at a quaUty level that is capable of withstanding the assembly process, as it will undergo several operations to mount and rework components and connectors. This assembly and rework process has gotten more complicated and damaging to the PCB, especially with the introduction of lead-free products. The acceptability criteria should attempt to anticipate the conditions of the soldering process to ensure the PCB wiU survive the assembly and rework process and stiU function as intended. 

Understanding the stresses to which the assembly process exposes the PCB is fundamental in defining the acceptability criteria. Process elements such as leaded or lead-free, reflow or wave solder, double-sided reflow, hand-soldering, and rework all significantly impact the requirements of the PCB. 

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