Jeremy Rubin's Blog

Here you'll find an assorted mix of content from yours truly. I post about a lot of things, but primarily Bitcoin.

categories: Bitcoin, Shenzhen Journey.

PCB Factory Tour

Shenzhen Adventure Day 4

First they hand check the design to conform with their capabilities. They will make minor changes if necessary.

Next they drill out any holes needed in the boards. They very frequently check the bit quality, and bits are only used for 3000 holes before being swapped out.

Next they do some electroplating stages

Here they do the photo chemical processing steps that are light sensitive

Then they do silkscreening (I’m missing a picture of this…)

Next is depanelization, or cutting out the individual boards from the panel.

Finished boards

Next they have Quality Control:

  • Chemical checks that boards have the correct properties

Inspecting the boards quality visually, they cut out a chunk of board, encase it in resin and then grind it down to the edge

They also digitally check every single board for continuity/impedance.  This machine essentially has two needles it touches between each point to test,

Injection Mold Factory Tour

Shenzhen Adventure Day 4

At this place we got to see them designing and making the molds. This was pretty crazy to me! Basically you can 3D-model your part and then ship it to them and they design a mold around it which has all the mechanical parts needed to make the mold. Once the design is there, they will CNC mill it out roughly. For finer details, they will do what’s called Electric Deposition, where they use a finely CNC’ed copper electrode in the mirror image of the design and repeatedly tap it onto the mold with a massive current running. This eventually cuts out the design layer by layer by blasting away the steel and copper.

Injection Molding Factory Tour

Shenzhen Adventure Day 4

This was fun! At the injection molder they had a massive pile of not being run molds

and about 20 machines which were cranking out parts. We got to see our mold for the class pried apart which was cool.

Molds are super complicated; I didn’t have an appreciation for how hard they are to make before.

Here’s a run down:

  • Tolerances are ridiculous. They need to be airtight metal with no gaskets so that the plastics don’t leak
  • For nice looking parts, the molds need to be basically mirror finish.

  • Molds can be made from Aluminium for lower cost but they basically don’t do it in China because Steel is cheap enough there.
  • A mold will run about $5000-$10000 USD for a reasonably sized design, and can do about 500,000 casts. This is mostly the price of the steel
  • You can modify your mold by welding on a block of steel and then re-carving out the features
  • Designs with overhangs or other features are much more complicated to build because the mod needs to essentially unfold itself to be able to release a part
  • A mold has a couple key properties, the points where the pins push the cast out and the fill points. Based on these, the finished product will have different flows of plastic through it which could cause different knit points (where two flows meet) or flow lines (artifacts of the plastic’s path). The points where the pins push out are those raised disks you sometimes see on plastic objects.

Day 4 Overview

Shenzhen Adventure Day 4

Today (Day 4) was awesome, we toured various manufacturers to see the “end to end” development of a device. I’ve broken out the blogposts on each factory separately.

Lunch: We went out to lunch with some of the guys from one of the factories to a local place. The food was great, but a little unfilling as all I had was plain veggies. Luckily, I decided to keep a jar of peanut butter with me at all times so I had a couple spoonfuls in the car for protein. I was most intrigued by eating Gingko in a dish. It’s a kind of “creamy peanut” texture, with a potato-y taste. There were also these guys sitting near us who had the most incredible raspy voices, they were speaking an unknown local dialect and were basically shitfaced at noon.


Jon Lee rejoined us for dinner which was awesome! Of course it meant getting somewhat inebriated again (this time, baijiu and budweiser bombs). Again, they made sure there were plenty of options for me to eat which was great! The restaurant also had these amazing pots of tea, I drank a large volume of that. I was particularly excited to eat a whole water chesnut (never seen them not sliced).

Small Bootcamp Update

Shenzhen Adventure Day 3

Today was mostly an “in house day”.

We had a lecture from Bunnie on the course and then we worked on getting our dev environments set up.

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