There are various testing methods that can be applied on printed circuit boards. Some of these methods require the application of power, while others are better conducted when power is switched off.
In order to ensure that your printed circuit boards are free of any misplaced or incorrectly placed and spaced components, thorough testing must be conducted on a finished PCB. These tests will also help you detect any component placement that could cause a short in your fully populated circuit board. Additionally, PCBs may be designed with supplementary pads isolated with resistors in order to facilitate the testing procedures.
When power is applied to the printed circuit board, a functional test can then be administered. This testing method is used to simply check if your PCB is capable of doing what it is designed to do. Another power-on test is the in-circuit test. The minor role of this test is to allow you to take physical measurements of voltage, etc. However, its main purpose is actually to enable you to program stable memory systems on your circuit board as well as put into effect the boundary scan test features of some of your PCBs components.
The goal of boundary scan testing is to ensure that the integrated circuits are all mounted correctly on the board. In order to accomplish this, boundary scan testing requires the use of a standard configuration under which all integrated circuits must be tested. The most commonly used standard is the one set by the Joint Test Action Group. The JTAG standard provides the option to troubleshoot interconnections between integrated circuits without using additional physical test probes on the circuit board. When printed circuit boards are unable to meet the JTAG standards, you must then desolder and replace the subpar components.
On the other hand, when the power is switched off, one such testing method that can be conducted for circuit boards is a simple visual inspection or automated optical inspection. Another is analog signature analysis power-off testing. Power-off testing methods are often used in cases where the PCB can only be further damaged when power is applied. This type of testing is also particularly useful during instances when there are no graphic representations available to aid in testing circuit boards.
A bare-board test can be applied on unpopulated printed circuit boards. The testing method involves the application of a small voltage to each circuit connection on the board. A computer is used to identify the exact location of each contact point and its attached electrical test unit will verify whether the required voltage appears at the designated contact points. A short circuit occurs when a connection appears on the board as against the appropriate contact points. In contrast, an open circuit is a missing connection between two points.
Another testing method for unpopulated PCBs is known as industrial CT scanning. Similar to the technology found in medical CT scanners, this technique allows you to see the details of soldered paths and connections on the board via 3D image generation.
Undergoing all these testing methods ensures that the printed circuit boards pass the quality control standards as set by the Joint Electron Device Engineering Council or JEDEC. Nevertheless, even when your circuit board passes all these tests, you should still be aware that many PCBs are static sensitive. Improper handling could damage or completely destroy your board’s various components. A single static charge is already capable of changing the characteristics of a PCB. Therefore after all of the procedures you have gone through to ensure that your board is of the best quality, remember to apply proper transport methods when shipping off your circuit board for either manufacturing or selling.