Steve,
I use round pads to decrease pad size (increase circuit density). A side benefit seems to be less chance of skew, I don't have numbers on tombstoning/drawbridging, but product hasn't yelled. I have also been tinkering with the idea of other geometries just haven't come across the right application yet.
Dan
----- Original Message -----
From: [log in to unmask]
To: [log in to unmask]
Sent: Tuesday, April 09, 2002 8:12 PM
Subject: Re: [TN] 0402 tombstone problem
I just heard something not too long ago, that round pads for 0402's are the way to go.
Never heard of that before, but just recently received a board for quote that uses round pads for the 0402 components...anybody else ever heard of this?
Guess I'll find out how it works inna little while, while pondering why a round pad would work better than a square pad....
-Steve Gregory-
Edward,
When we do everything correct on 0402 and 0201 and still have components
standing-up, we often look to the component terminations and find poor
plating.
Good luck
Dave Fish
----- Original Message -----
From: "Edward S. Wheeler" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, April 09, 2002 10:59 AM
Subject: [TN] 0402 tombstone problem
> Hi folks, we are running a new board with 0402 parts on it. It seems that
> we are having a tombstone problem as well as a problem with parts not
> staying centered on the pads. We are currently using 20 mil square pads on
> the board, with 20 mils of spacing between them. Our stencil is 6 mils
> thick, laser cut and electro polished. The trapezoidal walled apertures
are
> slightly reduced, 17 mils square, and centered on the pads. It appears the
> chip shooter is placing the parts perfectly. We are using eutectic solder
> paste with an OA flux, and reflowing the parts using the recommended
profile.
>
> Are there any suggestions any of you might have concerning this size of a
> part? Is there a better stencil design, reflow profile, or pad design that
> could help us out? I would appreciate any suggestions.
>
> Thanks.
>
> Ed
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