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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