Manufacturing circuit boards is a process that takes time and is not considered a 'simple thing' to do. Although, there are enthusiasts who are able to make their own boards at home with the right materials, but they usually tend to be not as complex as machine made ones. Also, it would be pretty time consuming to hand make 20,000 PCBs. Below, I will briefly walk you through the PCB Assembly process and what is involved at each stage.
PCB Assembly, which is also known as Printed Circuit Board Assembly is when you solder electronic components to a PCB or printed circuit board. A circuit board that has not yet been assembled with the electronic components are called PCB or Printed Circuit board and once the boards have soldered components on them, they are technically referred to as Printed Circuit Assembly or Printed Circuit Board Assembly.
Keep in mind that circuit board assembly is not necessarily the same as circuit board manufacturing. When you manufacture PCBs, it involves multiple processes that include PCB Design and actually creating the PCB prototype. Before the board can be ready to use in electronic equipment or gadgets, the correct components need to be added by soldering them on. The type of components and the process of the assembly depend on the type of circuit board it is, kind of electronic components that need to be connected, and what electronic device the board is going to be added to.
So, after the PCB is done being made, it is time for the various electronic components to be attached to it in order for it to actually be functional. This is sometimes referred to as PCBA or Printed Circuit Board Assembly. There are two types of construction methods used for the assembly.
1) Through-Hole construction: Component leads are inserted into the holes2) Surface-Mount construction: Components are placed on lands or pads on the outer surfaces of the PCB.
However, in both construction types, the component leads are still electrically and mechanically fixed to the PCB with molten metal solder.
Depending on the volume of boards that need to be assembled will determine how the components are going to be soldered. If it is for a high production volume, then soldering components to the Printed Circuit Board is best done by machine placement. Machine placement is done with bulk wave soldering or reflow ovens. Otherwise, if the production quantity is for small volume prototypes, soldering by hand works just fine in most cases (Ball Grid Arrays are actually impossible to solder by hand).
Often, through-hole and surface-mount construction has to be performed in one PCB assembly because some needed electronic components only available in through-hole packages, while others are only available in surface-mount packages. Also, it is a good reason to use both of the methods during the same assembly because through-hole mounting can actually provide more strength for the electronic components that are likely to go through some physical stress. If you know that your PCB isn't going to go through any physical stress, then it can be more wise to use surface-mount techniques in order to take up less space on your board.
After the components have been fully constructed on the PCB, it is always best to test to make sure that the board functions correctly and to the performance needed. Here are some of the ways that they are tested after they have been assembled.
1) A simple visual inspection to make sure that there are no electrical components out of place on the circuit board. It is also a good time to double check all of the soldering. (power is off)2) Analog Signature Analysis: when you applie a current-limited AC sinewave across two points of the electrical components and circuit. (power is off)3) Performing an In-Circuit Test: checking various physical measurements with the board like voltage, frequency, etc. (power is on)4) Performing a Functional Test: verifying that the circuit board actually does what it is intended for. (power is on)
If some of the printed circuit boards fail any of the above tests, not all is lost. You are able to find out where the problem is happening and replace the failing components and/or board to allow for it to pass. This is sometimes referred to as reworking.