Good morning Kitty;
It isn't so much the Glass Transition temperature (Tg) you need to worry
about so much as the total summation of the Z-axis expansion both above
and below the stated Tg for the processing temperature. Unless chosen
carefully a high Tg board can give you a bigger expansion over the
applied (process) temperature.
As an aside the board design can make matters worse, for example if the
aspect ratio of any vias is greater than 6:1 (target 4:1) the likelihood
of barrel cracking becomes even more significant with LF.
Just to give you something else to worry over, modern laminates tend to
absorb moisture very readily and if uncontrolled the extra thermal
stress during LF processing can cause delamination. Is the environment
where the boards are processed controlled?
Hope this helps.
Regards
Bob Gregory
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Kitty Hines
Sent: 07 November 2012 23:30
To: [log in to unmask]
Subject: [DC] PCB Material for Lead-Free RoHS
Hello,
I hope all is well with everyone. I'd like to get advice from the
experts! And I know where to find them...
I have a question regarding Board Material for Lead-free, RoHS design.
I
am dealing with high-volume/low-cost processes, usually sent overseas
for
bare board manufacturing. Another issue is, we are using a lead-free
FR4
type, HASL finish.
1) When specifying board material, is it necessary to specify a higher
temperature rating?
2) What are the advantages? Disadvantages, other than cost?
Thank You In Advance for your help,
Kitty
Kitty Hines
The Chamberlain Group, Inc.
(630)516-6655
[log in to unmask]
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