Tom
10-29-2002, 01:53 PM
IPC Advanced Study Guide Page Reference: Page 71, Section 1.9
Understanding the product life cycle is also important. The life cycle begins at the component level. This includes the printed board and continues through the assembly level. The life cycle includes exposure to the manufacturing environments which consists of assembly processes, testing, storage, transportation, and operations.
In determining the requirements for highly accelerated stress testing, one need only look at the environments in which the equipment must operate. This consists of consideration for many factors which deal with the life environment of the equipment in the field. Customer expectations and the items of environment must all be considered when defining the following conditions:
- Temperature range
- Time and temperature
- Temperature rate of change
- Kind and number of temperature cycles
- Duty cycle
- Humidity (moisture) exposure atmospheric pressure condition (earth, space, both) vibration and shock
- ESD, EOS, EMC, EMI and high voltage exposures and requirements
- Chemical exposures, (flux, solvents, salts spray, de-contamination, etc.)
- Radiation (ionizing, light, UV)
- Contamination (dust, oil, paper)
- Pressure conditions
The order of implementing test procedures normally start with electrical continuity. Electrical continuity is performed on the bare board by the board manufacturer. Continuity sometimes includes insulation resistance and dielectric withstanding voltage. These secondary tests are performed to verify contamination on the board or within the inner layers that might impact the insulation resistance or the dielectric separation between circuits that must carry high voltages. Some suppliers also perform controlled-impedance test, to prove that the structure of the board meets the customer's expectations.
At assembly is when testing and evaluation of the product’s performance, over long periods of time, comes into play. At the lowest level, the printed board assembly is evaluated for its continuity through the exercising of individual components. This technique is known as "in-circuit test" and is primarily dedicated towards evaluating component failure mechanisms, opens in the interconnection between the component leads and circuit board, or shorts caused by contamination or solder bridging. Therefore, in-circuit testing is used to find manufacturing defects in the printed board assembly.
In-circuit testers access the board under test through the use of bed-of-nails test fixtures. These fixtures contain pins that make contact with at least one point on every net of the assembly. In-circuit testing places less restrictions on the design, however, requires additional real estate. An attempt should be made to have all the test probes contact the board from one side. This is done since two-sided testing increases the cost of the fixture. One of the primary concerns for in-circuit-tests are that the lands or pins should be on grids; a grid which is compatible which the bed of nails fixtures.
Understanding the product life cycle is also important. The life cycle begins at the component level. This includes the printed board and continues through the assembly level. The life cycle includes exposure to the manufacturing environments which consists of assembly processes, testing, storage, transportation, and operations.
In determining the requirements for highly accelerated stress testing, one need only look at the environments in which the equipment must operate. This consists of consideration for many factors which deal with the life environment of the equipment in the field. Customer expectations and the items of environment must all be considered when defining the following conditions:
- Temperature range
- Time and temperature
- Temperature rate of change
- Kind and number of temperature cycles
- Duty cycle
- Humidity (moisture) exposure atmospheric pressure condition (earth, space, both) vibration and shock
- ESD, EOS, EMC, EMI and high voltage exposures and requirements
- Chemical exposures, (flux, solvents, salts spray, de-contamination, etc.)
- Radiation (ionizing, light, UV)
- Contamination (dust, oil, paper)
- Pressure conditions
The order of implementing test procedures normally start with electrical continuity. Electrical continuity is performed on the bare board by the board manufacturer. Continuity sometimes includes insulation resistance and dielectric withstanding voltage. These secondary tests are performed to verify contamination on the board or within the inner layers that might impact the insulation resistance or the dielectric separation between circuits that must carry high voltages. Some suppliers also perform controlled-impedance test, to prove that the structure of the board meets the customer's expectations.
At assembly is when testing and evaluation of the product’s performance, over long periods of time, comes into play. At the lowest level, the printed board assembly is evaluated for its continuity through the exercising of individual components. This technique is known as "in-circuit test" and is primarily dedicated towards evaluating component failure mechanisms, opens in the interconnection between the component leads and circuit board, or shorts caused by contamination or solder bridging. Therefore, in-circuit testing is used to find manufacturing defects in the printed board assembly.
In-circuit testers access the board under test through the use of bed-of-nails test fixtures. These fixtures contain pins that make contact with at least one point on every net of the assembly. In-circuit testing places less restrictions on the design, however, requires additional real estate. An attempt should be made to have all the test probes contact the board from one side. This is done since two-sided testing increases the cost of the fixture. One of the primary concerns for in-circuit-tests are that the lands or pins should be on grids; a grid which is compatible which the bed of nails fixtures.