Struggling with soldering PG-TSDSON-8

[tooki]

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.

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.

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/

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]

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

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

[T3sl4co1l]

That particular attempt looks fine, yes.  The solder balls aren't great, and it's not clear how much wicked into that via (evidently not much). That might just be process variation.  Doing another dozen or so would give, at least a starting point, as far as statistical samples go.

Tim

[tooki]

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

I think so. But it’s easy to test: stencil it on, then use a curved scalpel blade to carefully remove some paste before placing the component. For example, try removing 1/3. Then see how it reflows.

Since you have a microscope, you don’t need to rely on a full fillet on each pin to ensure it’s connected: use the microscope to look at the joint from a diagonal. You should be able to see whether it’s flowed to the pad and pin.

[T_guttata]

I tried again with a different solder paste, but unfortunately it does not really look better?

I don't have a scalpel blade to try to remove some solder. The stencil was way more expensive than the actual PCB and therefore I would assume, that it actually works.

What's usually the thickness of the stencil? Maybe jlcpcb does not a good job in this regard?

Anyway, I will certainly switch to a LFPAK56 footprint. I want to be able to solder it correctly with 99% chance, otherwise I only end up debugging.

Maybe I could also order a fully assembled PCB from https://www.eurocircuits.com/? I just did not find any price indication for assembly.

[tooki]

I tried again with a different solder paste, but unfortunately it does not really look better?

I don't have a scalpel blade to try to remove some solder. The stencil was way more expensive than the actual PCB and therefore I would assume, that it actually works.

What's usually the thickness of the stencil? Maybe jlcpcb does not a good job in this regard?

Stencils are intended for precision application in multi-thousand-dollar paste printing machines. They were never intended for manual use. Chances are you think you’re using it properly, but aren’t. (Using stencils manually is HARD. I was just talking about that the other day with a guy at work — a literal graybeard who started working in electronics before I was born — because of some difficulty he was having with getting clean paste prints for some components. And that’s with expensive European-made boards and stencils. It’s very hard to support a stencil properly when using them manually. They need high rigidity by being mounted into frames under high tension, not flopping around.)

Tiny parts with tiny pads simply leave no room for error. The tiniest slip and you get paste under the stencil, which raises it up and increases the amount of paste applied.

Honestly, the last picture there doesn’t look bad at all. But yes, if a larger package is available and PCB space allows, use it, as it will make your process more predictable and easier to inspect.

FYI, with JLCPBC stencils, the vast majority of the cost is shipping, due to the dimensions of a whole stencil. But you can apparently ask them to cut the stencil down to size for manual use, allowing it to be shipped in the box with your PCBs.

[T_guttata]

I was looking for very low Rds_on mosfets smaller than the TO220 package and ended up with this PG-TSDSON. The TO220 package would be too big, but the LFPAK56 is 5x6mm and totally fine. I will try it.

Stencils are intended for precision application in multi-thousand-dollar paste printing machines. They were never intended for manual use.

I doubt the package size of 3x3mm was designed for hand fabrication^^

FYI, with JLCPBC stencils, the vast majority of the cost is shipping, due to the dimensions of a whole stencil. But you can apparently ask them to cut the stencil down to size for manual use, allowing it to be shipped in the box with your PCBs.

Yes, I already reduced the stencil size until it does not increase shipping chost. $2 for 5 PCBs, $7 for the stencil and approx $20 for shipping^^