Design for Testing Handbook
The DFT Handbook will help you understand the importance of PCB testing, various inspection methods, and which one to choose to procure a flawless board.
Sierra Circuits’ Design for Testing Handbook will help you understand the importance of PCB testing, various inspection methods, and which one to choose to procure a flawless board.
PCB design optimization and manufacturing entail substantial efforts and time. Hence, it is vital to inspect the functionality of the entire board. DFT engineers establish a set of testing methods to detect any inaccuracy in the design.
Board testing enables you to identify insufficient component clearance, open or short connections, inaccurate surface-mount pad size, misalignment, and absence of components.
Earlier, the board had enough room to place test points when the number of components was hardly around 100 to 200. Now, a design includes thousands of components and solder connections, especially in HDI boards. The space constraint becomes a concerning issue in deciding proper test positions on a dense board. If any component or connector hampers the design, it would be a nightmare for fabricators and designers. This Design for Testing Handbook certainly helps you position the test points accurately.
Different PCB testing methods
A variety of inspection methods are available in the industry. But choosing the right one can mitigate the risk of potential manufacturing errors.
Manual or visual testing is the simple one that uses a magnifier to check for missing components, contaminated solder paste, solder joint reflow, and warpage issues. The burn-in technique is an efficient way to detect the maximum operational rating of the board. Whereas, functional testing incorporates simple switch-on/ switch-off tests and precise protocols for quality control.
AOI uses high-quality cameras to verify the schematics. You can check different surface feature defects such as scratches, and open and short circuits by implementing this method. It also scans for missing, incorrect, and wrongly placed components. Often, this technique is merged with another type of testing method to ensure authentic results.
X-ray transmission is incorporated for AXI (automated x-ray inspection). This generates clear images of component solder joints. There is also a 3D X-ray inspection method available to scan the semiconductor packages, BGA, and PTH solder joints.
PCB e-test examines the electrical conductivity of the circuit board with respect to the netlist file obtained from the schematic. E-tests can be carried out using two methods: flying probes and bed-of-nails.
FPT includes test points on passive components, untented vias, or terminating end of the components. This method is efficient to detect the value of non-powered elements, open or short circuits, and check the placement of diodes.
ICT technique involves pre-fixed electrical probes aligned under the board through the preset access points. The testing fixtures are used to hold the board in the correct direction. The test jigs check the nets and the values of the components. The flying probe test is the preferred choice over the ICT in recent years because of its less complexity and cost.
Also inside this Design for Testing Handbook
- PCB testing strategies
- Guidelines to design and place a test point for FPT
- Directives to make your board ICT compatible
- Benefits and drawbacks of various testing methods
- Defects that you can identify through board testing
