Dead-bug wiring a TSSOP
Dead-bug mounting - the package upside down with its leads in the air - is the standard way to prototype with a fine-pitch part that has no breakout board. Each lead gets a 0.1 mm wire, and the whole assembly is held by the first two wires you solder.
Procedure
- 1
Straighten all leads under 20x and bend them outward 15 degrees with a fine probe.
- 2
Glue the package body upside down to the carrier board with a drop of adhesive and let it cure fully.
- 3
Solder the two corner leads first with 0.1 mm wire, leaving 30 mm of slack as strain relief.
- 4
Flux each remaining lead individually with a 0.2 mm nozzle pen and solder with a 0.8-second dwell at 300 degrees C.
- 5
Route the wires to the header, verify continuity, and tug each wire at 20 g to check the joint.
Workshop notes
Prepare the package before anything else
Straighten every lead with a 0.15 mm blade under the microscope so all leads lie in one plane. Bend the leads outward by about 15 degrees with a fine probe. Then glue the package body down with a drop of cyanoacrylate or UV-cure adhesive, because a TSSOP in dead-bug orientation has no mechanical support at all and the first wire you solder will otherwise drag the part across the bench.
Wire gauge and the first two anchors
Use 0.1 mm enamelled copper wire - the kind sold for magnet winding - and strip the enamel with a hot 380 degrees C tip rather than abrasion, which would nick the conductor. Solder the two corner leads first, using them as the mechanical anchors; leave 30 mm of slack behind the package so the wire does not pull. Everything after that is supported by these two.
The 0.8-second dwell
A TSSOP lead at 0.65 mm pitch is roughly 0.15 mm wide and sits on a package that conducts heat away poorly. At 300 degrees C with a 0.2 mm conical tip, 0.8 seconds is enough to make a joint with 0.3 mm wire; past 1.5 seconds the lead lifts off the plastic. Flux each lead individually with a 0.2 mm nozzle pen, and never reflow a joint you have already made unless you add flux again.
Practice drill
Dead-bug an 8-pin TSSOP and wire all eight leads to a header, then check continuity and mechanical stability by tugging each wire with 20 g of force. Fewer than one broken joint out of eight is a good result for a first attempt.
Failure modes
| Symptom | Cause | Treatment |
|---|---|---|
| Lead lifts off the package body | Dwell over 1.5 seconds, or the wire pulled on the lead while the alloy was solidifying | Cap the dwell at 0.8 seconds, add the 30 mm strain relief loop before the joint is made, and never reflow without fresh flux |
| Enamel does not strip and the joint will not wet | Iron too cool, or the wire was abraded instead, leaving a bare but oxidised conductor | Use a dedicated 380 degrees C tip and hold the wire end in a bead of solder for one second, watching for the enamel to smoke and recede |
| Package shifted during wiring | Adhesive not fully cured before the first wire was soldered | Wait out the full cure time, and tack the body down with a second drop at a different corner |
Supplies
- 0.1 mm enamelled copper wire
- 0.3 mm SAC305 solder wire
- ROL0 no-clean flux pen with a 0.2 mm nozzle
- Cyanoacrylate or UV-cure adhesive
Tools
- Station at 300 degrees C
- 0.2 mm conical tip and a 380 degrees C tip for enamel stripping
- 20x stereo microscope
- Fine probe and 0.15 mm blade for lead forming
Safety
Cyanoacrylate adhesive bonds skin in seconds: keep a debonder on the bench, not in a drawer, and never wipe a spill with a cloth you are also holding. Enamelled wire ends are sharp - cut them into a bin, not toward yourself.
Neighbouring cards
- Tip tinning, storage and end-of-day care 300 °C / 0.5 s
- Fixing tombstoned 0603 and 0805 parts 310 °C / 1.0 s
- Hand-placing a 0402 passive 320 °C / 1.0 s
- Two-iron removal of a 0805 chip 330 °C / 1.5 s