When Does Through-Hole PCB Assembly Make More Sense Than SMT?

Table of Contents

1. Which Design Requirements Favour Through-Hole PCB Assembly?

2. How Should You Choose Between Wave, Selective and Hand Soldering?

3. What Must Be Locked Before You Request PCB Assembly and Soldering Services?

4. How Can a Through Hole PCB Assembly Service Support a Cleaner Release?

5. Conclusion

6. FAQs

The PCB design is very compact. Should we definitely choose SMT? Actually, that's not necessarily the case. In actual production, some components not only need to achieve electrical connections but also have to withstand plugging and unplugging, pulling forces, vibration, and even their own weight. For example, connectors, relays, transformers, and terminal blocks that are frequently plugged and unplugged will bring certain mechanical stress to the solder joints during use.

In such cases, through-hole PCB assembly (THT PCB assembly) is often more suitable than relying solely on surface pads for support. When the component pins pass through the plated through-holes before being soldered, it not only completes the electrical connection but also provides a more stable mechanical retention. Of course, this does not mean that all components with pins are suitable for THT. For small-sized, multi-pin, and densely-arranged components, SMT still has more advantages.

So, the key point is not which one is better between SMT and THT, but what kind of working conditions the components actually have to endure. When pursuing high density, miniaturization, and multi-pin designs, SMT is usually more appropriate; if the connection position needs to withstand large mechanical loads, or the component itself has higher requirements for fixation strength, then through-hole PCB assembly is usually a more suitable choice. In this blog, we will specifically look at which designs are more suitable for THT, how to choose different soldering methods, and what key data and process requirements need to be confirmed before production.

Which Design Requirements Favour Through-Hole PCB Assembly?

The strongest case for through-hole mounting starts with the job of the component. High-force connectors, relays, transformers, switches, terminal blocks and some power parts can benefit when their leads pass through the PCB rather than sit only on surface pads. The engineering review should also consider insertion force, cable pull, vibration, thermal mass, accessible clearance for soldering and whether technicians may need to replace the part later.

How Much Mechanical Load Will Each Connection Carry?

Start with the real load path, not the component category. A light connector inside a protected enclosure may be an SMT candidate, while an external connector on the same board may need plated holes because users will push, pull and twist its cable. Through-hole lead patterns can also provide useful mechanical positioning during insertion. That can make orientation and stand-off control easier when the drawing defines them.

For a through hole PCB assembly service, the useful inputs are specific: component lead diameter, finished-hole requirement, body height, insertion side, polarity mark, keep-outs and any board support or fixture constraint. These details let engineering check whether the hole, land and soldering route work together before materials are committed.

Does the Assembly Need a Mixed-Technology Layout?

Most production boards do not need an all-or-nothing decision. THT PCB assembly can sit beside fine-pitch SMT parts when the design keeps clear process boundaries. For example, a controller may use SMT for logic and memory, then through-hole mounting for field connectors and a transformer. The PCB layout should show which side receives each component, which parts require post-reflow insertion, and whether a wave-solder pallet or selective-solder fixture will protect nearby surface-mount pads.

This is also where PCB assembly and soldering services become more valuable than a simple parts-placement quote. A build review can identify a connector that blocks a solder wave, a tall part that limits fixture support, or a polarity marking that is easy to miss once the board is populated.

How Should You Choose Between Wave, Selective and Hand Soldering?

When Is Wave Soldering the Practical Choice?

Wave soldering suits groups of compatible leaded components placed on a board with a clear solder side and a stable process route. The board passes over a controlled wave so many joints can be made in one operation. It is often a sound choice for repeated DIP-style layouts, provided the layout accounts for component orientation, clearance, thermal demand and any areas that need masking or a carrier.

At PCBasic, the documented DIP flow includes component insertion, wave soldering and manual touch-up soldering. Its production information also lists AOI inspections before and after wave soldering. That sequence gives a PCB soldering service a practical way to check placement before the solder step and inspect joints before the board moves to the next station.

When Does Selective or Manual Soldering Add Control?

Selective soldering is useful when only a few leaded joints need processing or when nearby SMT devices make a full wave inappropriate. Manual soldering can handle small quantities, repairs and joints that need individual attention. The choice should follow the design and volume, rather than a fixed preference for one method.

Ask the supplier how each leaded component will be routed. A clear route identifies the insertion method, soldering method, expected touch-up work and inspection point. That matters for a PCB soldering service because a change in component spacing or a late BOM substitution can change the best process method.

What Must Be Locked Before You Request PCB Assembly and Soldering Services?

Which Files Prevent Build-Time Assumptions?

Release a complete manufacturing package: Gerber and drill data, BOM with approved manufacturer part numbers, centroid or placement data where relevant, assembly drawings, revision-controlled schematics and test requirements. For through-hole parts, make the component side, lead form, polarity, height and any hand-install instruction unambiguous. A supplier cannot reliably infer these details from a silkscreen reference alone.

Before sending an RFQ, use PCBasic’s PCBA file checklist to compare the released package with the inputs needed for fabrication, procurement and assembly. It reduces back-and-forth and gives the engineering review a stable basis for a DFM response.

Which Acceptance Points Protect the First Build?

Define what will be checked, not only what will be assembled. A first-article review should confirm the correct component, orientation, lead condition, solder-joint appearance and any specified electrical behavior. PCBasic documents IQC incoming material inspection, a first-article inspection system and MES-based production traceability. Its stated assembly and testing flow continues through visual inspection, functional testing, NG rework and pre-shipment QA.

That sequence helps teams turn a prototype into a repeatable release. When the board needs electrical proof, specify fixtures, programming steps, test limits, pass/fail records and handling for failed units. The PCBA testing and inspection capability is the right conversion point for aligning test scope with the product’s actual acceptance requirements.

How Can a Through Hole PCB Assembly Service Support a Cleaner Release?

What Should the Supplier Review Before Procurement Starts?

Give the supplier the design package early enough to review hole data, part availability, polarity markings, spacing, soldering access and test needs together. An early review keeps the release on schedule and makes the first build more predictable. PCBasic provides through-hole PCB assembly service within a one-stop PCBA flow that covers PCB fabrication, SMT, DIP, testing and final assembly. That scope is especially useful for mixed boards because one engineering discussion can connect the layout to procurement, assembly and test.

PCB assembly and soldering services should also provide a clear response when a part is unsuitable for the planned route. A professional review can recommend a fixture, a component-orientation adjustment or a different soldering method while the change is still manageable. This keeps the discussion focused on the design’s requirements and gives purchasing a clearer quote basis.

How Do Traceability and Test Close the Loop?

A sound release connects material inspection, first article, soldering controls and final test records. If an issue appears in early units, traceability makes it easier to identify the affected revision, component lot and process step, then correct the right cause. PCBasic’s self-developed digital systems cover MES, IQC and first-article inspection, while its documented production flow includes DIP AOI, functional testing and final QA.

For buyers, this makes the next step straightforward: share the package, identify the parts that carry mechanical risk, and state how the completed board will be accepted. To begin that discussion, contact PCBasic’s engineering team with the BOM, design files, quantity and test expectations. The resulting review is more useful than selecting a process from a generic checklist.

Conclusion

When choosing between THT and SMT, it ultimately comes down to the specific design and production requirements. For through-hole PCB assembly, what truly affects the stability of mass production are not only the types of components, but also the hole diameter and pin matching, assembly direction, soldering method, fixture requirements, as well as subsequent inspection and testing requirements.

If these conditions can be clearly defined before production and implemented through complete manufacturing documents, clear process routes, and practical acceptance criteria, THT is not just "soldering the components onto the board", but a repeatable and traceable manufacturing process. For mixed-technology PCBs, this early planning can also reduce last-minute adjustments during pilot production, making subsequent production more stable.

FAQs

Q1: Is THT PCB assembly always more reliable than SMT?

A1: No single mounting method is best for every component. THT PCB assembly is often appropriate where a leaded component must withstand insertion force, vibration or repeated cable handling. SMT can be the better fit for high density and small packages. Judge the mounting method by the component’s mechanical, electrical and assembly requirements.

Q2: Can one board use both through-hole and SMT components?

A2: Yes. Mixed-technology boards commonly use SMT for dense circuitry and through-hole parts for connectors, relays, transformers or terminal blocks. The assembly drawing should clearly define the placement side, the process order and any fixture or masking requirement so the soldering route is planned before production.

Q3: What should I include in an RFQ for a PCB soldering service?

A3: Include Gerber and drill data, BOM, assembly drawing, component specifications, quantity, revision, delivery requirements and test expectations. For a PCB soldering service, also state leaded-part polarity, height, lead-form instructions, selective or wave-solder constraints and the acceptance records you need for the finished boards.