How to Cut and Solder COB LED Strips: A Field Guide for Installers

COB strip looks fantastic — a continuous line of light with no dots — but it's less forgiving than SMD when it comes to cutting and soldering. The contact areas are smaller, the board runs hotter during a joint, and one heavy-handed move can kill a section. I've ruined enough offcuts to know the pitfalls. Here's the field procedure I use on installs.

Cutting: only on the marks

COB strip has cut points printed at regular intervals (commonly every ~50mm on 24V, sometimes closer on free-cut versions). The mark usually looks like a line with a small pad on either side.

1. Measure twice — once you cut COB you can't join it invisibly without a connector or solder joint.
2. Cut dead straight across the marked line with sharp scissors or a craft knife against a straight edge.
3. If your strip is "free-cut" (cut anywhere), you still cut perpendicular and clean; the continuous phosphor means there's no fixed point.

Waterproof COB has a silicone sleeve — peel it back from the contact area before you cut to length or solder, then reseal with silicone or heat-shrink after.

Soldering COB: lighter and faster than SMD

The copper pads on COB are small and sit right next to the phosphor/die layer, so heat travels fast and can damage the emitters. Adjust your technique:

• Run the iron a touch cooler than SMD — around 300–320°C — and get in and out quickly.
• Use plenty of flux; the pads are tiny and good flux is what gets solder to wet them.
• Tin the pad with a minimal dome — big blobs bridge the narrow gaps.
• Use fine, pre-tinned wire (20–22AWG for feed runs). Hold it to the pad and touch both with the iron for one to two seconds until they merge, then hold still while cooling.
• Keep the joint under about three seconds of heat. If it's not wetting, remove, re-flux, and retry rather than cooking the board.

Using connectors instead

For COB I often use purpose-made COB solderless connectors on accessible joins — they're designed for the continuous pad layout and save you from tiny solder joints in awkward spaces. They must be the exact width and type for your COB model. For permanent or high-current feed points I still solder; the general connector family is in the connector guide, and the broader SMD soldering method (temperatures, tinning) is in the soldering tutorial.

Mistakes that ruin a COB strip

• Iron too hot or held too long — discolors the phosphor and kills nearby emitters.
• Not enough flux — cold, grainy joints on the tiny pads.
• Solder bridging across the narrow pad gaps — causes a short.
• Cutting off the mark on fixed-cut strip — leaves a section with no usable contacts.
• Forgetting to reseal waterproof COB after soldering.

FAQ

Can I cut COB strip anywhere?

Only on "free-cut" versions. Standard COB must be cut at the printed marks or the section won't have contacts and a short length may not light.

Why did the LEDs near my solder joint turn dim or change color?

Heat damage from an iron that was too hot or held on too long. Work cooler, faster, with more flux, and practice on an offcut first.

Is it better to solder or use a connector on COB?

Connectors for accessible, possibly-serviced joins; solder for permanent feed points and high-current runs. Many installs use both — connectors at corners, solder at the driver end.

If you tell me the COB model and run length I'll confirm the cut interval, connector type, and wire gauge — start from the COB strip range and I'll match the accessories.