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What is Through-Hole Reflow Soldering [2024 Updated]

through-hole reflow
PCBONLINE Team Wed, Oct 30, 2024
250
through-hole reflow PCBA

Through-hole (PTH) components are usually soldered to the PCB by wave soldering. However, here's an alternative option - through-hole reflow soldering available for PCB assembly with PTH components.

Explore what through-hole reflow soldering is now!

Overview of Through-hole Reflow Soldering Technology

Through-hole reflow soldering, also called pin-in-paste reflow, is a PCB assembly technology that assembles the through-hole (PTH) components with the pick-and-place and reflow SMT (surface-mount technology) processes.

through-hole reflow soldering

You can see the through-hole reflow or pin-in-paste assembly process below:

through-hole reflow process
  • Step 1. Fabricate the PCB with plated-though holes.
  • Step 2. On the SMT line, transfer the PCB under the SMT stencil.
  • Steps 3-4. In the solder paste printing machine, the scraper pushes the solder paste through the SMT stencil holes to fill the PTH holes.
  • Steps 5-6. In the component pick-and-place machine, the PTH components with the SMDs are sucked by the nozzles to place on the PCB. If it cannot, after placing the SMD components, a technician will manually insert the leads of the PTH components through the PCB holes. Part of the solder paste will stick onto the PTH component leads, but most remain in the hole.
  • Steps 7-8. In the reflow soldering oven, all the SMDs and through-hole components are soldered tightly to the PCB. The solder paste in the hole and on the lead melts and forms the IMC (intermetallic compound) with the PCB copper wall and pad.

Through-hole reflow soldering provides reliable connections between the PTH component and the PCB board. It utilizes heat to melt solder paste applied to the leads of components.

Why do we use through-hole reflow soldering for electronics assembly? Cost reduction is the reason.

For PCB assembly projects, SMDs (surface-mount devices) account for about 80% of the component costs, but SMT assembly accounts for only 60% of the assembly fees; through-hole components account for about 20% of the component costs, but PTH assembly accounts for 40% of the assembly fees.

That's why the project developers and electronic manufacturers consider through-hole reflow, as with it, all the PCB components can be mounted on only the SMT lines.

By working with a PCBA manufacturer PCBONLINE that provides through-hole reflow, you can save big, as all the components can be soldered on the PCB on the surface mount assembly (SMT) line!

What to Take Care for PCB Though-hole Reflow?

Though pin-in-paste reflow saves big and is efficient, it has many requirements. You will need to consider the below aspects for through-hole reflow PCBs.

Solder paste filled in the PCB hole rate -- The solder paste in the PTH hole should be at least 75%.

Standoff design -- In PCB design for through-hole reflow, the PCB pads should be designed to accommodate the thermal and mechanical stresses during reflow, ensuring strong solder joints. Between the PTH component and its soldering pad, a standoff should be designed to increase the solder paste printing amount. What's more, the standoff can prevent the solder beads between the PCB and the PTH component.

PTH component requirements -- The PTH components for pin-in-paste reflow should be able to withstand the lead-free reflow soldering temperatures (260°C, 10 seconds). Besides, as the PTH components are picked and placed automatically, they had better be in the tape-on-reel package.

Via diameter -- The PCB hole diameter should ensure the solder paste flows into the hole and the reliability of the assembly. It depends on the lead's maximum diameter and effective diameter and the shape of the PTH component lead end.

pin in paste diameter
  • Flat-end lead: effective lead diameter = 100% maximum lead diameter
  • Round-end lead: effective lead diameter = 75% maximum lead diameter
  • Sharp-end lead: effective lead diameter = 50% maximum lead diameter
  • Reliability: For military and aerospace electronics that should withstand some mechanical strength, through-hole reflow had better not be used for PCB assembly as its reliability is not as good as wave soldering.

One-stop PCBA Manufacturer PCBONLINE

If you need PCB assembly for your project, no matter what technology is required, including surface-mount assembly, through-hole reflow, nitrogen reflow, wave soldering, and selective soldering, you can have your project manufactured at PCBONLINE from an initial idea to PCBA and box-builds under one roof. for one-stop EMS (electronic manufacturing service) solutions from prototypes to mass production.

PCBA manufacturer PCBONLINE

PCBONLINE is a PCBA source factory manufacturer, having two large advanced PCB manufacturing bases, one PCB assembly factory, stable supply chains, and an R&D team. Besides, it has strategic cooperation with the top 3 mold and enclosure manufacturers in China. It also sources all components for PCB assembly from the original component factories and first-level suppliers.

Advantages of PCBONLINE in through-hole reflow and PCB assembly

The SMT lines at PCBONLINE's PCB assembly factory can handle both SMT assembly and through-hole reflow.

PCBONLINE offers free DFM (design for manufacturing) for all PCBA projects, including the Gerber, BoM (bill of material), testing files, and solving all technical and unexpected issues during prototyping to ensure successful and smooth production for massive PCB assembly.

One-stop PCBA manufacturing meeting your custom demand, including R&D, prototype/sample, component sourcing, PCB assembly, PCBA value-added, enclosures, and box-build assembly.

When your project goes to the mass production stage, PCBONLINE will refund you the fees for R&D, prototypes/samples, and PCBA functional testing.

High-quality PCBA manufacturing certified with ISO 9001:2015, ISO 14001: 2015, IATF 16949:2016, RoHS, REACH, UL, and IPC-A-610 Class 2/3.

No matter what quantity of boards you want, PCBONLINE provides one-on-one engineering support throughout the project. To get a quote for your project, contact info@pcbonline.com.

Conclusion

Through-hole reflow soldering can replace wave soldering in many situations, especially for high-density PCBs. At the one-stop PCBA manufacturer PCBONLINE, SMT assembly, through-hole reflow, and wave soldering are available. If you want PCBA manufacturing or have problems with through-hole reflow PCBs, don't hesitate to chat with us from the online chat window.

© 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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