Quick answer
THT is a technique for assembling electronic components onto pcbs using metal pins that pass through holes and are soldered. It’s known for its simple assembly, durability in harsh conditions, and remains useful for certain applications despite the rise of SMT.
Table of Contents
What is THT (Through-hole technology)?
THT technology is the abbreviation for Through-hole technology and ＂thru-hole＂ . It is a technique used to assemble electronic components onto printed circuit boards (PCBs). The distinguishing feature of this technology is that the electronic components have metal pins, referred to as “THT components.” These pins pass through the plated-through holes (PTH) on the PCB and are joined to the PCB through soldering with tin. This completes the assembly of electronic components onto the PCB.
THT components are known for their simple structure, straightforward assembly process, and ability to withstand harsh conditions such as high temperature and humidity. The assembly of THT components can be done manually through soldering or using high-volume production techniques like 波峰焊(Wave Soldering) . Some THT components can even be assembled using automated Surface Mount Technology (SMT) techniques.
Although SMT technology has become increasingly popular in modern electronics manufacturing, allowing products to become smaller, lighter, and thinner, THT technology still finds application in student electronics experiments, small-scale maker projects, and products that require resistance to high temperature and humidity.
The characteristics of THT (Through-hole technology) packaging technology
Common THT (Through-hole technology) components can be broadly categorized into the following three types:
- THT-packaged electronic components
- THT-packaged integrated circuits (ICs)
- THT-packaged modules
The introductions are presented separately as follows:
THT-packaged electronic components
This is the most common type of THT (Through-hole technology) component, and it encompasses the commonly seen electronic components such as resistors, capacitors, and inductors. Each of these components has various types of THT packaging, which give them different characteristics. The diagram below illustrates some commonly encountered THT electronic components.
Here are images of some dual-ended and three-pin electronic components – resistors, capacitors, and bipolar transistors.
THT-packaged integrated circuits (ICs)
THT-packaged IC (Integrated Circuit) is also a common category in Through-hole technology. Depending on the required pins and dimensions of the IC, different packaging names are used. The table below lists some commonly used abbreviations for THT-packaged ICs for readers’ reference. The image below shows a photo of an DIP24 component.
| Package Name | # of pin | W*L*H (mils) | pitch (mils) |
| MDIP8 | 8 | 365*250*130 | 100 |
| MDIP14 | 14 | 755*250*135 | 100 |
| MDIP16 | 16 | 760*250*130 | 100 |
| MDIP18 | 18 | 900*250*155 | 100 |
| MDIP20 | 20 | 1026.5*260*130 | 100 |
| MDIP24 | 24 | 1260*280*130 | 100 |
| MDIP28 | 28 | 1450*540*150 | 100 |
| MDIP40 | 40 | 2056.5*550*145 | 100 |
Here are some photos of IC (Integrated Circuit) components in SOP8, SOP16, and SOP40 packages.
THT-packaged modules
There are many types of circuit modules packaged with THT (Through-hole technology).
THT-packaged modules Example －LED seven-segment display OPD-AD4010
Taking the LED seven-segment display as an example, the THT-packaged LED seven-segment display is assembled with the front side serving as the light-emitting surface and the back side connecting to the pins and PCB. The image below shows a model OPD-AD4010, which is a 0.4-inch high LED 14-segment display with two characters. In the image, you can see the light-emitting surface and the pin structure underneath.
THT-packaged modules Example －LCD Module with PIN for arduino photo
The scale of THT (Through-hole technology)
Comparison between THT 0.39″ character height single-digit 7-segment display and Type-C connector
On the left side of the image is the OPD-S3910 single-digit 7-segment display from OPTO PLUS LED corp with a character height of 0.39 inches. On the right side is a USB Type-C connector. By comparing the graphics, we can get a rough idea of the size of the 0.39-inch THT 7-segment display.
The assembly methods for common Through-hole technology (THT) components
THT (Through-hole technology) assembly methods can be broadly divided into two types:
- Directly connecting THT components using pins
- Assembling THT components onto a PCB
Let’s discuss each method separately.
Direct pin connection THT(Through-hole technology) components
Since almost all circuit components are available in THT (Through-hole technology) packaging, direct soldering of THT component pins is a convenient approach when dealing with relatively simple circuits. This method is commonly used in student circuit experiments or when prototyping in small quantities. Below is a tutorial video demonstrating the assembly of a 24V battery indicator light using a THT-packaged LED bulb and resistor. It provides a reference for the soldering process.
Assembly on a PCB board
The most common method of assembling THT (Through-hole technology) components on a PCB board is called wave soldering process. This article does not delve into the details of wave soldering. Below is a two-minute video found on the internet that demonstrates the wave soldering process. You can see that when the PCB passes through, a raised wave of solder touches the bottom edge of the PCB, completing the assembly. The second method of assembling THT components on a PCB board is by manually inserting the components into the PCB and using manual soldering techniques. This method is often used for low-volume production or when the number of components is small. For mass production, wave soldering is commonly employed.
THT (Through-hole technology) is also commonly known by several other names
THT (Through-hole technology), also known as through-mount technology, has various alternative names. Taking Taiwan as an example, for THT-packaged IC integrated circuit components such as DIP24, which have symmetrical dual-sided pins, these pins are also referred to as DIP packaging (Dual in-line package). THT components are commonly known as “DIP components”.
Furthermore, since THT components typically have extended pins (LEAD) outside of the component structure, these pins are often referred to as PIN pins. Sometimes, THT components are also referred to as “components with PIN pins”.
Additionally, as THT components are mostly assembled using wave soldering technology, they are sometimes referred to as “Wave Soldering components”.
THT displays cannot go through reflow soldering
Before comparing any optical specification, please confirm one process question first: does your production line use reflow or wave soldering? Through-hole LED displays are not compatible with the reflow process. If your line only has reflow, choose the SMD version of the display. This one answer decides the THT or SMD question before any other specification. THT displays are assembled by wave soldering for mass production, or by hand soldering for small quantities.
Wave soldering conditions
The recommended wave soldering conditions for THT LED displays are:
- Pre-heat: 100 °C or less, for 60 seconds or less, measured at the LED pins
- Solder bath: 260 °C maximum
- Peak wave temperature: 245–255 °C for 3 seconds (5 seconds maximum)
- One soldering pass only. Do not pass the board through the wave twice.
- Board layout: keep the display at least 5 mm from the PCB edge. For 90-degree bent-pin types, keep at least 10 mm.
Hand soldering and rework
Use a temperature-controlled soldering iron of 30 W or less. The reference conditions are 300 °C for leaded solder and 350 °C for lead-free solder. For blue, green, and white products, the limit is 280 °C for 3 seconds or less. Some datasheets specify stricter conditions, for example 15 W and 260 °C within 4 seconds. The datasheet of the selected part number always has priority.
For rework, finish within 3 seconds at 350 °C, and do not let the iron tip touch the copper foil.
Lead bending and storage
- Bend the leads before soldering, at room temperature. Keep at least 3 mm between the bottom of the lens and the bending or soldering point. Do not bend the same lead more than twice.
- Storage before opening: 30 °C or less and 60 %RH or less.
- After opening, THT displays have no floor life limit. SMD displays are different: they should be used within 4 weeks (MSL 2a), or baked before use.
- ESD: keep the workstation static potential at 150 V or less, and the line humidity at 40–60 %. InGaN products (blue, green, white) are the most sensitive.
THT or SMD? A short comparison
| Condition | THT | SMD |
|---|---|---|
| Production line | Wave soldering or hand soldering | Reflow soldering |
| Environment | High temperature, high humidity, vibration | Normal indoor use |
| Mechanical needs | Strong pin retention, panel mounting | Thin design (down to 3.1 mm), high density |
| Smallest standard digit height | 0.3 inch (OPx-30xx) | 0.2 inch (OPx-20xx) |
| Floor life after opening | No limit | 4 weeks (MSL 2a) or bake |
Conclusion
This article provides a concise explanation of the names and aliases of THT (Through-hole technology) components. It also shares three major types of THT components and a comparison table of their sizes. Finally, it briefly introduces two assembly methods for THT components. It is hoped that readers will gain a preliminary understanding of THT components after reading this article.
OPTO PLUS LED Corp. is a professional manufacturer of LED seven-segment displays specializing in LED display components. We offer standard SMD and THT LED seven-segment displays,THT LED Alphanumeric Display, THT LED dot-matrix displays, THT LED standard-product-customization and Full-customized THT LED displays. If you have any related requirements, please contact us via Sales@opledtw.com or through our contact form.
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