HOW-TO GUIDE
How to Solder a Replacement Microphone Onto a Circuit Board
By the OhmSavvy Research Team ·
Safety and static before you start
- Disconnect the battery or unplug the device. Phones and laptops keep battery power on the board even when switched off.
- Electret capsules contain a JFET and MEMS microphones contain an amplifier chip; both are static sensitive. Work on an antistatic mat, wear a grounded wrist strap if you have one, and use a grounded iron.
- The tip runs at around 300 °C or more. Use a fume extractor or fan, wear eye protection, and wash your hands after handling leaded solder.
Which replacement microphone do you have?
Three kinds turn up in repairs, and they need different handling. Read the old part before ordering a new one: diameter, height, pin count and whether it has leads, pads or a flex.
| Type | How it connects | Ground pin | Solder with |
|---|---|---|---|
| 2-pin electret capsule | Two leads or two rear pads | Joined to the metal case | Iron |
| 3-pin electret capsule | Source, drain and case pads | Case pin; source may be separate | Iron |
| Electret with wire tails | Pre-soldered leads to a connector or pads | Usually the black or shield wire | Iron |
| MEMS microphone (SMD) | Pads under the package, sound port through the board | One of the bottom pads | Hot air, sometimes a preheater |
1Find the polarity and the ground pin
An electret capsule is polarised. Inside it, a JFET buffers the tiny signal from the charged diaphragm, and the case is part of the ground return as well as the shield. On a 2-pin capsule the ground pad normally has one or more copper traces running from it to the rim of the metal can, which you can often see by eye. When you can't, a continuity check settles it: one probe on the case, the other on each pad in turn. The pad that beeps is ground.
On the board, the ground pad usually joins a large copper area or the ground side of nearby decoupling capacitors, while the signal pad goes to a bias resistor and a coupling capacitor. Our guide to using a multimeter covers continuity mode if you haven't used it before. Photograph or mark the board before the old capsule comes off, so you have a record of which way round it sat.
2Remove the old microphone
Add fresh flux and a little new solder to each joint; old, oxidised joints melt more readily once diluted. On a leaded capsule, heat one pin while drawing it out a little, then the other, rocking gently. A capsule with rear pads lying flat on the board is easier to lift once both pads are molten together, so flood both with solder and use a wide tip across them, or clear each with wick first. If the old microphone is the fault, it does not matter if it gets hot, but the board pads do: never lever on a pad that is still solid.
3Prepare the leads and pads
Wick the board pads flat and clean. If the replacement capsule has bare pads and the original had leads, solder short lengths of tinned copper wire to the capsule first, working quickly. Pre-tin everything: the capsule pads, the wire ends and the board pads. Pre-tinned surfaces join in a second or two, which is the point of the whole exercise, because the joint itself then needs only a brief touch of the iron.
4Solder the replacement microphone with minimal heat
Heat is the main risk to the new part. The electret film holds a permanent charge that high temperatures can reduce, lowering sensitivity, and the plastic and felt parts inside soften easily. Keep each joint to a few seconds, solder one pad, let the capsule cool, then do the other.
- Clip a small heat sink or a pair of locking tweezers on the lead between the joint and the capsule.
- Keep the iron and solder away from the front face, the acoustic cloth and the sound hole.
- Use a clean chisel or bevel tip that carries heat well, so contact time stays short.
- Keep flux away from the sound port; it can wick inside and stiffen the diaphragm.
01
Identify GND
Continuity to the case
02
Pre-tin
Pads, leads, board
03
Pad 1
Heat sink on, 2–3 s
04
Cool
Let the can return to room temp
05
Pad 2
Same, then inspect
For tip shapes that move heat quickly, see soldering iron tip types. If you are new to making joints, the basics in how to use a soldering iron apply here too.
Lead length and shielded cable
A microphone signal is only millivolts, so every centimeter of unshielded wire acts as an aerial for mains hum and digital noise. Mount the capsule as close to the board as the enclosure allows. Where it has to sit remotely, as in a headset boom, a camera housing or a dashboard, use thin shielded audio cable: center conductor to the output pad, braid or drain wire to the ground pad. Ground the shield at the board end, keep the exposed pigtail short, and slide heat-shrink over the capsule joints so the shield cannot short the output.
MEMS microphones in phones and laptops
Phones, laptops, earbuds and smart speakers mostly use MEMS microphones: tiny rectangular SMD packages, typically a few millimeters across, with land pads underneath and a sound port that lines up with a hole drilled through the board (bottom-port) or sits on the lid (top-port). A hand iron is not suitable when the pads are hidden under the body, which is nearly always. Hot air, with the board preheated and the area around shielded with Kapton tape, is the usual method.
Protect the sound port
Many devices also place the microphone on a small daughterboard or the charging-port flex. If yours does, replacing that module is a connector swap rather than micro-soldering.
5Test the new microphone
With the device powered, measure DC voltage between the microphone's output pad and ground. An electret biased through a resistor normally sits somewhere between ground and the supply, often around half of it; the exact figure depends on the capsule and the resistor. Near 0 V suggests a short or reversed part, and the full supply voltage suggests the JFET is open or a joint failed.
Then do a real-world check: make a voice recording or a call and listen back for level, hiss and hum. Low or crackling audio that comes and goes points to a dull joint; see fixing a cold solder joint.
Irons and hot air for microphone replacement
A temperature-controlled iron covers electret capsules; MEMS parts call for hot air. Compare more options in our best soldering iron for circuit board repair guide.
Tools in our reviews
85W digital station (70W iron) with an ESD-safe design that protects sensitive components.
Soldering iron and hot air gun in one station, for SMD rework.
USB-C PD powered with an OLED display, for portable and field repairs.
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Frequently asked questions
Does it matter which way round an electret microphone goes?
Yes. The capsule contains a small JFET that needs its drain at the positive bias and its source and case at ground. Reversed, it will usually produce no sound or a very weak, distorted signal, and the metal case ends up at signal potential, so it picks up hum. Reversing it briefly at low bias voltages rarely destroys it, but check the ground pin before soldering.
Can I replace a 3-pin electret microphone with a 2-pin one?
Often, yes. In a 3-pin capsule the source and drain are separate, while in a 2-pin capsule the source is tied internally to the case. If the circuit grounds the source pin, a 2-pin part with its case pin to ground and output pin to the drain connection usually works. Check the original circuit before assuming, because some designs use the source pin as the output.
What temperature should I use to solder a microphone?
With leaded solder, a setpoint around 300 to 330 °C is a common choice, and lead-free typically needs a little more. A hotter tip lets you finish each joint sooner, which matters more than the setpoint itself. Keep contact to a few seconds per pad, and check the capsule datasheet if it lists a soldering heat limit.
Why does my new microphone hum or buzz?
Hum usually means the case or cable shield is not properly grounded, the capsule is reversed, or a long unshielded lead is picking up interference. Check continuity from the case to board ground, confirm the signal wire goes to the bias resistor side, and replace long loose wires with shielded cable that has its braid grounded at the board end.
Can I replace a phone microphone with a soldering iron?
Rarely. Most phone and laptop microphones are MEMS parts whose pads sit underneath the package, out of reach of an iron tip. They are normally removed and fitted with hot air, often with board preheating. Some phones put the microphone on a replaceable flex or charging-port board, in which case swapping that board is far easier than soldering the part.
