Your Board Already Has a Powerful PCB Test Capability

Simon Payne, CEO, XJTAG | October 6, 2026 Subscribe to LinkedIn newsletter

The design has been verified, production starts, the first boards come through test successfully.

Then one fails.

That is the moment you discover how good your test strategy really is.

Finding a fault on a prototype is one thing. The development team knows the design intimately, has access to schematics, debug software and bench equipment, and may be prepared to spend hours investigating an unusual problem.

Production is different.

When a manufactured board fails, the question isn’t simply:

“Does it work?”

It becomes:

“What’s wrong with this particular board, and how quickly can we find the fault?”

Prototype Debugging and Production Diagnosis Are Different

During development, engineers are often investigating the design itself.

Is the interface configured correctly?

Does the circuit behave as expected?

Are the component values right?

Does the software initialise the hardware correctly?

By the time a product reaches production, the design should already have been proven. The production test is answering a different question:

Has this particular assembly been manufactured correctly?

That changes the nature of the investigation.

A Failure Needs to Narrow the Search

Imagine a board fails because an interface is not responding.

A basic production test may tell you exactly that:

Interface failed.

But the engineer still has to work out why.

Is there an open connection?

A short?

A missing component?

A badly soldered pin beneath a BGA?

An incorrectly fitted device?

Or is the problem somewhere else entirely?

A useful test strategy should progressively reduce that search area.

The closer the test can get from:

“Something is wrong.”

to:

“Start looking here.”

the more useful it becomes.

This Is Where Structural Information Helps

Functional testing is extremely valuable in production because it proves that the completed product behaves as expected.

But when a functional test fails, the symptom can sometimes cover a large area of hardware.

Structural testing provides a different layer of evidence.

Boundary Scan can often verify inaccessible PCB connections independently of the application software and relate unexpected results back to the nets and devices involved.

That can help answer an important question:

Is this an assembly problem, and if so, where should we investigate first?

Boundary Scan does not replace functional production testing.

It complements it by providing another way to understand the hardware beneath the symptom.

One Failed Board May Be Manageable

If one board fails, spending an hour investigating it may not seem significant.

But what happens when ten fail?

Or fifty?

Or when the same type of fault appears repeatedly? At that point, diagnostic time starts affecting manufacturing throughput.

That is why the economics of production test aren’t determined only by how quickly passing boards can be tested.

They are also influenced by how efficiently failed boards can be diagnosed.

A fast PASS/FAIL test followed by hours of fault finding may not be as efficient as it first appears.

Don’t Wait for the First Failure to Think About Diagnosis

There is an important Design for Test lesson here.

When the first failed production board arrives, the PCB design is already complete.

If a reset cannot be controlled, an enable is inaccessible or an important interface cannot be exercised independently, the test engineer has to work within those constraints.

The opportunity to make a simple schematic change may have disappeared months earlier.

This is why testability shouldn’t only ask:

“Can we detect a failure?”

It should also ask:

“If it fails, what information will we have?”

That question is much easier to answer while the schematic is still open.

Carry What You Learned During Bring-Up into Production

There is another opportunity that is often overlooked.

Structural tests developed during prototype bring-up don’t necessarily need to be discarded once the design is working. Tests that proved connectivity, memories, peripherals or interfaces during development may also provide useful coverage in production. That means the effort invested in understanding the first prototypes can potentially become part of the manufacturing test strategy.

Instead of starting again, knowledge moves forward with the product.

Closing Thought

A string of passing boards doesn’t really test your diagnostic strategy.

The first failure does.

That is when you discover whether your test simply detects a problem or actually helps the engineer understand it. And the difference between knowing:

“This board failed.”

and:

“This is where you should start looking.”

can determine whether the problem is diagnosed in minutes, investigated for hours or placed on a growing bone pile marked:

Investigate later.

The best production tests don’t just catch faults.

They help engineers understand them.

Board Design Tip of the Week

Before releasing your next design, choose three realistic manufacturing faults.

For example: