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December 2002

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From:
sunnyliu <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 4 Dec 2002 10:01:34 +0800
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  I agree with Russ. You can read the IPC standard 486 or 579, also There is a via reliability paper in the recently PC FAB.

----- Original Message -----
From: "Russ Steiner" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, December 03, 2002 8:53 PM
Subject: Re: [TN] via cracking


I can't point you to any white papers, but it via cracking is always related to thermal expansion.   If there were no Z-axis expansion, the barrel would not crack.  It's my experience that there are 3 typical causes:

1.  Insufficient plating in barrel.  (Where too thin and any thermal stretch fractures the plating).  Smaller vias tend to exhibit (high-aspect ratio Z-ax vs dia)
2.  Excess Z-axis expansion. (Compliments of delamination in ML bds or excessive thermal shock)
3.  Poor hole quality (Resin smear in hole, debris / fibres / chemicals left in in hole, etc prior to electroless or other first plate)

Doing a cross section is a great way to see if you have plating or delamination at the cracked barrel location.  That's almost always shown clear definition of the fatigue and failure and led me to the root cause.

Russ


-----Original Message-----
From: TechNet E-Mail Forum.
Sent: 12/2/2002 11:30 PM
To: [log in to unmask]
Subject: Re: [TN] via cracking


> ----------
> From:         Dennis Bang[SMTP:[log in to unmask]]
> Sent:         Monday, December 02, 2002 11:30:18 PM
> To:   [log in to unmask]
> Subject:      Re: [TN] via cracking
> Auto forwarded by a Rule
>
I did not give any details as I wanted to understand all the possibility
which could contribute to via cracking. Does anyone have white papers on the
subject?

Assuming the boards were made correctly, what in the manufacturing process
could contribute to this defect. From the report it is mainly occuring near
ICs (QFPS, SOICs).


-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Tuesday, December 03, 2002 2:42 PM
To: [log in to unmask]
Subject: Re: [TN] via cracking


Hi Dennis,
Via barrel cracking typically--you do not give any details--occurs as the
result of the much larger thermal expansion of the resin surrounding the via
than the copper of the barrel during soldering processes. There are
contributing factors, i.e. PWB design, hole quality, barrel copper quality,
resin content, etc.
I give a one-day workshop on this [see outline at website].

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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