Hi Dennis, IPC LF Listservers,

Back again after reading GGrossman and WernerE's note.

>I'm wondering if there is a general consensus when it comes to selecting a
>laminate material for PCBs for Lead Free. Is the standard FR4 Tg 130C
>adequate for Lead Free or would we need to move towards a higher grade
>>Tg170.

NO general consensus. Certain products can be built on FR4 and other
laminates depending on the assembly soldering stresses involved, and the
life expected.

It all depends on your laminate, your components, your soldering material,
process, men/omen, management.

Read GGrossman's note.

>I'm a little confused in that some say it is required to move to the higher
>Tg to accomodate for the higher Assembly temperature while others say Tg
>170C is unnecessary. Are people moving towards to the higher Tg as an
>assurance or is it a requirement for the higher processing temperature?

Hopefully from WernerE's note about creating an equation you get some idea
of what is going on in terms of mismatched thermal expansion and set in
stress once the solder joint solidifies and comes back to room and then
operating temperatures. And from here the little puppy goes out to live
it's life of electronic connectivity.

Mostly I believe that most are moving to higher Tg because of many reasons.
Tg is one of those catch all technology phrases that people have heard and
don't really know so "higher Tg" sounds like I/they are doing a better job.
After all isn't higher soldering temperatures and higher Tg language and
idea connected.


The bottom line is that you have to know your product in many ways that is
from the materials, to the manufacturing (assembly), usage and expected
life expectancy.

Yours in Engineering, Dave
Y i Engr, MA/NY DDave

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