A brief introduction to PCBA functional testing

August 25, 2017 Courage Guo, Seeed Studio Fusion

Functional testing, also known as behavioral testing, runs tests according to the characteristics of the product description, user plan, and operation scheme to make sure the product meets the design requirements in both product description and operation scheme. Functional testing ensures that the program runs properly, tests the software as required by the function, and tests all the features and functions of a system to ensure that it meets the requirements and specifications.

Functional testing is also called black box testing or data driven testing, because only the various functions need to be tested – from the software product interface, architecture of test cases according to the written demand, input data evaluation between expected results and actual results – not the internal structure and code of the software.

PCBA functional test will cover both hardware and software. Normally, the users need to send a test plan to the manufacturer to guide the test engineer. For example, your need to have a list of behavior and results (e.g., if you press button one, the green light turns on). 

1. The current PCBA functional testing is divided into the following:

1.1 Manual test jig

A manual test fixture uses a bake lite and acrylic needle plate to out go the input/output and power supply for PCB, and simulate the input/output manually. The result is confirmed by the tester.

Since the cost of labor is high and efficiency of it is slow, testing by humans has been replaced gradually by manual test jigs, which are low cost because of their higher accuracy and lower requirement for human involvement, though testing is only partial and quality is not guarunteed.

 

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1.2. MCU control function test

Make clamp lock or pneumatic jig and pull out the probe. Then connect the input/output power to the microcontroller circuit so that the microcontroller runs the test program  and measures the analog input/output automatically.

This method is characterized by moderate price, high testing efficiency, guaranteed testing quality, and less human intervention. However, the versatility of this method is lacking, generally only applying to a machine equipped with a fixture.

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1.3. PCBA universal automatic test system

The PCBA universal automated test system is designed for the majority of manual testing. As the testing system is powerful, it can test all kinds of PCBA and become a universal testing system.

Detection principle of humanization: By sampling the parameters of the model, set the error range, compare with the measured plate, and determine whether it is qualified.

The test of simplicity: Manually press the needle bar and the system will be automatically processed. The product quality can be judged by the system, ruling out the effect of human judgment factors. Moreover, its speed is unmatched by manual test.

The system is composed of acquisition, control board, and testing software. It is connected with programmable AC/DC power supply and DC load. The high sampling rate product can be supplied with an external oscillograph.

The system can test the PCBA synchronization signal, user interface, modular programming environment model, and conversion.

This method is more expensive, but the test speed is quick and does not need require human intervention. It is versatile in its applications and offers a more comprehensive test.

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PCBA function test contains:

  • Power supply test: power is working properly; test each point’s voltage
  • Port (Interface) test: whether there is Short or Open, causing in dysfunction
  • Integrated circuit module ICI/O read and write function test: Flash&EEPROM&CPU&SDRAM&Logic, IC, etc.
  • Special function test (different circuit board requirements inconsistent): such as infrared, the need for external receiver.

PCBA testing depends on what test you're doing, ICT or FCT, and different testing methods will make a big difference, because ICT's equipment and tooling are relatively expensive. But ICT can give good test results, which can bring great benefits to PCBA repair.

For better understanding PCBA functional test, view Seeed Fusion’s PCBA test capabilities as a reference. 

Courage Guo is an electrical engineer for Seeed Studio Fusion. He is an electronics design engineer, web developer, robotics enthusiast as well as a geek who loves to do penetration testing and build things.

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