Solder Coverage in Non ROHS Paste

1 to 1 stencil aperture to pad should be fine on the gull leads, and yield 100% coverage with leaded solder. The thermal pad is going to be a challenge though, if you truly need 100% coverage. There will be out gassing from the flux and this will need a path to escape from under the component. Window panes provide a path for outgassing, if you aren't using those, you will risk getting large voids under the component. If the thermal pad is small enough, you might be OK not using window panes.

First step would be to talk to the component manufacturer. Do you really need 100% coverage, and what stencil design to they recommend? After that, you might have to experiment with the stencil aperture design. You could also talk to your paste supplier and ask about low voiding solder pastes. they should also be able to give some advice on the reflow profile. X-Ray will be your friend for this process.

Finally, assuming heat transfer is the goal, you could look at the pad design. Adding vias to the pad to help shunt heat to the other side of the PCB.

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What is your current paste coverage? You mentioned windowpane and you mentioned 5mil stencil. You did not mention if PAD design meets recommendation? If it does, go 6mil and more paste coverage to increase volume.

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OSP finish is the big issue here. You almost can not get 100% coverage solder on OSP with 1 over 1 aperture stencil. Reconsider solder coverage requirement in this case. Check your peak temp in profile may help a little.

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Hello Jinesh , if you can provide us with component datasheet , stencil design vs PAD design (GBX) and the thermal profil you use.. It would help us to found out the issue and help you.

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You likely have raised belly pads. If possible, do a step-up on the thermal pads to compensate for the additional height of the component in this area. Some reduction/adjustment of the gullwing pads may be necessary, so be prepared for a few iterations of the design.

Also, 100% is never a realistic goal. If this is required I would push for an explanation/adjustment/reevaluation of the design.

One other thing to consider is whether or not there is a mis-match between the sizes of the board pad and component pad. If there is a mismatch, you should ensure your x-ray inspection is using the appropriate pad size to accurately determine coverage.

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