Bob: Please help us understand the effect of changing to lead-free solder paste on our processes better. Compare the following for tin-lead and lead-free solders: * Size of stencil apertures � amount of solder necessary for a reliable solder connection. * Reflow profile and the effect of this on boards and components.
Many lead-free solder formulations are proprietary. What are thoughts on near to long term procurement issues surrounding proprietary lead-free solder formulations?
On all the trials I have done I have made no changes to the stencil thickness or apertures than the normal changes we make for our process. I have not changed any thing in terms on volume of solder for more reliable joints. I fact I have not read any thing to suggest this is necessary. You do seem to get more bulbus joints with wave soldering with tin/silver and tin/copper probally due to the poor drainage.
The basic profile is changed to achieve reflow by changing the last few zones. Boards dotend to sag a little more, more on wave than reflow. That is one of the reasons I like to see people reconsider the use of centre board supports rather than expensive pallets which I am not a fan.
Some General Observations on lead free
Although liquidus temperatures are higher, peak reflow temperatures are not significantly higher than with conventional Sn-Pb Eutectic alloy.