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Struggling with soldering PG-TSDSON-8

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tooki:

--- Quote from: wraper on November 16, 2021, 09:59:51 am ---
--- Quote from: tooki on November 15, 2021, 10:18:28 pm ---
--- Quote from: wraper on November 15, 2021, 10:08:51 pm ---When you get solder sucked into via, part gets pulled towards pcb in that patricular location. Which may cause solder squeezing out in other locations without vias where solder has no other places to go to.

--- End quote ---
To be very clear, it’s not that the via is sucking the chip down, it’s that the excess solder on the other pins is lifting the chip up. I say this because the same effect happens whenever you have excess solder on a pad, even if none of the pads have vias.

--- End quote ---
Yes it is sucking the chip down with almost zero distance to PCB left due to surface tension/capillary action. If there was no solder paste at all on the pad with via to begin with, chip would sit straight, holding on other pads. It's not an excess solder, it's almost no solder on the pad with via what causes the issue. Once the part does not sit straight due to lack of solder on some pad, then you likely will also have solder squeezing out from some other place.
https://www.eurocircuits.com/pcb-assembly-guidelines-solder-escape-wick/

--- End quote ---
:palm:
The same effect happens with no vias around.

Let me repeat this: you get the same thing with NO vias. It IS the excess solder that causes lopsidedness. (Even if all pads have even solder distribution, if the solder amount is excessive, then you get chips floating around and cooling crooked.)

It’s not the via pulling down, it’s the excess solder pushing up. “Almost zero distance to the PCB” is precisely how a good joint is supposed to be. Surface tension and capillary action  apply to all solder joints, it’s nothing unique to a via.

T_guttata:
I posted a picture where you precicely see, how much solder there is. Is this really too much???

uer166:
I would start by ditching the low melting temp solder, I've had serious issues with it like lack of wetting (just like in your case), and serious outgassing of the flux post-soldering ruining conformal coats. I would recommend Kester EP256, easy to use and wets really well. Based on your pictures, there is too much paste (try thinner stencil), but nothing too bad, so just try switching paste.

T_guttata:
Ok, this Kester EP256 is not available on digikey. But I will try another paste with Sn63Pb37.

uer166:

--- Quote from: T_guttata on November 16, 2021, 08:29:38 pm ---Ok, this Kester EP256 is not available on digikey. But I will try another paste with Sn63Pb37.

--- End quote ---

It's available on Amazon. I can't comment on normal Sn63Pm37 paste, but EP256 was specifically designed to be easy, and it shows.

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