Quality is the prime requisite for any PCB manufacturing process. This is because the performance of an electronic circuit depends on the PCB. Any failure in PCB components can affect sales, products, and business reputation. Today, PCB manufacturers are taking all efforts to ensure the quality of PCB is maintained throughout the manufacturing and testing and inspection processes. In the previous post, we have seen some of the common PCB challenges. However, here we will discuss the popular types of PCB testing and inspection services provided by PCB assembly and manufacturing services.
Understanding Various Types of PCB Inspection and Testing Services
Following are the 10 important types of PCB inspection and testing conducted by PCB manufacturing services.
- Boundary Scan Testing: This is a common method of testing wire lines, or interconnections on the PCBs without physical access. This testing is standardized as the IEEE Std.1149.1.
- In-Circuit Testing: This testing is conducted to test a populated PCB for resistance, opens, capacitance, and other quantities. This testing is performed with specialized testing equipment bed of nails tester or with a fixtureless in-circuit test set up.
- Flying Probe Test: This is a common testing technique used to verify the integrity of prototypes. The flying probes are connected to a camera and test points for detailed inspection. The flying probes cab access component pins either directly, or through automated test points. This is a simple and straightforward test to debug irregularities.
- Automatic X-Ray Inspection: This test is conducted to inspect hidden components underneath the PCB. The X-rays are used to examine PCBs, specifically the solder joints and components under the chip. The device used for the testing features a tilt function, which allows a tester to use an oblique angle to solder joints, as well as ensure that soldering and paste are not coalesced.
- Automatic Optical Inspection: This refers to automatic visual inspection of a PCB by a camera in the manufacturing phase. The Automatic Optical Inspection (AOI) is conducted to test various features such as component skews, billboarding, area defects, insufficient solder joints, etc. The AOI can be used in Surface Mounted Device (SMD) manufacturing during pre-reflow, post paste, or wave areas.
- Tin Whisker Testing: This test is performed to test tin whiskers on PCBs. Tin is used as a finishing material for various electronic components, which can grow into whiskers. These structures can conduct electricity, which may affect the operation of the device. The tin whiskers can be corrected through conformal coating, or by replacing tin plating with other metals, as well as selecting a low-stress tin finish.
- Optical Microscopy Testing/ Scanning Electron Microscope: This is one of the preferred and popular testing techniques to detect defects, faults, and problems in soldering and assembly. In optical microscopy, a microscope is used to magnify a test sample to see its microstructures. This technique is used in conjunction with micro sectioning to test the accuracy of samples. The SEM machine can be fitted with an energy dispersive X-ray detector, which allows a user to determine elemental sample composition. This helps identify impurities as well as surface contamination, and helps ensure that quality materials are used for manufacturing.
- PCB Contamination Testing: This testing is conducted to avoid ionic contamination. In this method, a PCB sample is immersed into a solvent, which helps dissolve the ionic contamination. The resistance of the solvent changes due to ionic elements. This resistance is measured and plotted on a contamination testing curve. The contamination can be caused by flux residues, or mishandling of PCBs.
- Micro-Sectioning Analysis: This method is also known as metallographic preparation, or cross-sectioning. The micro-sectioning analysis is conducted to investigate opens or shorts, component defects, thermo-mechanical failures, raw material evaluations, solder reflow failures, etc. In this method, the internal structure of a solder joint is deeply analyzed. A 2D slice is removed from a sample, is placed in an epoxy resin, and is allowed to solidify. The solidified component is then receded using abrasives, and exposed. The exposed component is polished, until it becomes reflective. The sample is compared with other non-faulty micro-sectioned components, and examined using optical/electron microscopy equipment.
- Functional Testing: These tests are conducted at the last phase of manufacturing to test if the PCB is functioning as per the requirement. The functional tests are automated and conducted using test software. During functional testing, the tester concentrates on areas such as control hardware, switch matrix, interface/fixture, test and measurement, and power supply, and distribution.
Each of the above- mentioned PCB inspection and testing processes provide benefits to clients as well as manufacturers. You can get in touch with your PCB manufacturer to understand the benefits of each PCB inspection and testing service individually.
