# Manufacturing PCBs With Surface Mount Components

Summary: cheap ‘n cheerful, good enough for double-sided experiments, but not good enough for 4-layer impedance-controlled PCBs.

The laser toner technique and very-low-cost PCB manufacturers are good enough for the low-speed digital signals found in Arduino-class circuits. They are not suitable for large boards, or for containing medium speed digital signals capable of bit-rates up to 1Gb/ or 2Gb/s. A requirement for 50Ω or 100Ω differential impedance lines on >=4 layer PCBs implies the PCB cross-section “stack” must be tightly specified in terms the prepreg’s thickness and $\epsilon _r$.

This post outlines experiences for small experimental boards.

Also see my techniques for designing and assembling homebrew PCBs, and reference material.

## Laser Toner Transfer

I’ve used the traditional laser toner mechanism that’s described in many many blogs, but only for:

• through hole components on single and double-sided boards, with acceptable results
• gash test boards when experimenting with SMD components

This is acceptable for producing Arduino-class circuits with analogue and low-speed digital logic.

The results for SMD components are surprisingly good, and would just about be acceptable in an emergency.

## Hand-Milled

I’ve needed to make some quick-and-dirty RF 50Ω attenuators and 50Ω / 75Ω matching pads for use up to ~2GHz. These circuits consist of two edge-mounted SMA connectors and 1, 2 or 3 SMD resistors mounted on double-sided FR4 board in a “co-planar waverguide with groundplane” configuration. At approximately 15mm*10mm, these boards are small physically and electrically.

The track (singular) needs to be the appropriate width for the impedance. That can be determined with any of the many online calculators; I used Chemandy Electronics’ calculator.

The track can be made by using a hand-held Dremel to “mill out” the gap between the track and ground.

## DirtyPCBs

For small and/or experimental double-sided boards, I’ve used DirtyPCBs principally for cost, but also to have a benchmark against which I can evaluate a “real” PCB manufacturer. The principal features were:

• 10 off 5cm*5cm double-sided is \$14 (i.e £8-9) including sea shipping
• order placed to PCBs received: 21 days

which is remarkably good value.