What happened to the 1:1 ratio of the top to bottom Cu pads.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, March 02, 2010 7:13 AM
To: [log in to unmask]
Subject: Re: [TN] BTC rework, Square SJs
Hi gang! A picture is worth a 1000 words (thanks Steve)! Sure enough, that
would be a square solder joint but its root cause is that too much solder
paste is being used. The final reflowed solder joint has squeezed out onto
the soldermask surfaces thus creating a square appearance. This shape may
also be the results of the solder surface tension not being able to
support the component package weight. Chris - is there any issue with
potential shorting due to the shape? Very interesting.
Dave Hillman
Rockwell Collins
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Steve Gregory <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
03/01/2010 09:33 PM
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TechNet E-Mail Forum <[log in to unmask]>; Please respond to
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Subject
Re: [TN] BTC rework, Square SJs
Hi Chris,
Your pic is up!
http://stevezeva.homestead.com/files/29903_sn_79_perimeter_a.jpg
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Monday, March 01, 2010 9:27 PM
To: [log in to unmask]
Subject: Re: [TN] BTC rework, Square SJs
Thanks Werner. Gotcha. BTCs will keep us in business for awhile.
My biggest concern on this job is that the customer is going to ask
"what's
up with the funny shaped joints?".
It sounds like Bev has the T-shirt already.
I sent a picture to Steve.
Chris
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Monday, March 01, 2010 1:56 PM
To: Chris Mahanna; [log in to unmask]
Subject: Re: [TN] BTC rework, Square SJs
Hi Chris,
The problem with this SJ is the low solder joint height 9=reduced
reliability) and the stress concentration geometry from SMD.
Werner
-----Original Message-----
From: Chris Mahanna <[log in to unmask]>
To: Werner Engelmaier <[log in to unmask]>; [log in to unmask]
<[log in to unmask]>
Sent: Mon, Mar 1, 2010 1:08 pm
Subject: RE: [TN] BTC rework, Square SJs
In cross section, the vertical sides of the joint are straight. I assume
it
has more/less retained the shape of the [trapezoidal?] stencil.
Chris
From: Werner Engelmaier
[mailto:[log in to unmask]<mailto:[log in to unmask]>]
Sent: Monday, March 01, 2010 12:52 PM
To: [log in to unmask]<mailto:[log in to unmask]>; Chris Mahanna
Subject: Re: [TN] BTC rework, Square SJs
Chris,
What do you mean by "square joints?"
Werner
-----Original Message-----
From: Chris Mahanna <[log in to unmask]<mailto:[log in to unmask]>>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Mon, Mar 1, 2010 12:15 pm
Subject: [TN] BTC rework, Square SJs
Are square joints simply due to the small mass of the components, or is it
possibly an indicator of insufficient heat? We have no indication that
any
of
the paste didn't flow. Wetting looks good. All evidence is from
microsection.
Thanks,
Chris
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