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The Board Authority

Electrical Test Inspection Issue
(09/2000)

Introduction by Christophe Vaucher

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While PCB selling prices continue to decrease at the rate of six percent per year on average, production yields have become a priority for PCB fabricators who want to remain competitive. Achieving high yields demands a controlled fabrication control. To ensure that one's process is under control requires inspection and test at almost all stages: drilling, imaging, final control, etc. Finally, the feed back loop after inspection and test for process tuning is increasingly important.

In this, the sixth edition of The Board Authority (and second issue dedicated to Electrical Test), we have added a section on inspection, an area growing in importance in the PCB fabrication process. We cover the main fields where inspection and test make sense today:

innerlayer inspection (AOI)
hole / microvia inspection
(final) electrical test
controlled impedance test
stress test

Roadmaps and standardization have not been forgotten. Although new electrical test technologies are not featured in this issue, they have not disappeared from the scene. Rather, these emerging technologies are on their way to market, using "submarine" transportation. But I anticipate good news after the recent conversations I had with several companies developing new processes. As usual, these promising developments in the area of test take more time than initially scheduled.

Inspection and electrical test are evolving processes in the electronics industry. People have realized that these steps, once considered "non-value added processes" actually do have a substantial value in all owing control of the process—leading to higher yields. In other words, for every dollar you may spend on inspection or test equipment, there are many more that you save. The main decision will be to make the right choice when determining the allocation of your investment dollars. Cost modeling is therefore the next step.

The good old days when PCBs were manufactured without inspection are long past.

Because of an increasing number of requirements (higher frequencies, embedded passives, higher densities / finer lines), inspection and test equipment of different kinds will proliferate in the future—specializing on specific requirements, for better performances, better service, and eventually better yields. With all of these benefits, however, electrical test is also generating more confusion. This will be the price to pay for scaling the bleeding edge. It is our hope that focused technical publications, such as The Board Authority, will contribute to a better understanding of these ever-evolving processes. Read on to learn of the present and future requirements of electrical test.

CHRISTOPHER VAUCHER

Electrical Test Inspection
Table of Contents

12	The Role of Inspection in Chip Carrier Manufacturing by DANIEL HERMAN This article covers AOI, LVI, and AVI inspection within the chip carrier manufacturing process.
16	AOI Solutions—Which One is Right for You? by ALEX NATANZON and AMIR GILEAD There are many variables that influence the selection of the ideal system for your AOI needs. This article, together with the model presented, aids in the selection process of an AOI system.
17	Combining Automatic Optical Inspection and Electrical Test—a solution to be considered by RICHARD FRISK Richard Frisk explains how this process combines the best from both the inspection and test processes to give unbeatable fault finding performance on printed circuit boards.
22	Automatically Inspecting Microvias by MARK OWEN An examination of the results of a new inline AOI technology that allows the inspection of 15:1 aspect ratio through holes and blind holes as small as 100 microns (4 mils) diameter, at speeds faster than several multi-headed drills or laser drilling machines.
28	PWB Electrical Test Criteria Roadmap by SUBAHU DESAI AND ITRI—ELECTRICAL TEST PROJECT TEAM This article establishes an industry-wide set of criteria for equipment developers and users to use when determining the needs of a future piece of equipment.
32	The Increasing Density and Decreasing Spacing Between Test Points in PCBs by ENRICO RIGO Better fixture software, improved test equipment, and an integrated test floor approach may be the only way to accomplish a broad range of electrical test on one test floor.
40	Combinational Test: Reducing the Cost of High Density Electrical Test by THOMAS L. GUTHRIE This article reviews the strengths and shortcomings of three families of bare board electrical test hardware, and the effects of these traits on cost per point tested. It also describes how the combinational test technique, supplied by a number of CAM vendors, can optimize the utilization of electrical test hardware.
46	Electrical Test Outsourcing: Partnership to a Total Solution by DAVE ADAMCZYCK Is outsourcing an answer to your electrical test requirements?
49	Testing Embedded Passives by JOSEPH A. CONTI Testing embedded passives has been with us for many years. The use of them is just expanding. It's the same book—just a different cover.
53	The Continued Evolution of Test Data Transfer Format IPC-D-356 by DUANE DELFOSSE This article describes a bit of the history of IPC-D-356, some of the areas where the standard is likely to change, and the progress of the effort underway to update the standard.
56	Controlled Impedance Test by MARTYN GAUDION To ensure signal integrity in production, your designs must be carefully realized by your PCB fabricator.
61	A Test Methodology for HDI Microvia and Traditional PWB Structures by BILL BIRCH IST can provide information that will assist the designer in the selection of design rules commensurate with manufacturing capability and assembly restrictions or methods.