Through-Hole Assembly Capabilities & DFM Checklist

THT is straightforward, Through‑hole assembly (also known as THT – Through‑Hole Technology) is a key PCB assembly method where components with leads are inserted into drilled holes and soldered for robust electrical and mechanical connections. This article breaks down clearly THT PCB assembly capabilities and provides a practical THT DFM review checklist that should be verified before manufacturing by KnownPCB.

What is the Through-hole assembly?

The core of THT (Through-Hole Technology) is about threading component leads through pre-drilled vias. To put it simply, imagine you are taking leaded components, popping them into pre-drilled holes in the PCB, then moving to the next step to solder them down. The electrical connectivity and solid mechanical anchoring are achieved in one go. The whole workflow is the classic “plug-then-solder”. However, please don’t confuse THT with SMT (Surface Mount Technology). SMT is a “place-solder” model, which is distinct from “plug-then-solder”.

Core features of THT （Through-Hole Technology）:

The components pass through the PCB to form via plated-through holes (PTH), enabling strong electrical and mechanical connections.
Soldering occurs on the back side of the component leads and pads, achieving double-sided mechanical anchoring.
It’s the go-to choice for applications requiring high mechanical strength, high power, and high reliability, such as connectors, transformers, and power modules.

Key Manufacturing process of THT （Through-Hole Technology）

Process	Describe	Standard Basis
Drilling	Through holes are machined using a CNC drilling machine, with a diameter accuracy of ±0.01mm, to accommodate component leads.	IPC-A-610H 8.2.1
Hole metallization	The hole walls are thickened by chemical copper plating followed by electroplating (25–50 μm) to form conductive pathways, enabling interconnection of inner layers in multilayer boards.	IPC-J-STD-001J 4.5.2
Component insertion	- Axial leads: Resistors, diodes, leads extend along the axis, horizontal mounting. - Radial leads: Capacitors, LEDs, leads extend vertically, saving space. - DIP/SIP packages: Commonly used dual in-line/single in-line packages for integrated circuits, positioned by automated insertion machines.	IPC-A-610H 8.1.1–8.1.3
Pin cut	After soldering, trim any excessively long leads, leaving 0.5–1.0 mm of protrusion.	IPC-A-610H 8.2.4
Welding	- Wave soldering: The mainstream method for mass production, where molten solder is applied to the bottom of the PCB through a wave of solder. - Manual soldering: Used for small batches, rework, or high-power components (such as transformers and connectors). - Selective wave soldering: Precisely sprays solder, suitable for mixed SMT and THT boards, reducing heat damage.	IPC-J-STD-001J 5.3.1–5.3.4

Through-Hole Assembly Capabilities & DFM Checklist

KnownPCB Through-hole Assembly Process (Wave soldering)

Technical Specifications

Submit Your Throguh-Hole PCB Project

Item	Sub-item	Standard Capability	Limited Capability
DIP Process (Wave soldering)	PCB Size - Min Size	L≥30mm, W≥30mm	L<30mm
	PCB Size - Max Size	L≤650mm, W≤400mm	L:800-650mm, W:400-450mm
	PCB Size - Thinnest Size	0.4mm	T < 0.4mm
	PCB Size - Thickest Size	5mm	T > 5mm
Conformal Coating Process	Temperature range	-30℃ ≤ T ≤ 120℃	-50℃ ≤ T ≤ 150℃
Conformal Coating Process	Coating thickness	20um ≤ T ≤ 35um	35um ≤ T ≤ 60um

DFM Review Key Points for THT (Through-Hole Technology) PCB Assembly | KnownPCB

Before sending your PCB to manufacturing, the following DFM review points must be checked to ensure reliable THT assembly and optimal yield.

THT Drill Size Consistency
- Ensure that all THT drill sizes are ≥ 0.3mm to avoid confusion with SMT blind/buried vias.
- Reduce drill bit replacement costs with standard hole size groups (e.g., 0.6 / 0.8 / 1.0 mm).
Spacing Between Pads and Traces
- The THT pad should be ≥ 0.3 mm from adjacent traces to prevent wave bridging.
- It is recommended to add teardrop to the pad for high-power components to enhance connection strength.
Component Layout Orientation
- DIP ICs are arranged in a uniform direction for automatic plug-in machine feeding (high-speed automatic insertion).
- This prevents localized thermal stress and uneven heat distribution caused by clustering large components.
Wave Soldering Shadow Area
- Avoid placing THT solder joints behind tall components (e.g., electrolytic capacitors) to prevent solder obscuration.
- Using selective wave soldering mitigates this issue.
Test Point Allocation

Assign THT test holes (0.9–1.0 mm diameter) for critical signals to facilitate flying probe testing.

Typical Application Scenarios for Through‑Hole Assembly

Applications	Typical Components	Technical Advantages	Standard Basis
Industrial control equipment	Power connectors, relays, terminal strips	Strong vibration and shock resistance; mating/unplugging cycles > 750 times	IPC‑A‑610H 8.1.1
Automotive electronic systems	Motor controllers, ECU power modules, high‑current connectors	High mechanical strength; good thermal cycling stability	IPC‑A‑610H Class 2/3
Power & Power Modules	Transformers, inductors, high‑power electrolytics	High current capacity and reliable heat dissipation	IPC‑J‑STD‑001J 5.3.2
Military & Aerospace	Radar, navigation, satellite power systems	Extreme environmental adaptability; long‑term reliability	NASA‑STD‑8739.3 13.6.2
Medical equipment	ECG monitors, defibrillators, diagnostic interfaces	Low failure rate; repairable solder joints	IEC 60601‑1 + IPC‑A‑610H
Communication base stations	RF filters, high‑power amplifiers	High power density; excellent thermal expansion match	IPC‑A‑610H 8.2.4