Purpose of Process Controls

Every PCB Assembly manufacturing process has a failure rate and a cost of quality.  There is a trade-off between “perfect” and “low cost.”  For example, a Military or Medical product may have an extremely high quality expectation resulting in a higher price.  The higher price is due to extra prevention and detection processes required to produce the desired quality level.  Conversely, a disposable consumer product may have a lower quality expectation and a lower price due to the removal of processes.  The balance between quality and cost must be discussed between the manufacturer and the customer to make sure that overall expectation of the deliverables is achieved.

An obvious example of the balance between cost and quality occurs in regard to product testing.  Does the product require an In-Circuit (ICT) Test fixture to improve the quality of the deliverable?  The tooling has a cost and needs to be justified.  Some points of discussion are as follows:

  • How much will the quality improve with ICT?
  • Will a Functional Test alone achieve our quality goals?
  • Can AOI at the end of the SMT line eliminate the need for testing?

Although product testing is important because it establishes a baseline quality expectation for the product shipped, it does not capture all the costs of quality.  It is simply a product screen or filter.  How many units did it take to produce a good one?  The common phrase, “You cannot test in quality” speaks to this point.  The true cost of quality lies in the balance between the cost of preventing errors and the cost of detecting them.  Inspection, AOI, ICT and Functional Testing are all methods for detecting defects.  Process controls provide a means to prevent defects.  In general, prevention is more cost effective than detection.  Process controls reduce scrap, rework and price as well as increase on-time delivery.  Having well established, tightly adhered to process controls is integral to a successful manufacturing program.  The appropriate controls for a process depend on the expected results. Some of the common terms and tools are as follows:

  • Visual Aids – intended to aid a human with setup or assembly
  • Detailed Manufacturing Instructions – remove “tribal” knowledge for repeatability and cross training
  • First Article Inspection – ensures the input to the process is good
  • Failure Modes Effects Analysis – a formal process to evaluate:
  1. What can fail?
  2. What makes it fail?
  3. How likely is it to fail?
  4. What are the effects of the failure?
  • Production Part Approval Process (PPAP)
  • Statistical Data Analysis Calculations

MTI utilizes exceptional Process Controls for the prevention of defects and process improvement as well as AOI, human inspection, ICT and functional testing for the detection of defects for all PCB Assemblies.  Our customer specific balance between prevention and detection methods combined with our commitment to process improvement lead directly to:  Higher quality, reduced waste, reduced lead times, and lower total cost.

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