I am not sure why you'd want to fill the vias.

However, maybe it's worth a try. Everyone always insists that they will wick solder away through capillary action. However, on the internet, everyone will generally just repeat what one person stated somewhere, often wrong. Pretty much everyone says that you can't do BGA at home, you need an X-ray machine, you need solderpaste, etc.

First of all, make sure it's worth the trouble. You can only pass one wire between the pads anyway using 6mil wires - anything smaller will cost a lot. So if you drop too many connections to the bottom with filled vias, you won't be able to route them out anyway. You may find that it buys you nothing.

So let's say you want to fill the vias. First, you'd have to make sure there is no soldermask. You'd have to do add a 'filling' step prior to placing the BGA. To apply an even amount, you can either float the board on a layer of molten solder and let the wicking action pull solder into the vias. Alternatively, you can apply solderpaste and let it get sucked in.

I'd go with solderpaste - it seems more precise. Maybe from the bottom. You will need a lasercut mask with really small holes. Then you will have to make sure that the surface is even - if some balls don't touch the surface because they are raised, they may not make proper contact.

Once again, I certainly would not do this - I've lost enough 700ANs already Pretty soon I'll start a 'reballing' thread...

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In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

I haven't tried vias in BGA pads, but I've tried vias in/near regular 0603 pads, and I can assure you that they do suck up the solder paste to the point where the joint becomes unreliable. I imagine it will be the same for BGA.

This is without filling in the vias prior correct?

I'm thinking first of all, via's under a ball would be great direct connection for the power and ground pins to the power and ground planes.

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65Org16:https://github.com/ElEctric-EyE/verilog-6502

Correct. For regular components it's easier to inspect the joints afterwards, and add some solder to the bad ones.

The first couple of my attempts were along these lines (I thought I'd need some solder on the pads). None of these boards worked (for various reasons, some without an explanation).

I was really concerned with invisible shorts or other damage to the board made while dragging and wicking solder. Since the remaining solder residue is not perfectly distributed, some balls get more than others, so you'll never be sure if they all get soldered down.

I really like my final approach; I am absolutely sure that every ball has exactly the same environment and don't expect any trouble from the connections - and I would never make any bets on boards made after dragging and wicking solder. I am pretty sure that I will never touch the pads again with anything other than balls.

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In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Here is a close-up of a failed board with a little resistor for scale. You can see the power distribution buses under the mask, and get a sense of the vias. Note that on my board I did not need that many IOs - I connected an SRAM and every pad of the 6502, a 44-pin connector (a few pins for power) and two 'butterfly' connectors with 4 extra IOs, and have a dozen spares connected to tiny pads. All using the top layer. Only a few special connections (JTAG, power, clocking, configuration) are routed to the bottom.

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In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

So oshpark's via's look like they do have soldermask over them?

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65Org16:https://github.com/ElEctric-EyE/verilog-6502

You could do mask or no mask, it's up to your CAD package. The post sockets in the upper left are just big vias.

EDIT: I think they call them 'tented' vias if they have a mask.

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In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Oh OK. BTW ExpressPCB is very competitive. Their 4 layer ProtoPro board service for a 21sqin board is $195. You get 4 boards. Their via's are not soldermasked. You do have to use their free software though. I like it and have grown used to using it.

EDIT: Permit me to show off my video board to show their quality. I should have added it to the thread a long time ago. It's at the very bottom of the first post.

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65Org16:https://github.com/ElEctric-EyE/verilog-6502

Slighltly OT: Can Express PCB do unplated holes with pads on either side?

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In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Unsure what you mean. Can you draw a pic or something?

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65Org16:https://github.com/ElEctric-EyE/verilog-6502

I mean just a drill hit, without plating. This would have to be a second drilling pass after the plating process is done, and Oshpark's fab does not do it.

I happen to need drill hits piercing pads on top and bottom, without electrically connecting them.

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In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Ah. No, ExpressPCB doesn't have provisions for this either in the board layout program.

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65Org16:https://github.com/ElEctric-EyE/verilog-6502

Also known as NPTH, Non-Plated Through Hole.

Back to BGA mounting, in an oven. It's not possible to mount devices simultaneously to the top and bottom of the board is it?

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65Org16:https://github.com/ElEctric-EyE/verilog-6502