When confronted with insurmountable danger, the great heroes of literature and the cinema often respond boldly by asserting, “don’t worry, we’re not dead yet.” Afterward, they somehow miraculously escape their certain demise and go on to win the day until the inevitable sequel comes out. However, in the world of printed circuit board design, we rarely experience that level of excitement, with the following exception; the through-hole component, which isn’t dead yet.
Once surface-mount technology became the preferred package type in circuit board design and manufacturing, the downfall of older through-hole parts was all but certain. But just like 007, these parts refuse to go quietly into the night and continue to serve a vital need in circuit board assemblies. Here are some of the advantages of through-hole technology and why these components are still an essential part of the electronics industry.
The Popularity of Surface-Mount Components
The majority of electronic components assembled onto printed circuit boards today are surface-mount technology parts. The metal leads of these components are typically held onto their corresponding metal landing pads on the board with solder paste. Not only does the solder paste temporarily hold the parts in place, but once heated in an industrial oven, it will melt and “reflow,” soldering the leads to the metal pads.
There are several advantages to using SMT parts, which is why they have become the dominant package style for PCB assembly:
- Component size: The leads can be longer than the actual part for some through-hole components such as resistors and capacitors. Not only does this take up more room for packaging and shipping, but it also takes up more space on the circuit board. In comparison, multiple SMT parts of the same type can often fit into the same space of a single through-hole component.
- Electrical performance: The smaller package sizes and leads of SMT parts reduce the total length of the signal path on the circuit board. In high-speed and high-frequency designs, this will help improve the board’s signal integrity, leading to better electrical performance.
- Part cost: With less physical material needed to manufacture a component, the cost-per-part of an SMT component can be significantly less than the same part in a through-hole package.
- Availability: With the advantages of surface-mount packages, many through-hole component types have now been completely replaced with their equivalent SMT packages.
- Installation: Most through-hole parts have to be manually inserted for wave soldering, which is more time and labor-intensive than the automated assembly processes available for SMT components.
It is easy to see why the SMT package style has become so popular for circuit board manufacturing. But, as we will soon see, there are still plenty of advantages to using through-hole technology parts.
The Advantages of Through-Hole Technology
Through-hole components are still an essential part of circuit board manufacturing, and to illustrate this, we will break it down into two categories: design and manufacturing.
One of the chief advantages of through-hole parts is their strength. A surface-mount part is soldered to a metal pad, and while this provides a solid bond between the part and the board, it isn’t nearly as strong as a through-hole connection. With the through-hole lead passing through a hole and the solder wicking up and through, the part has a much more robust solder joint. This strength is essential for switches, battery holders, connectors, and other interfacing parts that will be under a lot of stress during normal use.
Another through-hole advantage is for designs with a lot of power. High-current circuits need a large, strong solder connection to their traces on the board, and a surface mount solder joint may not be enough. Additionally, high-powered parts can also be very heavy, especially when a heat sink is used. Not only do these parts need the strength we mentioned above, but the amount of heat needed to solder them in place may be too much for a surface-mount solder joint. Also, many larger parts for high-powered applications simply aren’t available in an equivalent surface-mount package for the reasons that we have just listed.
While it is true that surface-mount parts are ideal for automated assembly processes, it is much easier for manufacturing technicians to solder a through-hole component manually. This makes through-hole parts an attractive alternative for prototype builds and other limited volume production runs that require hand soldering. Through-hole components are also easier to rework if components need to be desoldered for corrections or replacement. And of course, a through-hole part is better for a DIY project, whether at home or in the office.
Although surface-mount parts will make up most components used in circuit board manufacturing, there is still a vital need for through-hole parts. These components are not dead yet and will continue to play an important role in circuit board manufacturing for a long time to come. For example, another essential need for through-hole parts is in legacy designs. Many of these circuit boards must be built according to copy exactly requirements to ensure that there isn’t any deviation in how the board functions. The components used in the assembly of PCBs governed by copy exactly rules must match those they were originally designed with, or the entire design will have to be re-validated. Not only is re-validation time-consuming, but it is expensive too.
Get the Help You Need to Make the Right Component Selection
So what is the right type of component package to use on your board? The answer is; it depends on the design, the volume of boards to be built, and the production method to be used. Fortunately, some good help is available to you for the right answers in your PCB contract manufacturer. These people have spent years helping designers to choose the best parts for their designs with the following resources:
- Component engineers to help you make part determinations based on need and application
- Design engineers to help with part changes and circuitry modifications for the best electrical performance of the design
- Manufacturing engineers to help with part choices for efficient production processes
- Procurement specialists to find the best prices, availability, and genuine, high-quality parts during supply chain shortages
At VSE, we have been helping our customers with their component selections for well over 30 years, and we have a reputation for getting the job done right. We can help you identify which through-hole components will be the best fit for your design and answer your design and layout questions surrounding these parts simultaneously.