PTH Assembly: 7 Common Issues That Cause Delays and Defects

PTH assembly (Through-Hole Technology) remains a cornerstone of industrial electronics. Power components, connectors, transformers, relays and PCBs designed for harsh environments still rely heavily on through-hole mounting.

However, precisely because it is often manual or semi-manual, PTH assembly is also one of the production stages most exposed to process errors, variability and unexpected issues.
Many problems only emerge once production is already underway — or worse, after delivery — leading to delays, rework and additional costs.

In this article, we look at the 7 most common issues in PTH assembly and how to prevent them using a structured, industrial approach.

Why PTH assembly is still critical in production

Unlike SMT, PTH assembly involves:

• components subjected to mechanical stress

• manual operations that require a high level of experience

• solder joints that must ensure long-term mechanical robustness, not just electrical continuity

The issue is not PTH technology itself, but how it is managed.
An improvised PTH assembly may work in the lab, but it does not scale to industrial production.

👉 For a complete overview of the service, see our dedicated page on outsourced THT / PTH assembly.

1. Cold or non-uniform solder joints

What happens

In PTH assembly, solder quality depends heavily on the operator, the sequence of operations and process control. Without a defined method, it is easy to end up with solder joints that are:

• dull in appearance

• not fully wetted

• mechanically weak

Consequences

• intermittent faults

• failures that are difficult to diagnose

• field returns after weeks or months

How to prevent it

• clearly defined soldering procedures

• experienced operators for PTH components

• structured and repeatable visual inspections

In PTH assembly, repeatability matters more than speed.

2. Mechanical stress on component leads

What happens

PTH components such as transformers or connectors may be subjected to stress during:

• insertion

• lead bending

• mechanical fastening

Consequences

• micro-cracks in component leads

• failures under vibration or shock

• issues that only appear in the field

How to prevent it

• correct assembly sequences

• attention to mechanical aspects, not just soldering

• proper support for heavy components

3. Incomplete or misaligned documentation

What happens

Outdated BOMs, unclear revisions or inconsistent files are among the most common root causes of errors.

Consequences

• incorrect component installation

• production stoppages

• avoidable rework

How to prevent it

• initial documentation review

• alignment before starting production

• orderly revision management

One hour spent before production starts can save many more later on.

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4. Underestimating critical components

What happens

In PTH assembly, not all components are equal. Transformers, relays and connectors require specific attention.

Consequences

• incorrect assembly

• testing difficulties

• reliability issues

How to prevent it

• identify critical components at an early stage

• plan dedicated handling during assembly

• adapt inspections and verification steps

5. Uncontrolled manual variability

What happens

Without a defined method, each operator tends to work “their own way”.

Consequences

• inconsistent quality

• difficulty repeating production runs

• issues when moving from pre-series to full production

How to prevent it

• defined work sequences

• clear assembly instructions

• intermediate checks

Manual work is not the problem — the lack of method is.

6. Insufficient checks before final testing

What happens

Defects are only discovered at the very end, when they are most expensive to fix.

Consequences

• extensive rework

• longer lead times

• wasted resources

How to prevent it

• progressive in-process checks

• targeted visual inspections

• catching issues before final test

7. Poor management of variants and pre-series builds

What happens

Hybrid production runs — halfway between prototype and series — without clear differentiation.

Consequences

• operational confusion

• repeated errors

• difficulty standardising processes

How to prevent it

• clearly define what is prototype, pre-series or series

• track variants accurately

• maintain orderly documentation

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How to avoid these issues with an industrial approach

In PTH assembly, experience and process matter more than technology.
Avoiding problems means:

• anticipating critical issues

• working methodically

• communicating clearly and technically

• treating even small batches as real production runs

A good PTH partner does not simply assemble boards — they help you launch production without surprises.

Find out how to choose the best supplier for PTH assembly of your electronic boards.

Are you facing issues with PTH assembly?

If you are experiencing delays, defects or difficulties managing through-hole assembly, the best way to resolve them is to address the topic before production starts.

👉 Talk to a PTH manager
👉 Request a quotation for PTH assembly

Even with preliminary information, we can help you assess risks, lead times and the most suitable approach.