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August 2008

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Subject:
From:
Bob Willis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bob Willis <[log in to unmask]>
Date:
Fri, 15 Aug 2008 07:29:40 +0100
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Have to also agree with Paul.

My main experience is with standard 1.6 and 2.8 of both normal, what ever
that means, and different high Tg and height Td materials for 8 layer
boards.

Problems seen on the higher end materials are:

Epoxy cracking at pad interfaces
Poor copper adhesion on through holes
Poor foil adhesion
Very inconsistent joint shear forces due to pad adhesion


Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
Tel: (44) 1245 351502
Fax: (44) 1245 496123
Mobile: 07860 775858
 
www.ASKbobwillis.com
 
New Bob Willis "Printed Board Inspection & Quality Control Workshop" 3rd
September www.ASKbobwillis.com/PCBworkshop.pdf 
 
Book your place on Bob's "Step by Step Failure Analysis Workshop" 11th
September  www.ASKbobwillis.com/faworkshops.pdf
 
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: 14 August 2008 20:27
To: [log in to unmask]
Subject: Re: [TN] TG 130 or Tg 170 for ENIG

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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