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March 2007

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Subject:
From:
Paul Reid <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paul Reid <[log in to unmask]>
Date:
Thu, 1 Mar 2007 15:46:20 -0500
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Hi Dave,

I agree with you.  I do not see any thing obvious in the microsection posted that would indicate the material was degraded by your thermal cycling. 


Three years ago we suggested a cyclic thermal mechanical analysis (TMA) protocol considered by the IPC to test dielectric materials. There are two parts to this protocol.  The first part determines glass transition temperature (Tg) and coefficient of thermal expansion (CTE).  The second part is a cyclic assembly and rework cycle 6X to 260°C follow by a time to delamination at 260°C (cT260). In LA last month there was some discussion on this method.  I have been asked to resubmit the method for review.

You might find this protocol useful in comparing candidate materials.  We use this protocol in conjunction with reliability testing.  Armed with reliability testing and cT260 we appear to have a very powerful tool to evaluate materials.  We have been please with this protocol's ability to discern material related reliability problems.

I will try to contact Steve Gregory and see if he would be willing to post this method on his wed site.

In the mean time I will send you a copy.


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
[log in to unmask] <mailto:[log in to unmask]> 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dave Seymour
Sent: Thursday, March 01, 2007 2:26 PM
To: [log in to unmask]
Subject: [TN] Laminate Qualification.


Back in the fall '06 I emailed the forum about how to
qualify pcb laminates for the higher temperature required
by Lead Free assembly.

One of the suggestions out of the many responses was
"a cyclic T260 (cT260) protocol where a material is thermal
cycled to 260 6 times, to simulate assembly "

The Manf. Engineer went out and had our CM run a 14 layer  FR-408 material
pcb with via filler through this profile 6 times:

http://stevezeva.homestead.com/files/Lead_Free_Profile_V_Sample.pdf


The cross section came back looking like these:
http://stevezeva.homestead.com/files/cross_section_1_via_fill.jpg

http://stevezeva.homestead.com/files/cross_section_2_via_fill.jpg


I need some help and opinions on what I am looking at.

The first thing I noticed was that the reflow profile never gets the
temperature higher than 249C in one location. And the time above this
temperature seems short to me. With most of the time above only 217C.
Lower than I would think is need for Lead Free reflow.


Second, The cross sections look fine to me. I don't see anything 
coming apart or bulging. I'm I missing something?

I'm looking to go back to the Manf. Engineer and comment on this
test. I'm think that this is a nice test of low temperature reflow. 


Thanks to Steve and his wonderful web page of knowledge.

Thanks to all in advance.

Dave Seymour


-- 
Dave Seymour, CID+
Catapult Communications Inc.
800 Perimeter Park Dr, Suite A
Morrisville, NC 27560

Direct: (919)653-4249
Main: (919)653-4180
Fax: (919)653-4297

[log in to unmask]







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