PCB manufacturing and assembly at Elecrow in China

I’m an inventor and regularly make electronics prototypes. A customer drew my attention to Elecrow, here you can get high-quality PCBs at a lower price.

For example, a double-sided PCB of 10 x 10cm costs less than $10, including shipping. You will get always five pieces, even though you only need one. The PCB is completed with a solder mask and a silkscreen on both sides.

Before, I used more often perfboards, because manufacturing single PCBs was expensive:

Delivery time

The cheapest delivery time usually takes about 2½ weeks. For an additional charge you can get it faster, but for me, the delay is not a problem. It’s a hobby, in the meantime I can work on other running projects. Also electronic parts have to be ordered, which takes time till they are arrived too. If software is needed, you can also start writing it.

Buidling multiple prototype versions

In the case of mass production, you have to repeat building new prototypes until the last version is faultless and can be produced. However, building too many prototypes can exceed the development budget. Because at Elecrow, a prototype PCB is cheap, I built four prototypes of my spot welder PCB before it went to production.

Making the first prototype PCB

The first prototype PCB can be designed quickly and sloppily. It is not necessary to spend time on aesthetics, it often has to be completely redesigned when many things change. During the development process you always get new ideas and insights. Designing fast and sloppy is however quite difficult for a precision neurotic as me.

PCB Assembly at Elecrow

Here is an example, the SAM 15x15, an Arduino Zero compatible SAMD21 board:

The first series were manufactured in the Netherlands. Due to the fairly high production costs, the sales price was $24.95, which was too expensive compared to similar Arduino boards. Because the SAM 15x15 is now manufactured at Elecrow, I can sell it at a lower price.

Elecrow has a list of free SMD components, you only pay the assembly costs. These costs simply depend on the quantity of pads, $ 0.03 for SMD pads and $ 0.04 for THT pads.

How to choose PCB trace width and via size

These are the most important Elecrow minimum values

Incidentally we may need a smaller trace width of 4mil, e.g. under ball grid chips.

PCB trace width and via drill examples

• Samsung GT-S5660 smartphone: Trace width 2mil, via diameter 12mil
• Acer laptop 2008: Trace width 4mil
• Sparkfun-samd21-mini-breakout: Trace width 10 and 6mil, via drill 10mil
• Arduino-Zero-Pro-V3: Trace width 16 and 8mil, via drill 16mil

How to choose resistor and capacitor SMD size

• 0805 Very large and is not used much anymore.
• 0603 The most used, also in laptops, except in smartphones. The advantage is the low assembly costs. You can still solder this size manually.
• 0402 The most used in smartphones because of miniaturization.
• 0201 This size is sporadically used in smartphones.
• 01005 I have never seen this used.

Note that the assembly of very small SMDs is more expensive.

PCB checklist

• Carry out the Design Rule Check.
• Check unconnected pins. In Eagle file > export Pinlist.
• No traces under crystals and TO220.
• Large pads for components that may need to be replaced.
• Check if the Gerber files contain all layers, don’t forget Tdocument, Bdocument in Eagle.

Silkscreen text checklist

• All text is vector
• Pin1 at ICs, connectors and jumpers
• PCB name and company name
• Date or version
• TS and BS
• Name test pins

Online Gerber Viewer

Here you can upload the entire set of Gerber files in one go and see how the PCB looks like:
https://gerber-viewer.easyeda.com/

Adding breadboard pads

I always place extra pads on a PCB, that allow easy modifications afterwards. Use a dummy via: square 42mil, drill 20mil. Delete the via-solder mask, in Eagle you can do this by: Edit> change> tStop> on / off and then select the via.