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Lead Free Substrate

John S


Lead Free Substrate | 2 February, 2005

Some of the research on Lead Free I've done indicates that a pcb with a higher Tg (>170C) would be required for a lead free process. Can anyone comment on whether that is necessary or just conservative? Thanks John S

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Lead Free Substrate | 2 February, 2005

I would call it conservative, but definitely recommended. It sort of depends on your assembly design. We have run 140 boards lead free but are now using the 170.


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Lead Free Substrate | 2 February, 2005

Higher Tg values are only one thing to look out for. Two other things that are very important to watch are the Td or Decomposition Temperature (the temperature that the epoxy actualy starts to break down), and the CTE for the material. Some Tg 140 materials actually will perform better than Tg 170 materials in a lead free process because they have a higher Td value. I have seen Tg 140 boards make it through 4-6 Pb-free reflows without issue, but have also seen Tg 170 boards come out looking slightly charred (like a piece of toast).

Also, watch the CTE values. If the material has a higher CTE, then you could be looking at potential via reliability problems.

Like everything dealing with lead-free, there is no one magic solution for laminates. If some one tells you that they have the perfect material, beware, do your homework.....

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Lead Free Substrate | 24 February, 2005

Here is an interesting article that supports T2s comments about Td:

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John M


Lead Free Substrate | 7 March, 2005

It has been my experience that the standard Fr4 material (Tg 135c) will discolor when processed at the new higher temperatures required for the high tin alloys... We have been using the High Tg Fr4 (Tg 170c) for many years to ensure this does not happen....

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