To ensure optimal quality, a system must go through a myriad of tests to identify areas which need improvement. These tests are extremely important and they should not, under any condition, be neglected. These tests include both bare-board PCB tests and tests after the components are completely assembled.
This is because the presence of shorts or bad solder joints can jeopardize the PCB and these defects can prove consequential. Hence, it is important that we properly establish what PCB jig tests are and the different important tests.
What is PCB Test Jigs?
PCB test jigs are customized devices used to test a PCB. A test jig facilitates the probe of defined test points to help determine the expected inputs and outputs of the PCB. A test fixture, on the other hand, secures the PCB in a firm grip for the execution of the probe. They’re customized in accordance with the board’s application.
Moving on from this, what are the different tests which are often carried out? How important are they?
The 6 Most Important PCB Tests
a. Bare-Board Tests
These are tests carried out on boards to determine the board’s level of conformity to the appropriate circuit connection. It is usually done when there’s no component on it. Bare-board tests primarily comprise capacitance and resistance tests.
Capacitance testing for a bare board revolves around the probe for opens and shorts and this entails charging a net to determine the measure of induced capacity in each net. But due to the variability of the fabrication of circuit boards, this test might have varying degrees of accuracy.
Resistance tests are carried out to determine the level of resistance in each net. The resistance between test points is also tested to determine if it meets the specified limit of resistance or maximum continuity resistance. These tests are carried out in procedures known as continuity tests, short tests, and open tests.
b. Adjacency Test
This test determines the degree of isolation between conductors. It is also another aspect of the protocols of short tests. It entails the use of programs created by software for verifying the conformity of nets to the applicable tolerance level. This can be carried out in two methods: Proximity Adjacency and Line of Site Adjacency.
c. Assembly Level Tests
These include tests executed on a PCB with completely assembled components. The tests can be done via manual inspection or with the aid of Automatic Test Equipment (ATE). ATE is a more expensive alternative that facilitates swifter and more accurate execution of PCB tests. However, they must be selected in accordance with the application of the board to be tested in order to achieve optimal results.
The alternating current passing through a circuit board is influenced in various ways by the circuit’s design as well as the frequency of the current flowing through the circuit. The circuit board’s impedance accounts for the unfolding dynamics of these electron interactions.
Impedance is also determined by the length, width, height, spacing, and separation of conductors. An impedance control test involves the use of a device known as Time Domain Reflectometer (TDR) to verify the circuit’s conformity to the applicable tolerances.
e. Field Effect and Field Measurement Test
This refers to any variation of a test which entails the use of large nets as antennas for sending specific high-frequency alternating current at specific voltages. These tests help in identifying the nets with similar voltage. This allows them to be re-tested for the verification of the shorts.
f. Function Test
This is the final step in the manufacturing processes for PCB. It determines if the finished PCB meets the stipulated quality standards. It is done before the board is shipped out. This test is designed to verify the degree of defect (or lack of it) of the board before it is deployed.
A common functional test, or “hot mock-up” validates the performance of the board’s functions in simple ways. But the more complex functional tests involve a series of procedures that authenticate all the board’s operations.
The procedures of functional tests are contrived in line with the applicability of the PCB, hence it varies for each board. But generally, functional testers are administered on the PCB through the board’s edge connector or test point. The testers replicate the actual electrical environment wherein the PCB will serve its purpose.
No matter the level of precision and conscientiousness deployed in the fabrication of electronic board, there is no way of completely eliminating bugs and issues without the administration of the aforementioned PCB tests.
To guarantee uttermost precision, these tests are applicable only to specific stages of the fabrication, and they should be carried out with utmost diligence.