Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


fine pitch on thick copper

pascal MATHIEU

#8112

fine pitch on thick copper | 20 December, 1999

hello guys ; we are using a fine pitch component(0.65mm) on a thick copper PCB (Cu = 90�m) ; in this case we notice that we are in the process'limits , because the different supplier of the PCB are not able to ensure a good stability of it's process specially for the small pad used for the fine pitch component : the result is lack of solder or bridge solder so quality trouble . i am waiting for some experience about this topic ,the result you have , the eventual alternative ; i am opened to have a chat about this critical point . bye , bye have a good christmas

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#8113

Re: fine pitch on thick copper | 20 December, 1999

Hi Pascal,

0,65mm pitch normally isn�t much of a problem. With 90�m CU I don�t have any experience but would like to know what deviation from nominal value for the pads you get with different PCB-deliveries. In short, for the standard Cu=35�m we see in almost all cases a reduction from nominal width of about -10%. This results in stencil aperture reduction minimum the same amount with satisfying results. In your case I would try to determine the worst minimum deviation and adjust my apertures to that. If that reduces the amount of paste to much go for a thicker stencil. Another question is, have you checked your process according to fine pitch with normal PCBs and do they run without trouble. I know paste printing is the key to success in SMT and you have to work on it but try to get your supplier in the workflow, what can be done to get this specialty more stable, try to choose the one who is the most stable.

M2C

Wolfgang

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GERARDIN

#8114

Re: fine pitch on thick copper | 21 December, 1999

Hello Pascal

As mentioned by Wolfgang the key issue is the printing process capability. For a thick copper level 90�m we noticed that the pad reduction can be greater than 20% depending on supplier sources.

Typicaly for a cad Width = 0.4 we can get 0.3 to 0.34 on the top of the pad. This will be critical in term of printing but also in term of placement (connection width distribution =0.28 to 0.35).

Kind regards

PASCAL

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