Tom
11-03-2002, 11:41 AM
IPC Advanced Study Guide Page Reference: Page 43, Section 1.6
Testing of the electronic assembly consists of several basic test conditions. As the assemblies become more complex, the verification processes also become more intense and branch off into additional tests above and beyond the electrical characterizations. Many EMS companies have found that their customer base wants assurances that rely on in-circuit test, automatic optical inspection, and laser analysis where the solder joints are evaluated for opens, shorts, or voids.
Nevertheless, some characteristics are easily identified using different tools, thus any assembly test implementation strategy is usually a combination of verification sequences as well as establishing if a stress conditioning needs to be performed, both before and after the tests are to be executed.
It is important to develop a test philosophy before any design starts. This philosophy is based on the maturity of the product being built, the defect rate that is tolerable during the manufacturing process, the diagnostic capability, the real estate impact, the cost of implementing or not implementing a testing sequence, and most important the customer's perception as to what characteristics on which they require assurances.
If the defect rate is high on a new product, most boards will require diagnostics and therefore the economies of automatic test equipment will demand using all elements of testing and inspection. Electrical testing will verify that parts are connected properly without shorts or opens, automatic optical inspection will verify that the right part is assembled in the proper location and that it is properly oriented, and x-ray will determine solder joint characteristics especially for those components where one cannot see the solder joint, such as the ball grid array.
Testing of the electronic assembly consists of several basic test conditions. As the assemblies become more complex, the verification processes also become more intense and branch off into additional tests above and beyond the electrical characterizations. Many EMS companies have found that their customer base wants assurances that rely on in-circuit test, automatic optical inspection, and laser analysis where the solder joints are evaluated for opens, shorts, or voids.
Nevertheless, some characteristics are easily identified using different tools, thus any assembly test implementation strategy is usually a combination of verification sequences as well as establishing if a stress conditioning needs to be performed, both before and after the tests are to be executed.
It is important to develop a test philosophy before any design starts. This philosophy is based on the maturity of the product being built, the defect rate that is tolerable during the manufacturing process, the diagnostic capability, the real estate impact, the cost of implementing or not implementing a testing sequence, and most important the customer's perception as to what characteristics on which they require assurances.
If the defect rate is high on a new product, most boards will require diagnostics and therefore the economies of automatic test equipment will demand using all elements of testing and inspection. Electrical testing will verify that parts are connected properly without shorts or opens, automatic optical inspection will verify that the right part is assembled in the proper location and that it is properly oriented, and x-ray will determine solder joint characteristics especially for those components where one cannot see the solder joint, such as the ball grid array.