Kane,
Related with flatpacks we had this experience in the past, like Steve said
you need special land patern with solder thieves and 45 degrees orientation
related with solder wave. Another critical factor is the chip placement,
glue atachment is not so good as solder paste before oven, so if the board
has a fast desaceleration ( handling, machine exit, conveyors speed, etc )
the chip can be moved away from center position and bridges will happen.
Another issue with flatpacks on bottom side is rework, be careful with
stronger glue after cure, because if you have to remove the component will
be very hard and can damage the board.
Unfortunally I don`t have the land pattern design ( I had this experience
at another company ) to send you ...
Thanks
> -----Original Message-----
> From: Kane, Joseph [SMTP:[log in to unmask]]
> Sent: 19 de Abril de 1999 19:24
> To: [log in to unmask]
> Subject: [TN] Hot Air Knife
>
> TN'ers:
>
> We're getting a handful of bridges at wave solder on a few designs. We've
> tried A, B, and C, but they continue to show up consistently on some
> styles
> of connector behind chip components, and on trailing leads of flatpacks.
>
> The machines is a fairly new Electrovert with convection preheat, Lambda
> wave, and chip wave. We're using Sn63 at 500F with RMA 25%.
>
> We're looking at a hot air knife retrofit, which would be turned off on
> everything but problem boards. We've had a demo, with mixed results.
> Good:
> bridges were much improved, and no insufficients. Not-So: some frosty
> looking joints, which we expected, but also a lot of solder balls and
> splashes.
>
> We've heard that setup can be touchy, and we didn't expect to optimize on
> a
> two board sample, but we're not sure what we can conclude here.
> Unfortunately, the demo was not apples-to-apples - it was performed on an
> inerted machine with an A-type wave, and we're not sure if the splashing
> and
> balls could be attributable to the increased surface tension.
>
> Anyone out there have good things to say about their hot air knife?
>
> Joe Kane
> Lockheed Martin Control Systems
>
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