circuit boards tested after assembly
The intricate connection between the components on a circuit board must be solid for it to function properly. This is why careful inspection, solderability tests, and functional testing are all crucial steps in circuit board assembly. These comprehensive tests ensure that the final product will meet and exceed customer expectations.
Component Verification: Before any components are installed, a thorough inventory check must be conducted. This includes confirming that the correct resistors, capacitors, diodes, transistors, and integrated circuit board assembly are available for each board. Identifying these issues prior to assembly can avoid costly errors later on in the process.
Solder Paste Stenciling: The application of precise solder paste stencils is necessary for proper component placement and accurate soldering. These stencils are designed to match each PCB and allow for the deposition of the correct quantity of solder. This step helps ensure that the resulting connections are sturdy and will hold up to mechanical stresses.
How are circuit boards tested after assembly?
Boundary Scan: This method allows the computer to “see” inside the ICs on the board without physical access. It uses a shift register built into each boundary-scan compatible IC chip that allows data to enter and exit it via an interface port called a Test Access Port (TAP). This information is transferred through a 4-wire serial interface that’s encoded in a Boundary Scan Description Language file, which is supplied by the IC manufacturer. This gives the computer an X-Y map of the chip, and each test point. The in-circuit tester then uses a computer program to match the coordinates of these test points with those of your PCB. The computer then transmits test data to the IC, testing its functionality.
In-Circuit Testing (ICT): The in-circuit test is often referred to as the bed of nails because of the way it looks and works. This type of testing pushes power through your electronics, typically to its maximum-specified load capacity. This is a time-consuming and destructive test, but it confirms that your boards are able to withstand the demands of a real-world environment. It’s especially important for equipment that cannot afford failure, like medical or military equipment.
Functionality Testing: This includes evaluating the PCB’s ability to interact with embedded software. It may also examine the PCB’s ability to manage power and assess its energy consumption. This can reveal compatibility issues or performance gaps that can impact the end-user experience.
Other tests include environmental tests and quality assurance checks that can vary widely by PCB and end product. These can include IP rating tests, water resistance tests, voltage surge tests, electromagnetic interference (EMI) tests, and radio-frequency interference (RFI) tests.
If a test fails or the product fails to live up to expectations, a detailed investigation is required to understand what caused it. A few common causes include contamination in the material, improperly plated copper inside through-hole walls, and insufficient wetting of the leads (areas where the molten solder only partially covers the wire). These investigations typically involve microsections to find shorts, defects, openings, and other problems that can cause malfunctioning or even dangerous circuits.
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