Header pins are versatile through-hole components used to make removable connections between printed circuit boards (PCBs) and wires or cables. They allow boards to be interconnected or provide test points for diagnostics. Soldering headers securely is essential for reliability. Desoldering damaged headers then allows replacement. This article provides best practices on hand soldering and desoldering header pins to achieve robust, reproducible connections.
Header Pin Overview
Headers come in single, double, and multi-row configurations up to 50 pins or more. Common header types:
- Male pin headers
- Female socket headers
- Straight and right-angle versions
- Single and double row
- Through-hole and surface mount styles
- Common pins sizes from 0.6mm to 1.27mm diameter
Headers are manufactured from tin-plated copper alloy leads inserted into a supporting plastic body. The plastic provides insulation between pins.
Soldering Header Pins
Follow these steps to hand solder headers to a PCB:
1. Prepare the Header Pins
- Check the header fits into the PCB holes without forcing. Reject if pins are bent or defective.
- Pre-tinning the header pins can improve solder flow but is not required if using rosin-core solder.
- For high temperature solders (over 275°C), pre-tinning may be needed to prevent damaging the plastic.
- Flux paste can be applied to pins and pads to aid solder flow.
2. Prepare the Board
- Clean any oils, contamination, or oxides from the header pads using isopropyl alcohol.
- Inspect pads under magnification to ensure there are no solder mask issues or open circuits.
- Apply solder paste to pads if not using rosin-core wire solder. Match paste alloy to wire alloy.
- Place the PCB on an ESD-safe work surface and secure with clamps or vise.
3. Insert the Header
- Carefully insert the header into the mating PCB holes without bending pins.
- Position the plastic snugly against the board surface.
- Ensure the header sits straight and flat against the board.
- Visual alignment marks aid placement for polarized headers.
4. Tack Solder Each Pin
- Use a small, clean soldering tip suited to the pin pitch. Conical tips work well.
- Set iron temperature for the solder alloy used. 300-375°C is typical.
- Lightly tack one pin on each end first to temporarily hold the header in place.
- Solder remaining pins on one side with 1-2s heat per joint. Avoid bridging between pins.
- Flux reduces bridging risks. Clean tip frequently.
- Inspect each joint under magnification after soldering. Reflow if needed.
5. Finish Soldering
- Solder remaining pins on the opposite side of the header using the same technique.
- Recheck all pins for full fillets, no bridges, and straight alignment.
- If pins shift during soldering, reheat and realign.
- Clean flux residues if needed with isopropyl alcohol.
6. Post Solder Inspection
- Use an inspection microscope to carefully check each joint around the entire header.
- Reflow and resolder any joints with insufficient wetting, voids, or other defects.
- Confirm there are no solder bridges between adjacent pins.
- Headers should remain fully aligned without tilting or raising from the board.
Following this systematic soldering process will produce reliable, trouble-free header connections.
Desoldering Header Pins
Desoldering may be needed to replace a damaged header or change the configuration. Use the following process to safely desolder headers:
1. Clean Header Joints
- Remove any conformal coating from the header area using alcohol or coating stripper.
- Thoroughly clean solder joints of contaminants with degreaser. Flux remover can also be used.
2. Pre-Heat the Header
- Set the soldering iron tip temperature to ~350°C.
- Apply heat simultaneously to the header plastic and a few pin joints.
- Gradually increase temperature to avoid damaging plastic.
- Heat both sides of header to evenly pre-heat all joints.
3. Desolder Each Joint
- Using a narrow conical desoldering tip, apply heat to melt each solder joint.
- Simultaneously use a desoldering pump or wick to remove the liquefied solder.
- Take care not to apply excess force that may lift pads or damage plated-through holes.
- Desolder one side of header completely before moving to the other side.
4. Remove the Header
- Once both sides are fully desoldered, the header will detach easily from the board.
- Elevate pins on each end alternately to gradually walk the header free.
- If a short stub remains in a plated hole, use a desoldering tip to remove it.
- Do not force or pound on the header which can damage the board.
5. Clean and Inspect
- With header removed, thoroughly clean solder residue from pads using wick, pump, or cleaning solution.
- Inspect each pad under magnification to ensure there are no lifted or damaged pads or holes.
- Alcohol cleaning and mild abrasion can remove stubborn residues.
The board is now ready for a new replacement header to be soldered in place.
Hand Soldering Technique
Follow these techniques to hand solder headers successfully:
- Use a temperature controlled iron or station for consistency.
- Match tip size to pin pitch to minimize bridging.
- Tinned copper tips transfer heat efficiently over untinned alloy tips.
- Apply the minimum heat needed to reflow the joint to avoid damaging plastic or PCB.
- Keep the soldering iron clean and tinned. Wipe frequently on a damp sponge.
- Quality no-clean flux cores promote excellent solder flow and wetting.
- Inspect every joint thoroughly under magnification after soldering.
- Adjust process based on results – more heat, flux, or time if needed.
Good hand soldering skills take practice but are essential for quality PCB production.
Problem: Solder bridges between pins
Solution: Use smaller tip, lower heat, less solder, and flux to prevent bridges. Inspect closely and clean any bridges with braid.
Problem: Cold solder joints
Solution: Increase heat or time to properly reflow joint. Flux and pre-tinning also helps. Rework unsoldered joints.
Problem: Pins lifting pads or shifting
Solution: Avoid putting lateral stress on pins during soldering. Remove and realign crooked pins.
Problem: Solder not wetting to pin
Solution: The pad or pin may be oxidized. Clean and reapply flux before resoldering.
Problem: Cracked or damaged plastic
Solution: Reduce soldering temperature and pre-heat plastic before soldering to avoid thermal shock.
Problem: Desoldering damage
Solution: Carefully pre-heat before desoldering, and never force or pound on the header which can damage the board.
- Use written procedures for hand soldering
- Train operators on process requirements
- Audit workmanship frequently under microscope
- Document all process parameters
- Record solder wire and flux batch used
- Track oven profiles and iron tip temperatures
- Link parameters to individual boards and lots
- Log any defects discovered
- Analyze defects for root cause
- Optimize parameters to reduce defects
Controlling the soldering process improves yields, lowers rework, and ensures consistent header connections.
Frequently Asked Questions
What is the most common header pin diameter?
Is it always necessary to pre-tin header pins?
Pre-tinning can help solder flow but is not essential if using a rosin-core solder and proper technique. It may be needed for solder alloys requiring higher temperatures.
What causes header pins to become crooked during soldering?
Applying uneven lateral stress, improper hole clearances, misaligned pins, or poor solder joints can all cause pins to shift out of alignment during soldering.
Can solder flux damage a PCB?
Yes, acidic flux can corrode copper pads and traces if not cleaned after soldering. Use no-clean flux designed for electronics. Clean any pastes or residue after soldering.
What is the benefit of breadboarding a header first?
Breadboarding allows checking the header fits and functions properly before permanent soldering. Doing so avoids potential rework if issues are found.
Soldering header pins onto PCBs requires following good hand soldering practices. Using the proper techniques and controls for heating, wetting, fluxing, and pin alignment minimizes defects like bridges and tombstoning. Similarly, careful desoldering prevents damage to the board. Consistent quality soldering produces durable, reliable header connections able to withstand vibration, shock, and repeated mating cycles over the product lifetime.