Tom
10-29-2002, 01:55 PM
IPC Advanced Study Guide Page Reference: Page 72, Section 1.9
Manufacturing defect analyzers (MDAs) provide a low cost alternative to the traditional in-circuit tester. Like the in-circuit-tester, the MDAs examine the construction of the printed board assembly for defects. It performs a subset of the types of tests, but mainly only tests for shorts, opens and faults without applying power to the printed board assembly. In high volume production with highly controlled manufacturing processes (statistical process control techniques) MDA may be a viable part of the printed board assembly test strategy.
Functional testing is used to test the electrical design functionality. Functional testers access the board under test through the connector. Sometimes bed-of-nails test points are also used. The board is functionally tested by applying pre-determined stimuli at the printed board assembly input while monitoring the printed board assembly’s outputs. This function is performed to ensure that the design responds properly to the intended performance characteristics.
When it comes to highly accelerated stress testing, the exposure conditions are determined based on the environment which the product will operate, and it’s life expectancy. These issues are usually accomplished by testing coupons that are representative of the product being produced. Burn-in conditions are mainly to see that the board operates under the end-user environment and that early failures do not occur. The reliability of components are often referred to as "meeting the conditions of a bathtub curve."
Early failures are in the first hundred hours of component life. Components then survive for many years before failure rates again start to increase. Since this characteristic has been known for many years, companies attempt to exercise the board through its functions (under power), in a higher temperature and humidity than it might normally see in service. The time for burn-in can be as low as 4 hours and as high as 24 hours. Usually companies deliver products that have been burned-in. Burn-in cycle is not intended to degrade the assembly, merely eliminate infant mortality problems.
Highly accelerated stress testing, however, is intended to test the product to failure. In these issues, one takes and evaluates the number of cycles that a product can survive and the manner in which it meets those survival characteristics. When designing a HAST program, one normally attempts to develop a test vehicle where measurement and conditioning of the product can be easily evaluated as the products goes through its HAST cycles.
Manufacturing defect analyzers (MDAs) provide a low cost alternative to the traditional in-circuit tester. Like the in-circuit-tester, the MDAs examine the construction of the printed board assembly for defects. It performs a subset of the types of tests, but mainly only tests for shorts, opens and faults without applying power to the printed board assembly. In high volume production with highly controlled manufacturing processes (statistical process control techniques) MDA may be a viable part of the printed board assembly test strategy.
Functional testing is used to test the electrical design functionality. Functional testers access the board under test through the connector. Sometimes bed-of-nails test points are also used. The board is functionally tested by applying pre-determined stimuli at the printed board assembly input while monitoring the printed board assembly’s outputs. This function is performed to ensure that the design responds properly to the intended performance characteristics.
When it comes to highly accelerated stress testing, the exposure conditions are determined based on the environment which the product will operate, and it’s life expectancy. These issues are usually accomplished by testing coupons that are representative of the product being produced. Burn-in conditions are mainly to see that the board operates under the end-user environment and that early failures do not occur. The reliability of components are often referred to as "meeting the conditions of a bathtub curve."
Early failures are in the first hundred hours of component life. Components then survive for many years before failure rates again start to increase. Since this characteristic has been known for many years, companies attempt to exercise the board through its functions (under power), in a higher temperature and humidity than it might normally see in service. The time for burn-in can be as low as 4 hours and as high as 24 hours. Usually companies deliver products that have been burned-in. Burn-in cycle is not intended to degrade the assembly, merely eliminate infant mortality problems.
Highly accelerated stress testing, however, is intended to test the product to failure. In these issues, one takes and evaluates the number of cycles that a product can survive and the manner in which it meets those survival characteristics. When designing a HAST program, one normally attempts to develop a test vehicle where measurement and conditioning of the product can be easily evaluated as the products goes through its HAST cycles.