January 15, 2014

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Complexity of the PCB Assembly and Possible Test Solutions

Introduction

This is to describe the complexity of the PCBs manufactured today, and possible test solutions available for the manufacturer to deliver a defect-free product, and deliver on-time to the market.

Complexity and Challenges

The complexity of the PCB is an increasing trend. Most manufacturers are assembling their boards with high complex devices and with very minimal electrical access to test equipment to make contact to test and certify the working of the board functionality. Most of the manufacturers prefer to have SoC, ASIC, PLD and other high complex devices in their products. The increase in the number of components, and minimum electrical access, means a lower yield as well as being highly difficult to diagnose if any problem occurs in the PCB.

The challenge to the test engineering team is achieving the highest fault coverage with the available testing options within the manufactured and assembled PCB. Every manufacturer prefers to have 100% fault coverage for all of their products delivered. The test engineer should evaluate the possible test opportunities available with the available test equipment. This will ensure cost effectiveness and improved time-to-market for such products.

Types of Test Systems available

There are many types of test systems available in the market today. The manufacturer will triage with the test engineering team to make an investment in buying the required test systems, which will assure the highest fault coverage with less cost. Some of the test systems are:

  • Manufacturing Defect Analyzer (MDA)
  • In-Circuit Tester (ICT)
  • Flying Probe Tester (FBT)
  • Board Functional Tester (FATE)
  • Automatic Optical Inspection System (AOI)  
  • Automatic X-Ray Inspection System (AXI)
  • PXI Test System (PCI eXtensions for instrumentation )

Each of the test systems above has unique features and limitation of their own.  In most cases, manufacturers combine two or more types of test equipment to achieve the highest fault coverage.

Testing Techniques

In this portion, I would like to touch on the different types of testing techniques which are followed to achieve complete fault coverage of the PCB.

  • Contact test
  • Open/short testing
  • Solder joint testing (for BGA and high-complex pin count devices)
  • VI-signature analysis
  • Analog testing (such as resistance, capacitance, inductance, etc.)
  • Learn and compare board characteristics (unpowered method)
  • Component/device functional testing independently (through ATE/ICT Nails)
  • Clip-on testing (using lower-end board testers)
  • Cluster/block testing
  • Boundary scan testing (JTAG)
  • Memory testing (for memory devices)
  • Functional testing of the whole PCB

Based on manufacturer needs, the test engineering will follow the appropriate test techniques in their test programs.

Conclusion

In order to achieve maximum fault coverage for manufactured PCBs, combining different types of test systems with different test techniques are followed in a real scenario. This will allow every manufacturer to deliver defect-free products to the market.

References
1. A Book “Building a Successful Board-Test Strategy” Second edition, 2001 – Author Stephen F. Scheiber 
2. http://www.radio-electronics.com/info/t_and_m/ate/automatic-test-equipment-basics.php