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Selective Soldering vs Wave Soldering for Through-Hole PCB

PCBONLINE Team

Thur, Sept 29, 2022

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How to solder through-hole PCBs for original equipment manufacturers and business makers? Hand soldering is not suitable due to the quality and efficiency requirements. There are two through-hole PCB assembly techniques -- selective soldering and wave soldering.

Both selective soldering and wave soldering are available at PCBONLINE's PCB assembly factory. Which through-hole soldering method is the best for your PCBA manufacturing project? Check what selective soldering and wave soldering are, and their pros and cons, and you can find the best soldering technique.

Part 1: What is Selective Soldering

selective soldering

Selective soldering, also known as selective wave soldering, is a through-hole PCB assembly technique for high-end applications.

Usually, selective soldering serves through-hole PCBs used for medical, military, and automotive fields, where high reliability and long shelf life are required.

Selective soldering is developed from wave soldering and also involves two stages -- preheating and soldering. And it also happens after SMT assembly. But unlike wave soldering, jigs are not required for selective soldering.

Selective soldering can be classified into off-line selective soldering and on-line selective soldering. At the PCBA manufacturer PCBONLINE, our Ersa selective soldering machine is the on-line type, which contains a flux spraying module, a preheating module, and a soldering module, and achieves automotive through-hole soldering.

selective soldering

In the flux spraying system, flux is sprayed accurately only on the PCB joints that need welding. Where to spray and how much to spray depends on the program set up by our CAM engineer. It reduces the flux amount in use and prevents flux to pollute the other areas.

In the preheating module, the whole PCB assembly board is warmed up homogeneously. Solder flux activates through preheating, and electronic components on the PCBA are also preheated so that the thermal-sensitive components won't be damaged from soldering temperatures.

In the solderingmodule, tin flow rushes out from a nozzle to weld the component's pin with the PTH hole walls. A nozzle serves only a joint each time. There is a nitrogen protection device beside the nozzle to prevent the occurrence of tin dregs.

When to use selective soldering for through-hole PCB?

Selective soldering is suitable for small and middle scale PCBA production of high-value-added products, especially when there are thermal-sensitive components. The soldering temperature reaches 260℃, and jigs for wave soldering can't protect thermal-sensitive components. In such a case, selective soldering is the cure.

The other situation is when the through-hole joints require custom soldering specs. As different through-hole components and joints may have different pin distances and heat capacities, they have different through-tin requirements. Selective soldering enables the PCBA manufacturers to set up the tin flow speed, soldering time, and wave height custom to the through-hole joint and PCB thickness.

What are the pros and cons of selective soldering?

  • Pros: custom soldering specs for each through-hole join, 0 soldering defect, a small thermal shock to the PCBA, less flux residue on the PCBA, more cleanness of the PCBA, saving flux, doesn't need jigs, reducing the use of nitrogen, low machine maintenance cost
  • Cons: low efficiency of through-hole soldering, only suitable for the small and middle scale of production, high soldering cost due to the expensive machine

Part 2: What is Wave Soldering

Wave soldering is the most common through-hole soldering technique, and it is suitable for bulky PTH PCB assembly. It is half-automatic because it requires the technician to install the PCBA in a jig.

Jigs are necessary for wave soldering. The jigs are custom fabricated for the PCBAs that need soldering, and they cover the areas that don't need wave soldering. When a PCBA is put in the jig, only the through-hole joints are exposed.

Unlike selective soldering, wave soldering is a one-time job. It solders all the through-hole joints at a time. Though wave soldering has high efficiency, it forces the PCBA manufacturer to make a balance between different soldering requirements of through-hole joints.

wave soldering machine

Wave soldering involves two stages -- preheating and soldering. Flux is sprayed to all the through-hole joints. In the preheating stage, the whole PCB is warmed up to activate the flux and preheat the board and components. In the soldering stage, the PCBA put in the jig is soaked in the tin flow to weld the through-hole component pins and the hole walls.

After wave soldering, the moving conveyor belt brings the PCBA with jigs out from the wave soldering oven. Technicians take out the PCBA and clean away the flux residue, and usually, they have to visually check the PCBA and add tin through hand soldering. The reason is that the jig may affect some areas from being soldered.

When to use wave soldering?

Wave soldering is suitable for large-scale production of PCBAs used for common applications without too strict quality requirements.

From the one-stop PCBA manufacturer, wave soldering we provide is the lead-free type.

What are the pros and cons of wave soldering?

  • Pros: cost-effective, high-efficiency
  • Cons: requiring jigs, relatively large thermal shock, requiring hand soldering to add tin, large use of flux and nitrogen, high machine maintenance cost

Part 3: Selective Soldering vs Wave Soldering

PCBONLINE provides both selective soldering and wave soldering for through-hole PCBs. You can check the selective soldering vs wave soldering comparison table below.

Selective soldering
Wave soldering
Soldering reliability
High
Normal
Requiring jigs or not
No
Yes
Soldering method
Tin flow rushes out from a nozzle to weld each time
The PCBA in a jig to soak in tin flow to weld all through-hole joints at one time
Soldering cost
High
Low
Production scale
Small and middle scale
Large scale

Part 4: Most Cost-Effective One-Stop PCBA Manufacturer -- PCBONLINE

PCBONLINE, founded in 1999, has two large advanced PCB manufacturing bases and one PCB assembly factory. From PCBONLINE, you can not only order through-hole PCB soldering including selective soldering and wave soldering, but also PCB fabrication, SMT assembly, electronic component sourcing, and box build assembly.

PCB assembly services PCBONLINE

What are the benefits you can enjoy by working with PCBONLINE for through-hole PCB soldering?

    • Our PCB assembly factory provides selective soldering, wave soldering, and SMT soldering following IPC-A-610 Class 2/3 standards.
    • PCBONLINE provides freePCB design for manufacturing, PCBA design for assembly, and box build design for excellence.
    • We can work in the daytime and overnight for PCBA manufacturing for expedited orders, and the fastest lead time is 8 hours.
    • Transparent and fair PCB assembly pricing, one-on-one considerate customer support.
    • Besides SMT and through-hole assembly, we provide conformal coating, IC programming, functional testing, and burn-in testing for PCB assembly.

We are an ISO, IATF, REACH, UL, and RoHS private-own source factory manufacturer for PCB, PCBA, and box builds. If you need our services, you can send your Gerber and BOM to us by email at info@pcbonline.com to get a quick quote. Our engineers will make sure your design is optimum for fabrication.

Conclusion

Selective soldering achieves automatic through-hole soldering custom to each joint that needs soldering. Wave soldering is the traditional through-hole soldering method and solders all through-hole joints at one time. Each through-hole soldering method has its pros and cons, and you will need to choose the appropriate soldering method based on the soldering requirements of your PCBA and your budget. If you have any questions or doubts about through-hole PCB soldering, welcome to chat with us online or send emails to us.


©This article is an original work of the PCBONLINE team. Please indicate the author PCBONLINE if you reprint. If the article is reproduced without permission or indicating the author's source, PCBONLINE reserves the right to investigate the infringement.

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