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August 2006

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Subject:
From:
"Whittaker, Dewey (EHCOE)" <[log in to unmask]>
Reply To:
(Leadfree Electronics Assembly Forum)
Date:
Fri, 25 Aug 2006 07:40:49 -0700
Content-Type:
text/plain
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text/plain (346 lines)
Thank you, Lee. I got it and I will let you know what we find out.
Dewey

-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Lee Parker
Sent: Friday, August 25, 2006 7:08 AM
To: [log in to unmask]
Subject: Re: [LF] Copper Pad Peel Strength

Dewey



http://pcdandm.com/cms/cms/content/view/2802/95/



Best regards



Lee



J. L. Parker Ph.D.

JLP Consultants LLC

(804) 779 3389





-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey
(EHCOE)
Sent: Friday, August 25, 2006 9:58 AM
To: [log in to unmask]
Subject: Re: [LF] Copper Pad Peel Strength



Lee,

Good work. Could I get a copy of that or a link. We are starting to see

some of this and I have few theories on some new variables that been

thrown into the fray and would like to establish a good baseline test.

Dewey



-----Original Message-----

From: Leadfree [mailto:[log in to unmask]] On Behalf Of Lee parker

Sent: Friday, August 25, 2006 6:24 AM

To: [log in to unmask]

Subject: Re: [LF] Copper Pad Peel Strength



Amol



I published a paper on this issue in this months PC Design and

Fabrication.



In the paper, I go through a rigorous mathematical analysis of the peel

strength measurement. Essentially, I found it does not measure the bond

strength of the cooper, but rather a vector combination of shear and

tensile

stresses. For thermal failures the desired measurement is the shear

strength

of the bond. The plane and magnitude of the vector is highly dependent

upon

the radius of curvature and thickness of the copper being peeled from

the

substrate as well as the peel angle. In fact the dependence of the peel

strength is exponential dependent upon all three variables. So by very

minor

adjustments you can rotate the stress vector direction and magnitude and

get

a significant modification in the result (peel strength). We have all

known

this to be the case for years, I have only quantified the analysis. Keep

in

mind the ultimate tensile strength and the ultimate shear strength vary

by

an order of magnitude. So minor changes in the variables mentioned above

produce significant changes in the peel strength.



What I proposed in the article is the use of a double lap joint that is

pulled to failure. The test vehicle I proposed creates only a shear

stress.

This should be a huge improvement over the peel strength measurement.





----- Original Message -----

From: "Kane, Amol (349)" <[log in to unmask]>

To: <[log in to unmask]>

Sent: Friday, August 25, 2006 7:29 AM

Subject: [LF] Copper Pad Peel Strength





Dear Technetters,

We are having instances where copper pads (Under BGAs) are being lifted

off

ENIG Boards almost too easily during rework. We use the same thermal

profile

on each board (for the same component removal) and only some show this

phenomenon. Is there a test or standard to test the copper adhesion @

incoming to see whether it's the fab (i.e. are the boards coming to us

with

poor copper adhesion strength to being with) or the process that's doing

this. The board is heated upto 120 C when the component is reflowed for

removal. Also, is there data to show the decrease in Cu adhesion

strength

with temp?



Thanks,



Amol Kane

M.S (Industrial Eng.)

Process Engineer

Harvard Custom Manufacturing, Inc.

941 Route 38  Owego, NY 13827

Phone: (607) 687-7669 x349

[log in to unmask]

www.harvardgrp.com









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