Soldering Non-Sprung Interface Pins (IF-PI): THT Soldering and Wire Attachment
Introduction
The interface pins (IF-PI) from uwe electronic are solid, non-sprung contact pins. They serve as the mating counterpart to spring-loaded battery contacts and transmit charging and signal currents – up to 55 A depending on the version. Variants are available for THT and SMD mounting as well as with solder, crimp, and sleeve terminations, in diameters from approx. 1.07 to 7.0 mm and lengths from approx. 2.0 to 27.0 mm.
Because these pins contain no internal spring, the temperature restriction that governs spring-loaded contacts does not apply: there is no risk of relaxation of a spring material. The pins are solid turned or stamped parts made of copper alloy with a metallic surface plating and are therefore thermally non-critical – standard soldering processes can be applied without restriction.
Key difference from spring-loaded contacts: no temperature restriction required.
Non-sprung interface pins contain no spring whose preload could be reduced by heat input. Common reflow, wave, selective, and hand soldering processes (peak up to approx. 260 °C, soldering iron up to approx. 380 °C) can be used without special time limits.
Instead, the focus for these pins is on mechanically accurate positioning and on protecting the contact surface from flux, solder, and contamination.
What Matters Instead with Non-Sprung Pins
Because the thermal load is non-critical, the processing focus shifts to three other points:
- Cleanliness of the contact surface: the contact zone (the end face or outer surface that later touches the mating contact) must remain free of solder, flux residues, and cleaning agent residues. Contamination increases contact resistance and permanently impairs contact reliability.
- No solder wicking: capillary action can draw molten solder along the pin toward the contact surface. Solder volume, soldering time, and hole clearance should be chosen so that the solder stays confined to the termination area.
- Accurate, perpendicular positioning: non-sprung pins have no travel to compensate for tolerances. The mounting position (height, perpendicularity, pitch) therefore directly determines the contact geometry relative to the mating contact and should be secured with an assembly fixture or soldering jig.
THT Soldering into the PCB
For soldering leaded interface pins, the usual process parameters of electronics manufacturing apply without restriction (reference values for lead-free SAC solders; the actual profile always needs to be determined for the specific equipment and assembly):
| Method | Typical Parameters | Contact Time with Solder |
|---|---|---|
| Wave soldering | topside preheat 100–150 °C; solder wave approx. 250–260 °C | approx. 2–5 seconds per terminal |
| Selective soldering (mini-wave/nozzle) | local preheat approx. 100–130 °C; solder pot/nozzle approx. 260–270 °C | approx. 2–6 seconds per joint |
| Hand soldering (small batch/rework) | soldering iron approx. 350–380 °C (lead-free), depending on pin mass | approx. 3–6 seconds per terminal |
Preparation
- Check the hole diameter: for complete through-hole tinning, allow an annular clearance of typically approx. 0.1–0.25 mm relative to the pin diameter. Excessive clearance promotes solder fall-through; insufficient clearance prevents solder rise in the hole.
- For high currents: plan sufficient copper area and connection to inner layers – a solid pin can only exploit its cross-section if the PCB is able to carry the current onward.
- Use an assembly fixture or soldering jig to hold the mounting height and perpendicularity during soldering.
- Mask the contact surface or orient it so that it is not reached by the flux application or the solder wave.
Soldering Process
- Insert the pins and secure them in the fixture; ensure a uniform insertion depth across all pins.
- Apply flux (the entire solder side for wave soldering, only the specific joints for selective soldering).
- Preheat according to the table in section 3 – the full standard band applies here; no limitation as with spring-loaded contacts is required.
- Solder: pass the wave, or apply the nozzle/soldering iron until the hole is fully filled and wetted.
- Allow to cool and remove the assembly from the fixture only after the solder has solidified, so that the pin position is preserved.
- Clean flux residues according to your process specification – making sure no residues remain on the contact surface.
Soldering a Wire to Interface Pins
Interface pins with a solder termination (solder tab, solder cup, or solder pin) can be connected directly to a stranded wire – typical for charging cradles, adapter cables, and test fixtures. Since no spring needs protecting, you can work with the usual temperatures and a soldering time appropriate to the cross-section.
Required Tools and Materials
- Temperature-controlled soldering station, tip matched to the pin mass (use a substantial chisel tip for large cross-sections)
- Solder wire with flux core (lead-free SAC solder or Sn60Pb40 as required by your application)
- Fixture or small vise to hold the pin
- Wire stripper, heat-shrink tubing for strain relief and insulation
- Magnifier for visual inspection of the solder joint
Procedure
- Select a stranded wire matched to the pin's rated current and strip approx. 3–5 mm (for solder cups: match the strip length to the cup depth).
- Pre-tin the wire so that the actual soldering time on the pin stays short and the joint stays clean.
- Clamp the pin in the fixture – oriented so that the contact surface does not come into contact with solder or flux.
- Set the soldering iron to approx. 350–380 °C (the higher value for large cross-sections) and wet the tip with fresh solder.
- Heat the termination area of the pin until the solder flows reliably there; place the pre-tinned wire in position or insert it into the solder cup and feed solder until the joint is completely filled and brightly wetted.
- Remove the soldering iron and let the joint cool undisturbed – do not move the wire while it cools.
- Apply heat-shrink tubing over the joint for strain relief and insulation.
- Perform a visual inspection and a pull test on the wire.
Important Notes
Keep the contact surface clear: no solder, no flux, and no cleaning agent residues on the contact zone – with non-sprung pins this is the single most important quality factor.
Limit solder wicking: size the solder volume and soldering time so that solder does not travel by capillary action toward the contact surface.
Secure the mounting geometry: non-sprung pins do not compensate for tolerances – fix mounting height, perpendicularity, and pitch with a fixture and verify them after soldering.
Account for the cross-section: for pins rated for high currents, plan sufficient thermal power and soldering time so that no cold joints occur.
Quality Control After Soldering
- Visually inspect the solder joints: complete through-hole tinning or a fully filled solder cup, shiny, no cold joints
- Contact surface visually free of solder, flux, and residues
- Mounting height, perpendicularity, and pitch of the pins verified against the drawing
- For wire terminations: pull test on the wire without the joint separating
- If required: measure the contact resistance of the finished connection
Summary
| Aspect | Non-sprung interface pins (IF-PI) | For comparison: spring-loaded contacts |
|---|---|---|
| Temperature limit | no component-side limit, standard processes permitted | approx. 150 °C reference value for the spring steel |
| Reflow / wave | standard profile with no time limit | minimize time above 150 °C |
| Hand soldering | approx. 350–380 °C, soldering time per pin mass | approx. 330–350 °C, only 2–3 seconds |
| Critical factor | contact surface cleanliness, solder wicking, mounting geometry | thermal load on the spring |
Questions About Your Application?
Our technical team is happy to help you select the right interface pin and design your soldering process. An overview of the range – including the matching sleeves – is available at uweelectronic.de – Interface Pins.
