PCBA Manufacturing Test Effectiveness
PCBA manufacturing test effectiveness
The overall effectiveness of PCBA manufacturing test should be compared against the defect universe.
The defect universe for each component in the BOM (Bill of Materials) includes:
Presence (the component is present)
Correctness (it is the correct component)
Orientation (if the component is polarized, it is not rotated by 180 degrees or for a QFP or BGA is not rotated by 90, 180 or 270 degrees)
Live (the component is basically alive – note this is not a full functional qualification)
Alignment (the component is properly centered, free of skews or small rotations)
The defect universe for component pin connections includes:
Shorts (unwanted continuity to other nearby connection points)
Opens (lack of continuity between component and the intended board connection)
Quality (free of malformation, excess or inadequate solder, cold solder voids, etc.)
The first letters of each potential defect forms the acronym PCOLA-SOQ. PCOLA-SOQ represents a more comprehensive indicator of a PCBA manufacturing test effectiveness than the historical test coverage formulas.
PCOLA-SOQ is a more rigorous method of analyzing the completeness of PCBA manufacturing test to detect all the possible faults in the defect universe. It can be used to develop a test strategy using complementary test technologies to encompass a larger portion of the defect universe.
The process of assigning PCOLA-SOQ scores forces us to think in greater detail the effectiveness of a chosen PCBA manufacturing test to cover a defect class. PCOLA-SOQ will guide the PCBA test strategy owner and the test developer to:
Define the defect universe.
Identify coverage gaps within the defect universe.
Selecting and implementing complementary tests to close critical coverage gaps.
Focus efforts to implement quality tests for critical defect classes.
PCOLA-SOQ can be as basic as you want it to be or as detailed and exact if required. A basic PCOLA-SOQ may simply use ‘1’, ‘0.5’ and ‘0’ scores as in the examples above. If a more detailed PCOLA-SOQ is desired, weights can be used to derive a value between 0 and 1 to reflect the capability of the test to detect every possible fault of a component and solder connection within a category.