How to Choose a Contract Manufacturer for PTH Assembly

Choosing a supplier for outsourced PTH (Through-Hole Technology) assembly is not a trivial decision.
The wrong choice can lead to delays, rework, hidden costs, and issues that only surface once production is already underway.

In PTH assembly, more than the technology itself, what really makes the difference is method, experience and process control.
In this article, we look at what truly matters when comparing suppliers for through-hole assembly.

Why choosing the right PTH supplier is critical

PTH assembly is commonly used in industrial applications for:

• power components
• connectors and mechanical interfaces
• transformers and relays
• boards exposed to vibration or harsh environmental conditions

An unsuitable PTH supplier may deliver boards that appear to work initially, but fail to perform reliably over time.

1. Specific experience in PTH assembly

(In other words: “we also do PTH” is not enough)

What to ask

• How long have you been assembling PTH boards?
• What types of PTH components do you routinely handle?
• Is PTH a core competence or a secondary activity?

Why it matters

Many EMS providers originate from SMT and treat PTH as a side service.
In reality, PTH requires:

• controlled manual skills
• strong mechanical awareness
• experience with soldering and mechanical fixing

👉 A truly competent PTH supplier does not improvise.

2. Process management (before production even starts)

What to ask

• Do you review the BOM and documentation before starting?
• Do you flag manufacturability issues in advance?
• How do you manage revisions and variants?

Why it matters

Most problems arise before assembly, not during it.
A good PTH supplier:

• aligns documentation
• clarifies critical points
• prevents surprises once production has begun

3. Soldering quality and in-process inspections

What to ask

• What inspections do you perform on PTH solder joints?
• Are there structured visual checks?
• Are inspections carried out only at the end, or during the process?

Why it matters

In PTH assembly, discovering defects late means:

• complex rework
• longer lead times
• higher risk of component damage

👉 In-process inspections dramatically reduce issues.
If you wish, you can explore this topic further in our article on common PTH assembly issues and how to prevent them.

4. Ability to handle small batches, pre-series and variants

What to ask

• Do you accept small batch sizes?
• Do you have experience with pre-series and frequent variants?
• How do you track revisions?

Why it matters

Many PTH projects do not start with large-scale production.
A supplier suitable for SMEs must be able to manage:

• prototypes
• pre-series builds
• small and medium batches

With structure and discipline, not in an ad-hoc way.

Looking to outsource the PTH assembly of your boards?
Request a quotation.

5. Direct technical communication

What to ask

• Will I speak with a technician or only with sales?
• Can I discuss assembly choices directly?
• How are open questions handled during production?

Why it matters

In PTH assembly, technical communication prevents errors.
A competent technical contact:

• clarifies doubts
• proposes solutions
• anticipates problems

👉 This saves both time and money.

6. In-house production vs subcontracting

What to ask

• Is PTH assembly performed in-house?
• Are any phases subcontracted?
• Who is ultimately responsible for final quality?

Why it matters

In-house production allows for:

• greater control
• fewer handovers
• clear responsibility

In PTH assembly, every extra step introduces additional risk.

7. Transparency on lead times, costs and limitations

What to ask

• Is the quotation detailed?
• Are lead times realistic?
• Are constraints and risks clearly stated?

Why it matters

A good PTH supplier does not promise the impossible.
Instead, they prefer to:

• be clear from the outset
• explain trade-offs
• avoid unpleasant surprises

PTH and SMT: why they are not interchangeable

A common mistake is to evaluate a PTH supplier using the same criteria as SMT.
In reality:

• PTH is more manual
• more mechanically driven
• far more dependent on experience

👉 This is why supplier selection matters even more for PTH.

For a complete overview of the service, you can consult our dedicated page on outsourced THT/PTH assembly.

How to tell if a PTH supplier is right for you

In summary, a good PTH assembly partner:

• truly understands through-hole technology
• works with a structured process
• communicates clearly and technically
• manages small batches and variants effectively
• prioritises quality over speed

If you are comparing multiple suppliers, these questions will help you make an informed decision.

Are you evaluating a supplier for PTH assembly?

If you have a PTH production run planned or already in progress, the best way to assess suitability is to discuss it before production starts.

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

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