The difference is where the solder sits
A chisel has a flat working face with a squared edge across its width. It puts a broad, even contact patch on the pad and stores a useful amount of heat — which is why it is the default for through-hole pins and ground pads.
A bevel is cut at an angle, so the face forms a small reservoir behind the edge. During a drag pass it carries a controlled bead of solder along the row and deposits it at each pad. A knife tip is a narrower relative of the bevel, used where the row is tighter still.
Because both can be ground on the same shank, the decision is almost never about the iron. It is about what the joint will tolerate.
Choose by pitch, then by pad width
| Pitch | Start with | Why |
|---|---|---|
| 0.8 mm and above | Chisel 1.2–2.4 mm | Broad contact, high stored heat, low bridging risk |
| 0.5–0.8 mm | Bevel or knife 1.0–1.6 mm | Reservoir feeds the row without flooding adjacent pads |
| Below 0.5 mm | Knife / micro conical, or a bent shank | Clearance becomes the constraint; drag only after a sample test |
The width rule follows the pad: a face wider than the pad bridges its neighbour. On a 0.65 mm pitch connector, a 2.4 mm chisel will wet two pads at once no matter how carefully it is handled.
The fillet test
Drag a candidate tip across a scrap board with the production flux and alloy, then look at the joint under a bench magnifier rather than a microscope. A bevel usually leaves a small, concave fillet with a visible meniscus on each pad. A chisel tends to leave a flatter deposit that is harder to judge by eye, and on fine pitch it is more likely to leave a bridge between two pads.
If incoming inspection in your plant is visual, that difference decides the geometry. A joint that cannot be checked without equipment will eventually be checked incorrectly.
When neither is right
Three cases move the problem out of hand-soldering geometry altogether:
- Large thermal mass — a harness lug or a busbar pulls heat away faster than a small chisel can replace it. Start from a wide blade or a slotted hot-bar thermode.
- No vertical clearance — a connector housing above a 0.3 mm pitch FPC pad needs a bent shank, not a different face.
- Heat-sensitive component — a sensor lead needs low mass and a contact time under three seconds, which points to a micro conical or a cartridge.
Our application guide groups the same six joints by these constraints. If yours is not among them, send a photograph of the pad and the iron model and we will shortlist published geometries with their dimensions.
