Ever wondered how the pro’s physically manage to make a module? Well ok, you can get a fancy pick and place machine or send off for someone to assemble your module, but you can do it by hand. It is not as hard as expected.
As part of a .NET Gadgeteer hands on event at the Modern Jago in Shoreditch we were delighted to have Justin Wilson from Ingenuity Micro attend and show us how things are done (www.ingenuitymicro.com). He has designed and built an nice collection of .NET Gadgeteer modules and mainboards and expects to have them available shortly.
Justin has designed a multicolour LED module for .NET Gadgeteer, it is a 3 colour LED on a PCB with 2 Gadgeteer sockets. The module is nice as it is low cost simple and clean, and you can chain them together without the need for a co-processor on each module.
So the article title may be misleading, I really just got to assemble a module that Justin designed, rather than designing a new one. However after the assembly I felt I really had built something. (It was also amazingly good fun)
1) The first step is to design a PCB and get it printed, there are plenty of places that will produce PCBs and it is common to use EAGLE (http://www.cadsoftusa.com) to draw the schematics. Justin came along with a sheet of “Ingenuity Micro RGB Pixel v1.0” PCBs and all the components that are needed for the assembly. It is worth mentioning that some of the components are very very small, the black dot in the picture below is a NAND gate, it has a total of 5 pins. When you compare it with the Gadgeteer socket you can see that this could be a troublesome task. This PCB looks a bit rough as they were just snapped along the edges to separate them from the sheet.
2) The next step is to add some solder paste to each of the pads where we plan to solder components. There are two methods.
- The first is is to get a small screwdriver, or toothpick and put a tiny blob of paste on each and every pad that you need to solder components. This is very time consuming and can result in an uneven distribution of solder risking dry joints or bridging between pins. The workshop was over by the time I got to build my module so this was the method I had to use.
- The second method is to use a solder mask. This is a very thin piece of plastic (like a overhead transparency) with holes cut (usually laser cut) for all the points you want paste. The key is to align the mask up exactly with the PCB and then in one go spread the paste across the top. It is handy to make a holder to align the PCB and mask, as shown below. Wherever there is a hole in the mask, solder paste will be deposited. Be careful to remove the solder mask cleanly in one move so as to not smudge the paste that has been left behind. If you have the correct solder mask, the correct way round you will end up with every pad on the PCB nicely coated with solder paste. (EAGLE can produce solder masks: http://www.cadsoftusa.com , and there are companies that will laser cut your EAGLE mask out of plastic)
3) It is easiest to place all the components on one side of the PCB in one go. Be sure to place all the components the correct way round! The RGB Pixel only has one component on the top, an SPI LED with 6 pads, which is nice an big, so easy to place. Check to see that all the pads/pins are correctly aligned and that there are no bridges of paste between pins. Don’t worry too much as the solder and flux will pull the component into place a bit.
4) Once all the components are in the correct place, it is time to heat the board. Some people use an oven, but as it was a workshop it is easier to use a Hot air rework station (basically a very hot air blower) they are amazingly cheep and I got one from Amazon, not too sure how long it will last, but cant complain as it was a real bargain. The hot air station goes up to 450C which is enough to burn almost anything! I run my one at 250C but check to see what temperature your paste recommends. Also you might want to check the maximum temperature tolerance of your components. The picture below shows the LED being heated, the solder starts gray and paste like, but when it comes up to temperature it will quickly flow around the pins/pads and collect in all the places you wanted it to be, just like magic. It will go silver and shiny when ready.
5) Next step was to do the other side of the PCB. This was more complex as there are 2 capacitors (C1,C2), 1 resister (R1) , 1 NAND gate and 2 Gadgeteer sockets and they are all really tiny, the paste helps hold them in place. (Completed module below)
6) The next step is to test the module, and write some software. If you are writing a driver for a new module, be sure to follow the module builders guide http://gadgeteer.codeplex.com/releases/view/105388
Justin provided a driver for his module, so it was just a case of testing the various methods. There is a code sample below.
Fantastic it worked !!! (Trying not to be too surprised) The module is great, you can chain multiple together and they are very bright! Check out the colours below…, it is a multicolour LED with 0-255 for each colour, resulting in a possible 16million different colours.
Love Electronics USB DC Power Module:
GHI FEZ Cerberus:
RGB Pixel : Ingenuity Micro