Final electrical test refers to testing that confirms whether a packaged, completed chip operates as specified.

What is evaluated here is:

・Whether functions work

・Whether standard performance is met

・Whether it operates stably over long periods

In other words, it is the final judgment process for whether a product can be shipped to customers.

The reason is clear.

In the packaging process, many elements that affect electrical characteristics are added, such as:

・Solder bonding

・Wire connections

・RDL formation

・Mold encapsulation

Typical examples:

・Connection failures (disconnections / short circuits)

・Increased contact resistance

・Characteristic variation due to thermal strain

・Package-induced leakage

There are many cases where a chip is normal at the wafer stage but becomes defective after packaging.

Final electrical test comprehensively evaluates functions and performance.

Typical examples:

・DC characteristics (current and voltage)

・AC characteristics (operating frequency)

・Power consumption

・Input/output operation

・Timing characteristics

Particularly for logic devices, operating speed and stability are key indicators.

Burn-in testing is performed together with final test.

It is a test in which devices are operated

・At high temperature

・While powered

・For long periods

to force early failures to surface.

Its purposes are:

・Removing early-failure products

・Preventing field failures before they occur

It is essential, particularly for automotive and server applications.

Final test is performed with automated test equipment called ATE (Automated Test Equipment).

Roles:

・Applying high-speed signals

・Measuring voltage and current

・Evaluating frequency characteristics

・Functional testing

For leading-edge logic,

・Simultaneous measurement of thousands of pins

・Evaluation of GHz-band signals

are required, and ATE itself has become extremely expensive equipment.

This is where the difficulty of final test lies.

・Increase the number of test items → quality improves

・However → test time increases

・Result → higher costs

For this reason, designing how much to measure (test coverage design) is extremely important.

Insufficient testing → defects escape

Excessive testing → profitability deteriorates

This is also a strategic decision for the factory.

The more advanced the chip, the more difficult testing becomes.

Reasons:

・More pins (thousands of I/Os)

・Higher speeds (GHz band)

・Increased power consumption

・Increased heat generation

For AI chips and GPUs, there is also the new challenge of thermal runaway during testing.

For this reason, measures such as:

・ATE with thermal control

・Power-limited testing

・Parallel test optimization

are being introduced.

・Final electrical test is the final judgment on whether to ship

・It detects defects caused by packaging processes

・It comprehensively evaluates function, performance, and stability

・Burn-in removes early failures

・Designing test time and cost is important

1.Why is final test necessary even if the wafer test is passed?

2.What is the purpose of burn-in testing?

3.Name one reason why ATE is becoming more expensive.

4.What problems arise if test time is extended too much?

 

Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)

After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.

 

This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.