If I could only find someone who knows how to make Princess Phones...

-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Lester Subrattee
Sent: Friday, April 21, 2006 4:13 PM
To: [log in to unmask]
Subject: Re: [LF] Aging Performance


Werner, do you know any good consultants ?

Smile..

LS


 -----Original Message-----
From:   Werner Engelmaier [mailto:[log in to unmask]]
Sent:   Monday, April 17, 2006 11:36 AM
To:     [log in to unmask]
Subject:        Re: Aging Performance

Hi 'mtaylor,'
> 1)   I posted a peripheral question about determining if a peak
temperatur=
e=20
> could
> be detected by looking at the microstructure of solder joints.
> A: No, you cannot tell from the solder microstructure what the peak=20
temperature reach was. The solder micro structure depends solely on the
rate=
 of=20
cooling--fine grain structure=3Dfast cooling; coarse grain
structure=3Dslowe=
r cooling. No=20
practical advantage is to be gained from cooling products faster to get
fine=
r=20
grain structures--however, you may get fractured SJs because of thermal
shoc=
k=20
loading. Fine grain structures result in more cycles during accelerated=20
testing, however, SJ grain structure is inherently unstable, and thus the
ap=
parent=20
gain in reliability is an illusion.

> 2)=A0 Can you look at a board that has failed in a lead-free process and
s=
ee
> if the board saw the same thermal experience as other boards in the lot?=
=A0 By
> thermal analysis?=A0 By metallurgical examination?
> A: No, you cannot. However, you can tell whether or not it sustained the
s=
ame=20
level of damage. You get similar levels of damage by multiple exposures
to=20
lower T-levels or one exposure to a high T-level. Moisture content will
also=
=20
play an important role as does resin content and the degree of cure of the
r=
esin.

> 3)=A0 Within a board, could you look at a BGA for example, near a
failure,=
=20
> and
> see if it saw more thermal experience (rework) than the surrounding board?
> A: Yes, but that determination is destructive, because you have to
section=
=20
the PCB.

> Do you know if an acceptable procedure has been published that we could=20
> reference in support of an analysis? The answers help direct where to go
t=
o
> find a solution to prevent a future failure.
> A: No, there is no established procedure to my knowledge. I can tell
you=20
where to go to prevent future occurrences--engage a consultant, if you do
no=
t have=20
the in-house expertise.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com


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