Quality Assurance

Introduction

How do engineers ensure the quality of design is reflected in manufacturing? When making a high volume product with desired closer to 100 % yield rate, testing in different manufacturing stages is required to ensure final product received at each customers hand provides the best open box experience.

Goal

A good engineer needs to understand basic manufacturing processes and work with manufacturer early on to ensure design  come to fruition .

Basic Types of Testing

They are categorized as two types and stages.

In circuit test (ICT)

it is a board level test with fully assembled electronic components after surface mount reflow process where all components are soldered down. it is ICT test fixtures provides test coverage with incredible speed that is needed for a efficient factory (i.e improve unit per hour (UPH) throughput)

Benefits are coverage and speed

Cons: very costly and can't be reused for other products

• Basic test coverage

  • Open/short test

    • trace are not accidentally shorted due to manufacture imperfections

    • imperfect PCB are thrown out after this test

  • Component values

    • all the passives, resistance, inductor, and capacitor, are correctly populated on the PCB board.

  • Polarity of Analog components

    • diodes are not inverse are not inversely populated

    • electrolytic capacitor are not inversely populated

  • Missing components

Advanced test coverage

For embedded system, often one needs to verify the digital system, and mix-signal circuits. 

Note: This test is commonly seen in the factory test flow, where each board must be verified before inserted in it's mechanical housing.

• • Check main power rails are booted to the right level

  • Check if processor is out of reset and can be flashed with test image.

  • check booting process

  • check memory size and read and write functionalities

  • check boot and idle current

  • check audio driver

  • Check main power rails are booted to the right level

  • Check all I/O ports are functioning (i.e USB can be enumerated, display output is detected and link can be established)

  • Check wireless connectivity chips are functioning

Test fixture

A clamp shell device with embedded spring loaded pogo pins that comes into contact with test points on each board are used.

• One would expect to use this for mass production stage where there is a lot of volume. Speed is key for production lines.

Flying probe test is a fixtureless machine that use use a robotic arm to move from test points to test points.

• One would expect to use this in proto-typing assembly house where investing a dedicated test fixture is too costly.

Functional circuit test (FCT)

It is a test that verify all subsystems are functioning correctly in a final assembled product.

benefits: functional verification after mechanical assembly to verify the final product are working as expected

Con: very manual.

System Image

• verify that correct version of images are loaded on the final product

Secure key provisioning

• Verify secure keys are correctly provisioned in the device (e.g. Digital right management keys (DRMs) for TVs or secure elements for NFC payment transactions)

Screen panel  test

• • Check if screen is damaged

  • check is screen can display correct color spectrum

Speaker quality test

• • check is speaker is assembled correctly to the housing

  • check if frequency response or distortion is within specification

Microphone quality test

• • check microphone is well-sealed

  • check microphone is not damaged and has a high noise

  • check frequency response is within spec

• Any sensor calibration tests

  • calibrate out any part of part tolerance of sensors parameters

wireless connectivity test

• check antenna are not damaged during assembly

• check WLAN chip can be connected to external access points

• check Bluetooth chip can be paired with an external device.

Q&A

Do we need to test every board?

Certain tests are done for everyone such as short and open test but components values test can be done in batches due to using the same rolls or material per each SMT pick and place machine cycle.

Summary & Conclusion

• ICT and FCT are two main test categories ensure quality of manufacturing

• Test coverage for ICT is mainly at PCB board stage

• Test coverage for FCT is mainly at final assembly stage

ICT and FCT are the basic fundamental into quality assure test for device manufacturing.  All those terms might be referred differently in different companies but the main idea is the same. One needs to ensure electronics are done correctly at PCB manufacture, surface mount process (Pick & Place, and Solder reflow), and final assembly stage.