Hi Bev,
We did a horizontal section from the component side.
At least for this one particular sample there is a correlation between the columnar (square) joints and relatively less paste. Thanks for the clue.
Dave, the bulbous joints appear to have too much paste, but not so much to short. The columnar joints appear to stretch or maybe even retain the shape of the stencil. I'm sure that the small board side lands, soldermask and surface tension play a role. Unfortunately I've got to move on to the next project--inspecting hundreds of dip-and-look.
Chris
-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: Monday, March 01, 2010 1:17 PM
To: TechNet E-Mail Forum; Chris Mahanna
Subject: RE: [TN] BTC rework, Square SJs
Chris,
I think you will find that this happens when a particular joint does not
have enough solder paste printed with respect to the rest of the joints.
There is enough solder so there is not an open or a head on pillow
(HoP), but not enough to give what we normally expect (slightly
bulbous). The joint gets "stretched" and you end up with more or less
straight sides.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Monday, March 01, 2010 1:08 PM
To: [log in to unmask]
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]]
Sent: Monday, March 01, 2010 12:52 PM
To: [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]>
To: [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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