1 / 24

Compensation for Measurement Errors Due to Mechanical Misalignments in PCB Testing

Compensation for Measurement Errors Due to Mechanical Misalignments in PCB Testing. Anura P. Jayasumana , Yashwant K. Malaiya , Xin He, Colorado State University Kenneth P. Parker and Stephen Hird Agilent Technologies.

terris
Download Presentation

Compensation for Measurement Errors Due to Mechanical Misalignments in PCB Testing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Compensation for Measurement Errors Due to Mechanical Misalignments in PCB Testing AnuraP. Jayasumana, YashwantK. Malaiya, Xin He, Colorado State University Kenneth P. Parker and Stephen Hird Agilent Technologies

  2. Identification of outlier boards using Capacitive Lead Frame Testing data • Improve the accuracy of outlier detection by compensating for systematic errors such as mechanical misalignment and fixture-to-fixture variations Objective BTW 2010

  3. Outline • PCA Based Outlier Detection • Test Data for Mechanical Misalignments • PCA Based Compensation • Summary BTW 2010

  4. Capacitive Lead Frame Testing BTW 2010 Ref: Parker & Hird, ITC 2007

  5. Example: Capacitance vs. Pin Number (for a J245) BTW 2010

  6. Principal Component Analysis (PCA) • 1st Principal Component contains largest variance from the data projection • 2nd Principal Component, orthogonal to the 1st one, contains second largest projected variance • Useful for analyzing multi-dimensional interrelated data 1st PC Measurement 2 2nd PC 0 Measurement 1 BTW 2010

  7. PCA for PCB Outlier Detection Singular Value DecompositionMc = USVT where, UmxnA scaled version of PC scores SnxnDiagonal matrix with square roots of Eigen values in descending order VTnxnEigen vectors (PCs). V Transformation Matrix Z = McVMatrix with z-score values of boards Z-scores of a board are linear combination of all corresponding measurements for that board BTW 2010

  8. Test Statistic for Outlier Detection zik : Value of the kth PC for ith board E : a subset of PCs - most significant PCs are used here • Sort the boards with respect to d1 • Plot cumulative distribution function (CDF) of d1 • Outliers clearly identifiable on right side of plot, typically separated from others by a clear margin BTW 2010

  9. PCA Based Outlier Detection • Treats data holistically • Outlier detection as opposed to threshold based detection Board run numbers on CDF plot from left to right: 52,51,50,53,49,32,73,24,48,25,74,72,83,71,57,47,1,42,56,70,6,68,38,37,58,43,59,41,39,55,40,2,23,78,33,35,44,69,79,54,75,36,64,80,76,31,77,65,60,29,81,63,61,62,3,67,66,82,27,45,28,46,26,30,34,12,8,7,10,9,16,11,13,14,15,4,5,17,22,19,18,20,21 ITC 2009

  10. Capacitive Lead Frame Testing Ref: Parker & Hird, ITC 2007 • Capacitance < 100fF (<10fF with opens faults) • Systematic variations, e.g., variations in connector height, co-planarity of ball connections, sense plate, … • Relatively small mechanical variations can lead to larger measurement variability(Ex. 18fF variation across shift test cases vs. stddeviation of <1fF) • Test values and test limits set now may fail if mechanical variations appear later BTW 2010

  11. Mechanical Misalignments BTW 2010

  12. Raw measurements for B1 with one normal and three left tilted sense plates Tilt_0 Tilt_1 Tilt_2 Tilt_3 BTW 2010

  13. Raw measurements with normal and verticalshifted sense plate for board B5 connector J3 Shift_0 Shift_1 Shift_2 Shift_3 BTW 2010

  14. Compensating for Tilt BTW 2010

  15. Raw measurements with normal and verticalshifted sense plate for board B5 connector J3 Shift_0 Shift_1 Shift_2 Shift_3 BTW 2010

  16. Plot of PC values for Shift Data • Note: • PC-1 can be used to identify the amount of shift or tilt in sense plate • Unlike visual inspection, PCA can identify complex but systematic patterns • If the same board is tested in multiple fixtures, it may be possible to identify differences and compensate for them BTW 2010

  17. Adjusted capacitances by setting all but 1st PCequal to 0 for data B1 • PC-1 captures the tilt information as well as other common information BTW 2010

  18. Data set including two synthetic traces, Def_1 and Def_2 simulating open faults on pins 121 and 165 BTW 2010

  19. Adjusted capacitances by setting only 1st PCs to 0 BTW 2010

  20. Data set including two synthetic traces, Def_1 and Def_2 simulating open faults on pins 75 and 165 BTW 2010

  21. Adjusted capacitance by setting all but 1st PC to zero BTW 2010

  22. Adjusted data based on setting only 1st PC to 0 BTW 2010

  23. Summary • A PCA based technique presented for identification and compensation for measurement errors introduced due to sense-plate variations • Method can be used to separate misalignment related information from defect related information in test data • Approach is NOT sensitive to the order of the pins, and thus shows promise for complex but systematic errors introduced by sense plate misalignments • Method applicable to other kinds of test data BTW 2010

  24. Future Work • Overcome variations caused by measurement errors, mechanical and electrical tolerances • Adaptive and learning techniques for detection and diagnosis BTW 2010

More Related