Starting a hardware company is a daunting task. Not only are prototype device builds time consuming and expensive, but you often need to change the design many times before you are satisfied with a product you can ship. This problem is multiplied when you’re presented with a complex design challenge that is breaking new ground. This is a challenge that unfortunately can prevent many hardware start-ups from getting off the ground. For Thalmic Labs to realize the final Myo™ armband design, it took many, many, PCB (Printed Circuit Board) prototype builds before the hardware team was happy with the end product.
My name’s Zack and I’m a Hardware Engineer here at Thalmic. The guts of a modern electronic device are generally mounted on something called a printed circuit board, or PCB. A PCB consists of layers of copper traces, which act like wires, connecting the various components that make up the design. Components are items such as resistors, capacitors, and integrated circuits. When you want to assemble a prototype, or a final production device, one of the steps is attaching all of these components to the PCB. Sometimes, this process can be accomplished by hand soldering for simple designs or small numbers of prototypes. However, this makes it difficult to control the quality of the builds, and often the assembly process takes a very long time to finish. For this reason, we build most prototypes using automated assembly lines.
These assembly lines, also known as SMT (Surface Mount Technology) lines, allows design teams to very quickly place and solder components onto panels of bare PCBs. This allows for full control over the build and lets designers watch prototypes assemble right from the comfort of their own desks.
Stage One, responsible for spreading the solder-paste.
The SMT line is a very complex and interesting machine. It operates in a few stages that flow together to create a final assembled PCB product. The first stage is where solder-paste is deposited onto the bare PCB panel in areas that are specified by the PCB design engineers. By laying a stencil over top of the panel and spreading the solder-paste so it only reaches the exposed areas, the solder-paste is spread on copper “lands”, which are areas where components will be connected to the PCB.
Stage Two. The ‘pick-and-place’ area.
Once this is done, the PCB panel is placed into a “pick-and-place” area (also known as a chip shooter), where tiny nozzles fly over to reels of components, pick a number of them up at a time, and very accurately deposit them onto the areas where solder paste was spread.
Stage Two. The reels holding the components.
Finally, the PCB panel is passed into a “re-flow oven” where the entire panel is exposed to very high temperatures, following a strict profile which melts or “flows” the solder paste and connects the components to the PCB in a semi-permanent fashion.
Stage Three. The re-flow oven.
Not only are Myo™ prototypes built using a process similar to the one described here – production devices are built the same way. This means that the work we do experimenting with and tweaking the assembly process during the prototype phase carries over to volume production, and we’re able to apply many of the learnings to delivering more robust hardware in the end!