Ensure Reliability With PCB Cross-Section Analysis
IPC-TM-650 gives the complete testing manual for PCB boards and specifies how to verify electronic assemblies.
In PCB cross-section analysis, the PCB material is characterized and the failure analysis is conducted.
PCB cross-section analysis can be performed at different stages of the PCB fabrication or on the assembled electronic boards.
PCB cross-section analysis is one method to ensure the reliability and quality of the PCB board under test
Analyzing PCB failures is an essential step for successful PCB design. In PCB failure analysis, problems are identified using a variety of methods. PCB cross-section analysis is one method used to ensure reliability. This type of analysis measures the quality of a PCB board under test. Even though PCB cross-section analysis damages the PCB board under test, it helps engineers ensure future designs avoid the same issues.
A product’s life cycle depends on the reliability of the PCBs it uses. If one PCB fails to operate, the entire product might fail. To compete in the market, it is important to ensure PCBs are failure-free.
There are various testing methods available for analyzing failure in PCBs, including destructive and non-destructive tests. The technical procedures for these tests are devised by the Institute for Interconnecting and Packaging Electronic Circuits (IPC) and issued as a testing manual under the IPC-TM-650 specification. IPC-TM-650 sets a common standard for all PCBs in electronic products to ensure consistent and repeatable performances. IPC-TM-650 gives the complete testing manual for PCB boards. It also specifies how to verify electronic assemblies. The procedures in the testing manual include electrical testing, inspection, environmental testing, etc. IPC-TM-650 also details what equipment to use for testing as well as the procedures to follow.
In section 2.1 of IPC-TM-650, the guidelines for PCB cross-section analysis are described. PCB cross-section analysis evaluates the internal structure as well as the quality of the PCB. A quality check is made based on the thickness and distribution of the coating and metallization as well as the quality of the solder joints and interconnects. With the information gathered from the tests, it is possible to identify any process deviations and ensure boards meet industry standards.
PCB Cross-Section Analysis
In PCB cross-section analysis, the PCB material is characterized and failure analysis is conducted, focusing on any interconnection defects. PCB cross-section analysis is particularly helpful in spotting internal failures in a PCB.
Compared to tests such as visual inspection or X-ray inspection, PCB cross-section analysis is a destructive test. Let’s take a look at the steps involved:
Step 1: Cut and Mount a Section
In PCB cross-section analysis, a section around one square inch in area of the PCB is cut out and mounted into a potting material. The potting material hardens around the PCB cutout and provides support and protection to the sample from the subsequent processes of polishing and etching.
Step 2: Polish or Etch and Optical Microscopy
The sample is polished until the target plane to be examined is reached. The PCB specimen is then examined under an optical microscope. The optical microscope helps show the microstructure of the PCB cross-section. Instead of polishing, the PCB specimen can be etched before viewing it under the optical microscope.
Step 3: Use a Scanning Electron Microscope
The scanning electron microscope helps in examining the PCB specimen surface or the PCB cross-section. For SEM examination, neither polishing nor etching is required before microscopy. Various modes of SEM are used for gathering different information, as given in the table below.
What Can PCB Cross-Section Analysis Identify?
PCB cross-section analysis reveals information unavailable from X-ray inspection or visual inspection, including:
- Solder grain structure
- Cracks or voids
- Composition of tiny inclusions
- Intermetallic boundary conditions between the conductor pad and solder
- Solder build-up
- Through-hole filing
- Wetting conditions
- Ball-grid array solder joints
With PCB cross-section analysis, the root cause of failure can be identified. Since this type of analysis provides information on the thickness and distribution of copper plating and intermetallic boundaries, process checks are also possible.
When to Conduct PCB Cross-Section Analysis
PCB cross-section analysis can be performed at different stages of the PCB fabrication processor on the assembled electronic boards. It is the go-to test for failure analysis of PCBs. PCB reliability can be guaranteed once the specimen passes the PCB cross-section analysis successfully.
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