Thin laptops increasingly use BIOS chips in WSON-8 packages: small flat rectangles with contacts underneath instead of legs at the sides. The standard SOIC-8 test clip cannot grip them, so the familiar "clip and read" routine does not work. There are three practical ways to read and program a WSON chip: a spring-pin probe pressed onto the contacts, removing the chip and putting it in a socket, or soldering wires. This guide explains each, with the precautions that keep the chip and the board safe.
What a WSON-8 package is
WSON (and the similar USON) is a leadless package with eight small contacts along two edges and, usually, a larger exposed pad in the middle of the underside. Common body sizes are around 6 × 5 mm and 8 × 6 mm. The contacts are flush with the package edge, so there is nothing for a clip to hold. The package type is described under wson.
The pinout is the same as the SOIC-8 version of the chip: chip select, data out, write protect, ground, data in, clock, hold/reset and supply. Pin 1 is marked with a dot or a corner mark on the top.
Option 1: spring-pin probe on the board
A WSON probe is a small fixture with eight spring-loaded pins arranged to match the contacts. You press it onto the chip in place and hold it while the programmer reads or writes.
Advantages:
- no soldering, no heat on the chip;
- quick to try.
Limitations:
- you must hold it steady for the whole operation;
- the contacts must be exposed enough at the edges for the pins to reach them;
- in-circuit reading has the same problem as with a clip: the programmer may power other parts of the board through the chip's supply, which can make the read unreliable.
Read twice and compare; if the reads differ, the contact is not reliable.
Option 2: remove the chip and use a socket
Removing the chip and placing it in a WSON socket gives the most reliable reads and writes:
- Apply flux around the chip.
- Shield nearby parts with tape.
- Heat the chip evenly with hot air until the contacts and the exposed pad release; the exposed pad needs more heat than the edge contacts.
- Lift it straight up with tweezers when everything is molten.
- Clean the chip's contacts and pad with wick so it sits flat in the socket.
- Put it in the socket adapter, oriented by pin 1, and read.
The socket connects the chip to the programmer like a normal SOIC adapter. Programmer basics are covered in How to Read and Write a BIOS Chip with a CH341A Programmer; hot air technique in Hot Air Station Basics for Laptop Repair.
Refitting the chip
- Tin the board's pads thinly and level them with wick, leaving a small amount of solder.
- Apply fresh flux.
- Place the chip with pin 1 in the right corner and align it carefully.
- Heat until the chip settles into place on its own — surface tension centres it.
- Check under the microscope that every contact is wetted and there are no bridges.
The exposed pad is important: on many chips it connects to ground or should be soldered for mechanical stability. Too much solder under it, however, can lift the chip and leave edge contacts open. A thin, even layer works best.
Option 3: soldered wires
Fine wires soldered to each contact's edge can connect the chip to a programmer without removing it. It is fiddly and only practical with a good microscope and fine wire, but useful when the chip must stay in place and no probe fits. Keep wires short, and remove every trace of them afterwards.
Voltage
Many WSON chips on recent boards are 1.8 V parts. Check the part number before connecting anything; a standard CH341A drives 3.3 V. Use a 1.8 V adapter when needed, as explained in CH341A 1.8V Adapter: When You Need It.
Programming a new chip before fitting
When a WSON chip is damaged and must be replaced, program the new one in the socket before soldering it to the board. Writing and verifying it off the board avoids in-circuit power problems entirely, and you solder the chip only once. Keep the old chip as well, if it can still be read: it may hold the board's unique data.
Choosing a method
| Situation | Best option |
|---|---|
| Quick read for diagnosis, chip accessible | Spring-pin probe |
| Reads unreliable in circuit | Remove and use a socket |
| Writing a recovered image | Socket, for a reliable write and verify |
| Chip under a shield or close to tall parts | Remove, or soldered wires |
When comparing clip-style access with removal for SOIC chips, the same reasoning applies; see SOIC8 Clip vs Desoldering: Safe BIOS Chip Programming.
Tools that make WSON work easier
- A WSON spring-pin probe in the body size your boards use; check both common sizes.
- A WSON socket adapter that plugs into the programmer like a SOIC adapter.
- Fine tweezers with flat, parallel tips for lifting and placing the chip.
- Good flux and fine solder wick for cleaning pads.
- A microscope for alignment and checking every contact after refitting.
Protecting the pads
WSON pads on the board are small and the exposed pad is connected to a large copper area, which makes it slow to heat. That combination is how pads get lifted: the edge contacts melt first, the centre pad does not, and the chip is pulled too early. To avoid it:
- preheat the board or warm the area gently first;
- use enough flux under the chip edges so it reaches the exposed pad;
- nudge the chip sideways gently before lifting — it moves freely only when the centre pad is molten;
- never lever the chip up.
Verification
Whatever method you use:
- read twice and compare checksums before trusting a read;
- after writing, verify the chip's content against the file;
- if the chip was removed, read it once more in the socket after writing, before refitting.
Example: a probe that would not read reliably
A thin laptop's WSON chip gives a different checksum on every read with a spring-pin probe. The board's always-on circuitry is drawing power through the chip's supply pin, and the probe's contact varies slightly as it is held. The chip is removed with hot air and flux, cleaned and placed in a socket. Two reads now match. A corrected image is written and verified in the socket, the board's pads are levelled, and the chip is refitted with a thin layer of solder under its exposed pad. The board starts on the first try.
FAQ
Can I use a SOIC-8 clip on a WSON chip?
No. There are no legs for the clip to grip. Use a probe, a socket or wires.
Is it risky to remove a WSON chip?
With flux, shielding and controlled heat it is routine. The exposed pad needs more heat than the edges; do not pull before it releases.
Does the exposed pad need solder?
On most chips, yes — for ground and mechanical stability. Use a thin, even layer.
Why do in-circuit reads differ?
The programmer may power other parts of the board, and the probe contact can vary. Remove the chip for reliable results.
Are WSON chips always 1.8 V?
No, but many on recent boards are. Check the part number.
Bottom line
WSON chips cannot be clipped. Use a spring-pin probe for quick reads, remove the chip and use a socket for reliable reads and writes, and refit it with flux, alignment and a thin layer of solder under the pad. Check the voltage first, read twice and verify every write.