Hello all,

Few questions, while updating my PCB quality requirements document:

1.                  Is it enough to specify "matte immersion tin" or
"immersion silver" as the finish definition? Are there any detailed
characteristics of deposited materials type, thickness, or quality to
list? Are there any reference standards?

 

2.                  Regarding the Td issue: Following a thread that was
discussed here few months ago, I specified high Td value for my
lead-free PCBs (330 degC minimum). I read the interesting answer of
Sherif Refaat to Werner Engelmaier's question. However, in IPC/JEDEC
conference in Frankfurt some presenters claimed that all the lead-free
qualification tests they did were on low Tg (hence their Td is typically
~ 300 degC) FR4 boards. I assume that the vast majority, if not all, of
the experiments were done on thin boards with low layers count. Hence,
the set temperature of the oven was not much higher than the pads
temperatures, and by far lower than the Td value of the materials. Can
anyone estimate the effect of shrinking the difference between the PCB
surface temperature to its Td value? Is there any quantitative guideline
regarding the rate of loss of volume of the resin? Is there any
knowledge - theoretical or empirical - on the relationship between loss
of resin volume and the PCB reliability?

 

Regards

Ofer Cohen

Manager - Quality, Reliability and Production Technologies

Seabridge - a Siemens company

 

 


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