Before introducing how to perform the functional test after pcba processing, it is best to understand how it was performed in the past. The best way to understand the actual test is to visit the PCBA manufacturing plant that produces products similar to yours, and view the entire production line, from the board to the workshop until the product is packaged and shipped. The secret of this is that we can actually experience the various processes of the product in the production process, which is very helpful for us to understand how the circuit board is produced. So today we will focus on analyzing the related issues of functional testing:
1. Functional Test Plan
Before the SMT processing of a circuit board, there is usually a DFM instruction book during the design process. This will put you in the time planning of “design for testability” throughout the design process. It will clearly state which test aspects are included in the schematic, PCB layout and even the microcontroller code. For example, if a user touches a capacitive touch, what do you expect the action to do? Maybe it will wake up the screen or turn on the LED, and then tell the microcontroller to perform an operation. This operation requires that all of your components have the correct voltage, the capacitive touch sensor and LED are installed correctly, and the microcontroller has been programmed and functioning as expected. This plan for functional testing will guide the quality of the entire PCBA circuit board processing to have a major guarantee.
2. Test Points
The test points are just PCB pads on the board, which are designed for easy detection. For various reasons, you don’t want to rely on probing the pins or pads of the component. The size of these pads is not specified, but they should be large enough to make easy contact with the test probes.
3. In-system Programming
If you look at the internal structure of any product that is complex enough, you may find a programming connector or an empty position on the PCB where the programming connector may be placed. This connector is usually used to program a microcontroller that has been installed on the PCB, so it is called “in-system”. In mass production scenarios, it is meaningless to install this header. It is used by designers for debugging purposes and is not installed in the production process to eliminate costs.
4. Test Fixture
For early prototypes or small-scale designs, you can manually test each board yourself. You will thank your future self for completing this exercise, because it allows you to appreciate and understand what it takes to confirm that your product is working properly. Humans are generally not good at repeatability, so making a test plan, even with checkboxes, can help you avoid skipping any steps.
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