Tin Lead Assembly
So you have decided to stay with Tin Lead for your electronic modules.
You have an exemption or you will never be asked to supply a module that could end up subjected to RoHS compliance. No need to worry – right? Wrong!
With so many component suppliers switching to Lead Free what will your BOM look like by July 1st 2006? How about the next year and the year after?
By now you should have completed the following items
- All vendors have been contacted to verify continuity of existing components and bare boards.
- Where suppliers are switching to lead free, alternate suppliers have been sourced.
- Approval has been obtained from customers to accept alternate suppliers.
- Critical assemblies have been built with alternate supplier components and reliability tests have been completed with no failures.
- Re-tinning facilities have been contacted, audited and approved.
- Equipment or process put in place to verify solderability of aged tin lead or re-tinned components. This will become more critical as time increases and the sources of tin lead components dries up.
Some problems when using Tin Lead to solder Lead free components:
Failure of BGA modules: BGAs with high temp SAC alloy balls when soldered with Tin Lead can suffer a variety of problems from voiding to cracks in the joint.
Components with Bismuth (Bi): Lead free components from Asia may have a high level of Bismuth which when used with SnPb can form a tertiary eutectic of Sn Pb Bi that has a Liquidus of 96°C.
Components plated with Ni Pd Au can be difficult to solder at 212°C.
Components plated with 100%Tin will not reflow at the lower temperatures used with Sn Pb. Plated tin has a greater propensity to grow whiskers than reflowed tin. Modules may suffer more failures from tin whisker growth than Lead Free.
Retinning of devices may leave you with an unknown intermetallic layer and may compromise the integrity of the package to lead interface.
Solderability Testing and Solutions, Inc is here to help with any problems you may be experiencing. We can supply solderability test equipment or testing services for your old Tin Lead or re-tinned components.