PiStorm32-Lite and JLCPCB Soldering Issues

There is a lot going on right now about PiStorm32-Lite and the delays in production due to some soldering issues. We now know why this is happening, so I figured I would summarise for everyone what is happening and why things are delayed.

What is the PiStorm32-Lite?

The PiStorm was originally an accelerator for the Amiga 500/2000 which used a Raspberry Pi to emulate at very fast 68000 series CPU, whilst retaining the original Amiga chipset. I personally use this to help debug issues with Amiga hardware, but if you want bang-for-buck performance, it is unlikely to be beaten.

The PiStorm32 was a project to port this work to the Amiga 1200 and potentially other 32bit Amiga computers. This used a Pi Computer Module 4 (a special format for Raspberry Pi, typically more for commercial use) and a BGA FPGA. The problem with this is the FPGA is hard to solder and not really obtainable right now. Also with the Pi shortages it is easier to obtain a regular Pi right now. As such the PiStorm32 has not been released.

Along comes the PiStorm32-Lite. This is functionally similar to the PiStorm32, but uses an obtainable QFP FPGA (easier to solder) and supports regular Raspberry Pis (3 and 4 series).

The Problem

Once the design files were released to public, many people immediately went to order the SMD assembled PCBs from JLCPCB. To make things more compact so that it fits inside the Amiga 1200 a compact header is used with which the Pi slots through the PCB and into the connector.

When boards started to arrive, almost everyone found that the holes in the bottom of the PCB for this were full of metal balls. Especially orders on JLCPCB’s economy service.

Whilst this is annoying for many it is fixable by poking them out from the top with a pin. Claude, the original creator of the PiStorm, was getting pretty stressed about this and spent some sleepless nights trying to figure out why. He quickly put out a Twitter thread on how to solve this.

It was quickly discovered that the problem was excess solder paste which went into the holes at reflow time. Unfortunately in a few cases (such as the batch I’m working on), the problem is a little worse. Solder can get into the metal of connector itself, this cannot be removed easily. In my case I used a hotplate to remove the connectors, then the holes need poking in the PCB and will be replacing them with new ones.

The Cause

It took a lot of people talking to JLCPCB to get them to admit to the cause of this. I’ll try to explain this for those who don’t regularly order PCBs.

When you order PCBs you have a bunch of files in a zip file. These files explain to the fabricator’s machines how to make the PCB, each file describing a different layer. This includes the copper layers, the top and bottom masks (green coating), silkscreen (white printing), etc. One of those layers is the “paste” layer. This describes where to put the solder paste when you are soldering the boards, it is typically used to cut a stencil out which is then used to spread paste.

Now, it turns out when you get JLCPCB to assemble the surface mount components for you, they completely throw this paste layer out and assemble their own based on the components selected. This is where the problem lies, their template for the header used is incorrect, this means that too much paste was applied in the wrong places and when melted it went into the holes.

Recommendation

We recommend one of the following if ordering these boards from JLCPCB:

1. Contact them at order time to make them aware of this problem, with the hope that they will correct it (your mileage may vary, so far this hasn’t worked).
2. Do not get the boards with the connector assembled, solder them on yourself.
3. Using one of the more advanced services might be OK (not enough evidence yet).

We believe JLCPCB might have now fixed their template based on some communications, but have not been able to confirm this in reality yet. If you are affected you can complain and you might get some money back, but don’t expect a full refund or enough to cover the costs to put right.

Conclusion

If you are an end customer waiting for a PiStorm32-Lite. Please be patient, even if boards aren’t as bad as the batch I’m working on, it is still going to be a lot of work to fix them. Some orders are also delayed due to Chinese New Year.

Claude has been awesome throughout all of this, if you ever bump into him, buy him a beer. This is a fantastic board even if it JLCPCB messed it up a bit.