I disagree with the general consensus that higher Tg is better.

The best response is ... it depends.

Generally high Tg materials are more reliable than low Tg materials but not in every application. Also there are high Tg materials on the market that offer NO reliability advantage over low Tg materials. Some high Tg materials lose all advantage over the lowest Tg material in sequential lamination applications.

I know what I am saying is counter intuitive but that is what we have demonstrated repeatedly, doing reliability testing of representative coupons, over the last seven years. 

There are lead-free applications where low Tg material withstands lead-free assembly temperatures mainly due some DICY cured materials have a high Td than phenolic.

If you have a hi-rel application then high Tg is recommended. With some lower end applications (low layer count, low aspect ratio) DICY cured is just as robust as the more expensive phenolic cured material.

I suggest testing the current material and two "high performance" materials. Rank the materials by testing reliability on coupons with your design and construction, preconditioned to your actual assembly temperatures. You may not need to change materials at all. You may need to limit assembly to 245°C.

Do not forget that material delamination de-stresses test coupons giving false positive thermal cycles to failure. You must test both the reliability of the copper and material to evaluate robustness in lead-free applications.

Sincerely,

Paul Reid

Program Coordinator

PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1

613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lenny Carter
Sent: Thursday, August 14, 2008 12:20 PM
To: [log in to unmask]
Subject: [TN] TG 130 or Tg 170 for ENIG

Hey technetters- We adopted the ENIG finish for our RoHS compliant parts 2 years ago.  We recently had discussions with our primary pcb vendor and they recommended we switch to a Tg170 FR4 material for our pcbs instead of our standard Tg130 we have been using for years.
This recommendation was made because of the higher reflow temperatures necessary for the lead free process.
 
Is this standard practice?  we are a little hesitant to make the switch as it would mean an approximate 5%price increase on all our pcbs.
 
Any input is appreciated.
 
thanks, Lenny Carter  ERG, Inc.   www.ergpower.com
 

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