How to Solder Wire on Circuit Board: Mastering the Basics

September 20, 2023

Table of Contents

Introduction to Soldering Wires on Circuit Boards

Soldering wires onto circuit boards is essential for anyone working with electronics. While it may seem daunting initially, soldering is easy to learn with essential knowledge and practice.

This comprehensive guide will teach you everything you need about soldering wires on circuit boards, from beginner tips to advanced techniques.

Soldering joins two metallic surfaces using a filler metal that melts below 450°C. In electronics, soldering is used to electrically and mechanically connect component leads to pads on the circuit board.

The most common solder is an alloy of tin and lead, which melts at around 185°C. When the solder melts, it wets and fuses the metallic surfaces upon cooling and solidification. This creates a solid conductive joint.

Soldering is essential for assembling and repairing circuit boards. Here are some key reasons why soldering is essential:

Forms electrical connections: Soldering connects tracks, and component leads on the board to pass signals and power.
Provides mechanical support: The solder joint offers adhesion and strain relief for components mounted on the board.
Allows efficient assembly: Soldering enables automated mass production of PCBs by soldering components.
Enables modifications: Soldering allows you to remove, add, or replace components on a populated board.
Used for repairs: Fixes broken joints, replaces damaged tracks, or lifts components off boards.

With the basics covered, let’s learn how to solder wires onto circuit boards step-by-step.

Gathering the Required Tools and Materials

Soldering wires on circuit boards requires just a few basic tools and materials. Here is the essential equipment you’ll need:

Soldering Iron

The essential tool is the soldering iron, which provides controlled heat to melt solder. Choose an iron with an adjustable temperature between 300-400°C. Opt for a fine tip around 1mm to 2mm for soldering wires. More extensive tips are better for heavy components.

Solder Wire

Solder wire provides the filler metal to form joints. Standard rosin-core solder with a 0.5mm to 1mm diameter is ideal. Lead-free solders require higher iron temperatures.

Soldering Stand and Sponge

A soldering iron stand safely holds the hot iron when not in use. The sponge is used to clean and tin the iron tip.

Flux and Cleaner

Flux removes surface oxides and facilitates solder flow. Isopropyl alcohol cleans flux residues after soldering.

Safety Gear

Use safety glasses to protect your eyes from splatter. Work in a well-ventilated area to avoid inhaling fumes.

That covers the essential tools. Additionally, helpful items include tweezers, wire cutters, helping hands, fume extractors, and desoldering braid. You can start with the basics and expand your toolkit as you gain experience.

Preparing Wires and Boards for Soldering

Proper preparation is critical to achieving good solder joints. Follow these steps to set up wires and circuit boards before soldering:

Cut wires to length: Cut stranded or solid core wires to the required length with some extra to insert into holes.
Strip insulation: Use wire strippers to remove around 1⁄4” to 1⁄2“of insulation from wire ends. Take care not to nick the strands.
Tin wire ends: Pre-tinning wires with a thin solder layer ensure proper heat transfer and joint formation.
Clean board: Use isopropyl alcohol to clean solder pads and holes on boards to remove grease and oxides.
Secure boards: Fix boards in a vise or clamping stand. This leaves both hands free for soldering and avoids accidental movement.
Position components: Insert all parts, like headers and connectors, in their correct positions on the board.
Heat sinks: Attach heat sinks to protect heat-sensitive components near solder points.

With all wires and boards prepped, you are now ready to move on to soldering. Proper preparation leads to quick and clean soldering.

Step-by-Step Guide: How to Solder Wires on Circuit Boards

Follow these step-by-step guidelines when soldering wires to any circuit board:

Tin the Soldering Iron Tip

Keeping the iron tip tinned improves heat transfer and allows you to apply solder to joints quickly. To tin the tip:

Apply a small amount of solder directly to the hot iron tip.
Spread the solder evenly until the tip is coated smoothly.

Position and Bend the Wire

Correctly inserting and securing the wire in place is critical before soldering. Based on board type:

For boards plated through holes, insert the wire from the component side.
For single-sided boards, wire is inserted from the solder side.
Bend the protruding wire slightly to hold it in place before soldering.

Heat the Pad and Wire

Simultaneous heating of both surfaces improves joint integrity. When heating:

Place the tinned iron tip simultaneously on the pad and wire lead.
Heat both for around 2 seconds until the wire and pad are hot enough.
Avoid moving the wire while heating, as this weakens the joint.

Feed Solder to the Joint

With pad and wire at temperature, apply solder for a clean joint.

Touch the solder to the pad and wire close to the iron’s tip.
The solder will melt and flow smoothly around the wire and pad at temperature.
Use just enough solder to fill the joint.

Allow the Joint to Cool, and Inspect

Finally, let the joint solidify fully before inspection.

Remove the iron tip and allow the solder joint to cool undisturbed for a few seconds.
Inspect that the joint has formed correctly with solder fillets around the wire.
Reheat and rework if the joint looks cracked or has cold spots.

The brief descriptions help set the context before listing the steps. Let me know if you want me to revise any other sections this way.

Helpful Tips for Beginners

Here are some additional helpful tips for beginners learning to solder wires on circuit boards:

Invest in a quality soldering station with adjustable temperature control for easy learning. Cheap irons make it more complicated.
Use leaded solder initially – it has a lower melting point than lead-free, so it flows easier when starting.
Keep hands steady by resting palms on the work surface. Use a helping hand clip stand to free up both hands.
Buy various tip styles and sizes to handle joint types and pin configurations.
Apply enough solder to form a concave fillet – excess convex solder can cause bridges.
Position the circuit board horizontally to prevent solder rolls from falling onto the work area—tilt the board to aid solder flow.
Use adequate lighting or magnification to see the board and joint. Avoid soldering in shadows.
Have copper braid and a solder sucker ready to remove excess solder and correct bridged joints.
Purchase a practice soldering project kit online to gain experience without risking actual circuits.
Watch tutorial videos to learn proper soldering techniques before attempting it yourself.
Take an introductory soldering class for hands-on practice at a local maker space or community college.
Find an experienced soldering mentor who can observe your technique and offer correction tips.
Be patient with yourself, as soldering is a skill that takes time and repetition to master. Expect a learning curve.
Follow assembly instructions carefully and double-check all connections before powering up circuits.

With the right tools, learning aids, mindset, and techniques, new soldiers can steadily gain expertise through deliberate practice.

Advanced Techniques for Smooth Soldering

Use soldering iron tips matching the pad size and component lead. More extensive tips can transfer heat faster for bigger joints, while smaller tips are better for precision work. Select conical, chisel, or screwdriver-style tips shaped for the joint.
Keep the soldering iron tip properly tinned by regularly applying a small amount of solder. This ensures the heat transfers quickly to the joint. Retin the tip before each solder joint.
Use adhesive-backed heat sinks stuck to nearby temperature-sensitive components. The heat sink draws heat away and prevents damage. Use graspers to hold heat sinks in place.
For large copper fill areas or ground plane pads, preheat the entire section gradually before soldering to prevent cracks or lifts in the copper. Apply heat in a circular motion.
Soldering boards with multiple components, solder progressively in sections to avoid localized overheating. Solder all through-hole components first before moving to surface mounts.
Feed solder wire to the joint, not directly onto the iron tip. This gives better control of solder flow. Applying solder to the hot iron can lead to excess.
Use one hand to steadily hold and position the soldering iron and the other to feed the solder and inspect joints. This two-handed technique gives the best results.
Inspect all solder joints under magnification after cooling to check for defects like cracks, holes, or shorts. Use an inspection microscope or magnifying glass.
Clean flux residues after soldering using isopropyl alcohol and toothbrushes. The remaining active flux can corrode copper over time. Rinse cleaned boards with water.
Apply acrylic conformal coating using a brush or spray for boards prone to moisture damage. This creates a protective barrier against corrosion and leakage.

Soldering well requires patience and strict adherence to procedures. Follow datasheet guidance for soldering temperatures and times to avoid component damage. Taking the time to solder correctly prevents rework.

Troubleshooting Common Soldering Problems

Here are solutions to some typical problems faced when soldering wires on circuit boards:

Cold Solder Joints

If reheating the joint doesn’t help, apply fresh flux to remove surface oxides before reapplying the solder.
Use solder wire with a flux core to ensure the flux is active and not dried out. Old flux can cause poor solder flow.
Increase soldering iron temperature slightly above the normal range for the solder alloy. This provides extra heat to form the joint.
For troublesome joints, try a sustained contact preheat of the pad for 2-3 seconds before flowing solder.

Dry Joints

Apply a small amount of liquid flux on the surfaces using a brush before soldering to remove oxides.
Make sure pad surfaces are clean. Scrub off any grease, oil, or coating if present using isopropanol.
Try a higher soldering temperature and use the correct tip size to deliver sufficient heat to the joint.
If issues persist, consider tinning the surfaces before attempting to solder them together.

Bridging

Control solder flow by cleaning the soldering iron tip, using minimal solder quantity, and angling the tip.
Use a desoldering braid to absorb excess solder between pads. Be careful not to damage pads.
Remove the bridged component and adjust pad spacing before resoldering the component correctly for severe cases.

Solder Balls

Wipe the iron tip on a wet sponge frequently while soldering to clear any residual solder.
Twist or lightly tap the iron tip on the sponge to remove stubborn solder blobs sticking to it.
Hold the board horizontally or tilted downwards to prevent solder ball drips from falling onto the work area.

Oxidized Pads

Use a stiff wire brush to gently scrub away oxidation from pads without damaging the underlying copper.
For corroded pads, scrape gently with a knife to reveal fresh metal before soldering.
If a pad is damaged beyond repair, run a jumper wire to an alternate nearby pad to salvage the circuit.

Proper soldering practices and debugging techniques can help overcome many common issues.

Safety Tips for Soldering Wires on Boards

Soldering can cause harm if not done carefully. Follow these essential safety measures:

Work in a well-ventilated area to disperse fumes – use a fume extractor if possible.
Wear ANSI-approved safety glasses to prevent eye injuries from hot solder or sparks.
Tie back long hair and avoid wearing hanging jewelry when soldering.
Wear latex gloves to protect hands – solder can cause burns on contact.
Handle hot soldering irons safely – place on stands when not in use.
Unplug irons when idle for long periods to avoid accidental tipping over.
Keep a fire extinguisher and first-aid kit handy in the soldering area.
Moisten sponges for cleaning tips – dry sponges can be fire hazards.
Avoid eating or drinking when soldering to prevent ingesting contaminants.
Wash hands thoroughly with soap and water after finishing soldering.
Store solders and chemicals safely out of reach of children and pets.

Make safety an utmost priority. Stop soldering if you feel unwell from exposure to fumes. With caution, soldering can be conducted risk-free.

Conclusion

Learning how to solder wires properly on a circuit board is an essential electronics skill. With some basic tools, equipment, and supplies, a well-prepared workspace, and following systematic soldering techniques, you can quickly master soldering wires for prototyping or repairing boards. Start by practicing on scrap materials, learn how to troubleshoot poor joints, use safe practices, and progress to more complex soldering tasks. Soldering takes a steady hand, patience, and lots of practice to perfect.

Frequently Asked Questions (FAQs)

What is the best solder type for wiring circuit boards?

For most electronics work, rosin-core 60/40 tin/lead or 63/37 tin/lead solder with a diameter of 0.5 mm to 1 mm is ideal. Lead-free solders like SAC 305 (96.5Sn/3Ag/0.5Cu) can also be used.

What is the right soldering iron temperature for wires?

A tip temperature of 330°C to 380°C works for soldering wires on circuit boards. Higher temperatures may be needed for larger wires or ground planes. Start low and increase slowly till the solder flows well.

How much solder should be used on a wire joint?

Use just enough solder to cover the pad and wire. 1mm to 2mm of solder fillet is usually sufficient. Too little solder can cause dry joints, while excess solder increases the chances of bridging.

Can stranded wires be soldered on PCBs?

Yes, stranded wires can be soldered effectively by tinning the strands together before soldering to the board pad as a single strand. Bend strands to improve mechanical strength.

Is flux necessary for soldering wires to circuit boards?

Flux is highly recommended as it cleans surface oxides, improves solder flow, and prevents re-oxidation during soldering. For occasional soldering, rosin-core solder contains enough flux.

How long should pads be heated before applying solder?

Heat pads for 1 to 3 seconds before applying solder for small joints. Heating for longer risks pad damage. For larger pads and ground planes, preheat for 4-5 seconds.

Experience exceptional PCB manufacturing and assembly services with MorePCB!

Let us be your trusted partner for high-quality PCB solutions!

Tag: PCB Assembly