In electronics manufacturing, solder defects on a printed circuit board (PCB) ma
ID: 3317859 • Letter: I
Question
In electronics manufacturing, solder defects on a printed circuit board (PCB) may result from the combination of several specifications of design parameters such as a component pad size, drill hole size, fabrication quality of plated metal surface, and the material and process parameters of the soldering equipment. Assuming a 100 PPM solder process (1 solder defect in 10, 000 terminations or joints),
a) Calculate Cpk (assuming a two-sided specification).
b) If the solder equipment is a wire bond machine for which it could be assumed that the defects occur due to one side of the specification limits of minimum pull strength. Calculate Cpk in this case.
c) Assuming you are in a quality team that has to report on their progress toward six sigma using 100 PPM current defect rate, calculate the design specifications expressed in number of sigma for two-sided specifications (in the classical six sigma definition)
d) Re-do part c) for one sided-specification.
Explanation / Answer
Solution:
a.
1. 100 PPM defects (assuming a one-sided specification) is 100 PPM per one tail of the normal cxirve
2. 100 PPM is f(z) = 0.0001 or 2 = 3.72, from standard normal curve tables
3. Implied Cpk =z/3 = 1.24, which is lower quality than two-sided defects
b For two-sided specifications, f{z) = 0.00005 or z = 3.89. If a shift of 1.5is assumedthen all of the failures result from one side of the distribution, whereas the other side is much lower in defects, and therefore contributes no defects. The design is 3.89 + 1.5 = 5.39 or 5.39in the classical six sigma definition.
c. For one-sided specifications, f(z) = 0.0001 or z = 3.72. If we assume a shift of ±1.5 then the design is 3.72+ 1.5= 5.22or 5.22 in the classical six sigma definition.