Two-iron removal of a 0805 chip
Two irons remove a passive in two seconds without touching the body, which matters when the part is under a microscope and the neighbouring components are 0.5 mm away. The technique is also the safest way to lift a component from a board you intend to re-use.
Procedure
- 1
Flux both joints with ROL0 so the alloy reflows at the lowest possible temperature.
- 2
Approach along the long axis of the component with both knife tips at 330 degrees C, one tip per termination.
- 3
Hold both tips in contact for 1.5 seconds until both fillets visibly go liquid.
- 4
Lift the first iron 0.5 mm, then the second, letting the part tilt off the pads.
- 5
Catch the component with tweezers on the body edges and inspect both pads for remaining solder before re-placing.
Workshop notes
Bring both tips in from opposite sides
Approach along the long axis of the component, not across it. Each knife tip contacts one termination and its pad, so heat goes into both joints simultaneously. Coming in across the body means one tip has to span the ceramic, which is a thermal insulator and will not conduct heat to the far joint.
Why a knife and not a chisel
A 2.0 mm knife presents a narrow edge that fits between the termination and the neighbouring parts on 0.8 mm pitch placements, while its flat face still gives a 1.5 mm contact length along the pad. A chisel of the same width has its widest dimension across the joint and will foul the adjacent component. Keep the knife edge parallel to the joint, not perpendicular to it.
The lift, and why it is a rotation
When both joints are liquid - typically 1.5 seconds at 330 degrees C - lift one iron by 0.5 mm first, then the other. The part tilts and comes away with both terminations still tinned, ready to be placed again. Pulling straight up with both irons at once usually flicks the part into the bench. Tweezers can help, but grip the body edges, never the terminations.
Practice drill
Remove and replace the same 0805 ten times, checking after each cycle that both terminations are still fully tinned and that no pad has been lifted. Most operators destroy a pad on the third or fourth cycle if they are holding too long; the drill teaches you what two seconds actually feels like.
Failure modes
| Symptom | Cause | Treatment |
|---|---|---|
| Part flies off the board when lifted | Both irons lifted simultaneously, and the residual flux vapour ejected the part | Lift one iron half a millimetre before the other so the part tilts off, and keep tweezers ready at the body edges |
| One joint stays solid and the pad lifts | Tips approached across the body, so the ceramic insulated the far joint | Re-approach along the long axis, add flux, and give both joints a two-second pre-heat before attempting the lift |
| Termination partially de-tinned after removal | Alloy stayed with the pad because the part was lifted while the joint was still pasty | Wait for both fillets to visibly go liquid and glossy before lifting, and pre-tin the pads lightly rather than heavily |
Supplies
- ROL0 no-clean flux pen
- 0.5 mm SAC305 wire for re-tinning pads if needed
- 1.5 mm desoldering braid
- Isopropyl alcohol and swabs
Tools
- Two soldering stations, both at 330 degrees C
- 2.0 mm knife tips on both
- Fine tweezers
- 10x stereo microscope
Safety
Two irons means two hot faces moving in a small space and a real risk of crossing your own hands. Set both stations to sleep between parts, and keep the second iron parked in a stand rather than loose on the mat.
Neighbouring cards
- Drag soldering a SOIC-8 with gel flux 340 °C / 1.5 s
- Hand-placing a 0402 passive 320 °C / 1.0 s
- Dragging a 0.5 mm pitch QFP and clearing bridges 350 °C / 1.2 s
- Fixing tombstoned 0603 and 0805 parts 310 °C / 1.0 s