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I made a pcb with a QFN32 with exposed pad but I feel like I've made a mistake on the stencil, in the exposed pad area. I managed to solder it and the chip (CC1310) is programmed successfully but I'm still concerned about the stencil. The solder paste looks like a chess on the exposed pad and I don't think that this is the right pattern. enter image description here

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I am no expert, but it does not look bad to me. When you solder such a beast you want to be sure that all the pins will be properly soldered.

If you have less solder paste (per squared inch) for the EP than for the pins, when the solder will melt, it will try to wet the whole EP and will pull the QFN package, ensuring that all pins are close enough to their pads.

On the other hand, if you had the same amount of solder paste (or, worse, more for the EP) then you would have a chance that some pins are not properly soldered.

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  • \$\begingroup\$ I read once that the paste on the EP mustn't be on its boundaries, and maybe that is the reason I was concerned. \$\endgroup\$ – jgabcgr Mar 13 '17 at 20:02
  • \$\begingroup\$ Sorry for asking, but what is your point? I cannot guess why you feel concerned. But I guess the reason why you read that recommendation is the same reason why your stencil has this chessboard-like pattern: to ensure that there is not too much paste on the EP. \$\endgroup\$ – user2233709 Mar 13 '17 at 21:39
  • \$\begingroup\$ I'm asking if my stencil opening has good paste pattern on the EP and if I could add more paste even onto the tented visas. \$\endgroup\$ – jgabcgr Mar 13 '17 at 22:54
  • \$\begingroup\$ I don’t think you should add paste on the tented vias, as the paste won’t wet the solder mask. But I wonder why those vias are tented. That looks wrong to me. \$\endgroup\$ – user2233709 Mar 13 '17 at 23:02
  • \$\begingroup\$ Are tented in order to prevent the solder flowing through themselves. Do you believe there would be no problem if there weren't tented? Wouldn't the solder paste flow through the holes? And what if the chip moved slightly during the soldering process? \$\endgroup\$ – jgabcgr Mar 13 '17 at 23:09

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