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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Stencil Apertures

Sal

#3645

Stencil Apertures | 1 July, 2000

I have two questions

1. How do I control the skewing of FETs/power regulators ? ( the one's with the big rectangular pad and two smaller one's for the leads).If I go 1:1 with the apertures I seem to get solder balling and when I tryed to minimise the aperture by using four smaller apertures ( window arrangement ) then I started to see skewing.

2. We've also recieved a product where the pads for the chip components are shaped in a D(mirror image ) type opposed to the normal square. What guidelines do I follow for stencil apertures to eliminate solderballing and skewing of these components ?

Any advice would be gratefully appreciated.

SAL.

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Ramon I Garcia C

#3646

Re: Stencil Apertures | 3 July, 2000

good morninrg Sal:

I think if you try with no windows shape, maybe if you redce 10% (5% per side ;5% one side & 5% other side, total 10 % )

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CL

#3647

Re: Stencil Apertures | 6 July, 2000

SAL, How large is the pad in relation to the solderable area on the component. I have seen similar instances where the heat sink of the component covered almost the entire bottom of the part. If your pad is the same size and the aperture is 1:1, there will be a very large amount of solder under the component. This causes the component to "float" for lack of a better term. I had to reduce the apeture in the stencil by 1/2 of the volume to eliminate this problem. I don't know if this is the same situation but it's worth looking into.

Hope this helps

Christopher Lampron

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