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How to make your own circuit boards

If you are toying with electronics you might want, at some stage, design your own circuit board. It is not very difficult. There are a lot of schematics available which could be used as the basis of a custom board.

This guide summarises my experience with different tools and methods. There are a lot of other tools available and probably better ways to come to the end result.

Step 1: Choose your PCB design software

PCB design software is used to draw the schematics, lay out the components on a board and to create the manufacturing files. I only looked at two free software packages. I personally decided to use KiCad.

Eagle

This is a very popular software package and runs on Windows, Linux and OS X. I think it is easier to use than KiCad but the free version is limited to one schematic sheet, 100mm x 80mm board and two copper layers. For these reasons I dismissed Eagle. If you can live with these limitations Eagle is probably the quickest to learn.


KiCad

KiCad also runs on Windows, Linux and OS X and is open source. It does not have the Eagle limitations and is definitely useful for quite complex boards. It also comes with a viewer for manufacturing files and a 3D viewer for your board provided you created the 3D footprints for all components first. The 3D viewing function is still a bit difficult to use but quite useful. You can for example export a 3D file of your board and import it into 3D cad software to design your custom case.

Compared to Eagle, KiCad is slightly more difficult to use. Some people don't like the fact that for example the schematic symbol is not liked to a component footprint. Once the schematic has been drawn you have to assign a footprint to each part. The advantage is that in order to change a footprint, for examples from a through-hole resistor to a SMD resistor, no changes to the schematic are required.

Step 2: Design your board

I don't want to go into details how to design circuit boards. The basic steps are:

  • draw schematic
  • assign footprints to parts
  • lay-out the board and route signals
  • create the manufacturing files

One of the bigger issues for the hobbyist is the footprint selection. Most people probably have soldered through-hole components. These days it is quite difficult to obtain integrated circuits in through-hole packages and therefore I would think it is pretty much mandatory to used SMD parts. The big question is how small can you go?

I had no problems assembling boards with 0402 (1mm x 0.5mm) resistors and ICs with 0.65mm pin spacing. These are very tiny parts. With 0.65mm pin spacing you are likely to get solder bridges across pins. This is easily fixed with de-soldering braid. At 1.27mm pin spacing solder bridges are unlikely.

Thermal pads on the back of the IC are no problem. I haven't used BGA packages yet but I like the idea of using them. The big problem with home soldering is to apply the correct amount of solder paste. With BGA packages the solder is already on the IC in form of small balls. Therefore this critical step is already taken care of and the only issues left are part placement and the correct reflow temperature profile. Although once soldered it is impossible to inspect the connections since they are under the chip.

The output of your design effort should be the following Gerber files (for a two layer board):

  • Top silk screen layer. This is the visible artwork on the top of the board. The layer is optional but recommended to reduce part placement errors.
  • Top solder mask. The board manufacturer will apply a solder mask according to the data in this layer. You can solder anywhere where there is no solder mask. I make the solder mask exactly the same size as the pads.
  • Top copper layer.
  • Bottom copper layer.
  • Bottom solder mask. On singe sided boards there should only be bare areas around through-hole pins.
  • Bottom silk screen layer. This layer is usually not required unless you intend to place parts on the bottom of the board which is not recommended for home manufactured boards.
  • PCB outline file. This layer should contain the outline of the board and any large holes or slots that are CNC routed.
  • Drill file. This file contains the location and diameter for all drilled holes for through-hole components and vias.

Step 3: Make the board

There are different options and manufacturers to get your board made. I used PCBCART and had very good results. You basically fill out an online form which defines your PCB and you get a quote straight away. If you decide to go ahead you upload the Gerber files and a few days later the PCB arrives via courier. In my case they even send me an email to clarify one issue.

One disadvantage is the relatively high set-up cost. For quantities of one PCBCART is probably not a good choice.

Step 4: Do I need a solder paste stencil?

The most difficult step in assembling a PCB is to apply the correct amount of solder paste. A stencil allows to “screen print” the correct amount of solder paste onto the board. This definitely makes sense for greater production volumes. For prototypes the expense is probably not worth it. It is definitely possible to solder 0402 components onto a board without a stencil. The thickness of the stencil dictates how much solder paste is applied. There are more durable metal stencils or laser cut plastic stencils available.

Step 5: Assemble the board

If you assemble the first board it probably makes sense to do this in steps. For example first solder all the power supply components, check if the power supply works and then assemble other components that create other functional blocks. Just remember as soon as you assemble through-hole components it is difficult to reflow afterwards. Through-hole components come last after all SMD components have been soldered.

It is also a good idea to start with the smallest components first and finish with the large ones. Without a solder paste stencil I apply the solder paste using a tooth pick dipped into solder paste. This way it is quite easy to apply tiny blobs of paste to the pads. Other people use a small syringe. I found that the solder paste keeps running even after I stopped applying pressure to the syringe. This is a bit messy and for me the toothpick blob method worked better.

I never ever applied too little solder paste to a pad. If in doubt apply less! Especially larger components encourage you to apply big blobs of paste to the large pads. Don’t do it. It is amazing how little paste is needed.

Check if all the components have been placed. Especially with 0402 parts it is actually difficult to see if there is a part on the pad or not. A magnifying glass would help but it is possible to do all this without one if you have good eyes. One of my next investments is going to be an USB microscope. These are quite cheap and they should be great for inspecting a PCB, taking pictures and movies.

Step 6: Reflow the board

I have only used the electric skillet method and I must say it works a treat for small boards. It is a good idea to first do a small test with a scrap board and some scrap parts to see how quickly the solder starts to melt. On full power it takes less than 2 minutes with my skillet which is a bit too fast. Recommended is about 3 minutes which can easily be achieved by turning the skillet heater off for a short period. With larger boards you might also encounter problems that some areas of the skillet are hotter than others. If you found a good set-up I would always place the board roughly in the same area to more reliably create the same results. If you have an aluminium plate or similar it would be great to use it as a heat spreader. Place the plate into the skillet and the board on top of the aluminium plate. Aluminium is a very good thermal conductor.

You don’t necessarily need a thermo couple to measure the temperature. Just use a stop watch and a test PCB to roughly melt the solder at the 3 minutes mark. Switch the skillet on and off until the solder melts at the right time. For example heat for 1:20, switch off for 20 seconds, heat for 1:20, solder melts, switch on and off for 10 seconds for a total of 1:30, switch off, wait 30 seconds, open lid to cool down. Something like this should give you a pretty good temperature profile.

Step 7: Check the board and fix solder bridges

Check the board for missing parts and solder bridges between pins. Solder bridges are easily fixed by placing a de-solder wick across the pins and heating it up with a regular solder iron. The wick sucks up the excessive solder.

Sometimes tiny parts float away because of too much solder or if the skillet is not horizontal. If this is the case I use a hot air solder gun to locally heat up the board to remove the stray part. With hot air it is also possible to reflow a single part. Remove any excessive solder using a de-solder wick, apply new solder paste, place the part and locally heat up the board using a hot air gun.

Step 8: Solder through-hole components

Most boards probably have some through-hole components. These are soldered last. Once pins stick out of the bottom surface it is difficult to reflow using the skillet method since the board floats on top of the skillet. Therefore ensure all reflow has been done before hand soldering.

Step 9: Power up and test!