Building PCB Assembly Prototypes

Part Organization

When designing printed circuit boards, it is necessary to build prototypes for testing. The process must be as efficient as possible so that we can iterate faster.

For complex PCBs, you are probably best off having your production PCB assembly company assemble them.

For smaller PCBs, it may make sense to have a company like Macrofab, SEEED, JLCPCB, PCBWay or one of the many other companies assemble them.

It is also possible to assemble smaller PCBs yourself, and that is the topic of this thread.

We have recently been building prototypes for several PCBs for a customer. PCBs are cheap and easy to order. Parts are easy to order from Digi-key or Mouser by uploading the BOM. What is not simple is organizing 100 different parts in the lab so that you can easily organize and find them over time.

Ideally everyone would use the GitPLM semi-structured part number format. But, lacking that, we are currently organizing parts using the manufacturer part number (MPN).

We group the parts in 4 groups:

  1. Misc parts with MPN starting with a digit
  2. Misc parts with MPN starting with alphabetic character
  3. Capacitors
  4. Resistors

Parts in each group are sorted numerically/alphabetically by MPN.

We then organize the BOM into these 4 groups as well.

Highlighting the MPN on the bag also makes it quicker to find/compare the number.

Then it is an easy matter to go down through the BOM and parts box sequentially to assemble the board.

Long term, I would like to be able to assign GitPLM IPNs to every part in the lab and track inventory in GitPLM or ODOO MRP.

It will be much easier to find and compare part numbers if the BOM and part bag have GitPLM IPNs as shown below:

Solder Paste with a hot-air gun

TLDR – get a stencil!

Assembling prototypes with solder paste can be quite a bit faster than hand soldering every joint. The first time we tried this, we just used a syringe to put down a bead of paste on the pads like the YouTube videos show. We did get some bridging under the chips as we probably put down too much paste, or perhaps did not heat the board hot enough:

(sorry about the poor focus)

For the next prototypes, we ordered a stencil and applied the paste with a plastic card. This worked much better:

Below are some images of the applied paste:

Alignment was not perfect, but the result was much better – only one bridge on the entire board with some fairly fine-pitch parts.

We are using an ATTEN ST-862D Hot-air rework station with a large nozzle to reflow the paste. It only takes a couple of minutes with a small board and works pretty well, so it seems a reflow oven is probably overkill for now until we get to BGA components.

Not perfect, but much better than hand soldering each joint:

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Pixel Pump An open-source, manual pick-and-place machine for PCB artisans

Interesting product:

One neat accessory they offer is a magazine for easy dispensing of SMD parts: