Production Test Effectiveness of Combined Automated Inspection and ICT Strategies Amit Verma and Charles Robinson Steve Butkovich 1
Automated Inspection Systems and In-Circuit Test • What Place do they have in the process? • What limitations exist? • Use Models for Automated Inspection 2
Confusion of Terms • test – verb (t) A procedure for critical evaluation; a means of determining the presence, quality, or truth of something; a trial • inspect – verb (t) To look carefully at or over; view closely and critically: to inspect every part. 3
Automated Inspection • More Closely Related to the Assembly Process than the test process 4
Automated Inspection Systems • An Important Part of Test Strategy – Premise – Much more effective than human inspection models * 80% Effective * What About Those hidden Joints? – Test Access is Going Away 5
Inspection Standards • Human Operator Standards – JEDEC 001 – IPC 610 6
Inspection Standards • Automated Inspection – Establish a Median Value from a “Known Good Board” – Arbitrary Variation depends on programmer – Inspection methods and limits are inscrutable • IPC 7-32 Committee – Establish Parameters Based on IPC Standards when available 7
Technological Limitations • Analytical Capability – Verifiable Results – Fooled Easily – High False Failure / True Failure Ratio • Image Capability – Lack of Repeatability – BGA Opens 8
Defects vs. Process Indicators • 907 Total Indications • All are Defects that AXI ICT must be Repaired 550 335 ? Insufficient solder ? Excessive solder ? Voids 22 ? Missing bypass caps Functional Test ? Misalignment 9
Does Rework Mean Quality? • Rework Reduces Product Quality – Scrap a PCA before reworking the 4 th time – Particularly for BGA Packages 10 10 10
DEFECT • “A non-conformance that can cause a measurable failure during the product life that must be repaired prior to shipment.” 11 11 11
PROCESS INDICATOR • “An undesirable outcome of the manufacturing process that should be minimized by taking corrective actions on the manufacturing floor using continuous improvement methods, but does not require repair prior to shipment.” 12 12 12
Is Your Defect My Process Indicator? • Class 1 – General Electronic Products – Computers, Consumer Products • Class 2 – Dedicated Service Electronic Products – Communication Equipment, Business Equipment • Class 3 – High Performance Electronic Products – Medical, Avionics 13 13 13
Usage Models AXI AOI ICT OPT Functional Test Screen Functional Reflow Placement Print Solder Test SPEED CLEARANCE RESOLUTION 14 14 14
Statistical Sampling • For Slow Inspection Methods Use the Inspection Systems to Maintain the Assembly Process No. of consecutive assemblies to be inspected n values for 95% confidence Joints inspected per level assembly Percent Fraction DPMO 0.0001 0.001 0.01 5000 10000 15000 20000 Defective defective: p 100 0.01000% 0.0001 39996 400 4 8 4 3 2 200 0.02000% 0.0002 79984 16 8 6 4 300 0.03000% 0.0003 119964 24 12 8 6 500 0.05000% 0.0005 199900 1999 20 40 20 14 10 1000 0.10000% 0.001 399600 3996 40 80 40 27 20 10000 1.00000% 0.01 3960000 39600 396 100000 10.00000% 0.1 36000000 360000 3600 500000 50.00000% 0.5 100000000 1000000 10000 600000 60.00000% 0.6 96000000 960000 9600 1000000 100.00000% 1 0 0 0 15 15 15
Production Test Effectiveness • Defect Coverage with Constrained Resources PTE = (% Total Defects Found) X (Relative Throughput) Test Effectiveness TE = (% Total Defects Found) 16 16 16
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