Hand soldering is more forgiving than reflow in some ways and less in others: the iron can reach places the oven cannot, but the human hand needs room to work. Copper land (pad) widths designed for hand soldering must provide that room: enough exposed copper for the iron tip and the solder to form a proper fillet, without so much excess that solder bridges to neighbors or the joint becomes a heat sink that never reflows. Pad width is a clearance decision balancing solderability against density.
What the Iron Needs
A hand soldering iron tip must contact both the component lead and the pad simultaneously to heat the joint; solder then flows to the heat, forming the fillet. The pad must extend beyond the component body enough for the tip to land: a pad exactly the size of the lead gives the iron nowhere to sit except on the component itself, which heats the part instead of the joint. The extension, the pad area beyond the lead's footprint, is the iron's workspace.
For through-hole work, the annular ring provides this naturally if sized generously: a ring noticeably wider than the minimum for fabrication gives the iron a landing zone around the lead. For surface mount hand soldering, the pads should extend beyond the component's terminations by enough to place the iron tip, typically a fraction of a millimeter to a millimeter depending on the package size and the iron tip used.
Pad Width Rules by Package
The guiding principle scales with the package: the pad extends beyond the lead by roughly the width of the iron tip that will solder it, plus a margin. Small chip components (0402, 0603) soldered by hand want pads extended enough for a fine conical or chisel tip to contact pad and termination together; the extensions are small in absolute terms but large relative to the part. Larger packages (SOIC, through-hole) want correspondingly larger extensions for the bigger tips their thermal mass demands.
Resist the temptation to use the manufacturer's minimum reflow-optimized footprints for hand assembly. Those footprints assume paste, stencil, and oven; the hand needs more copper. Design a hand-solder variant of the footprint with extended pads, or accept that the reflow footprint will be fiddly and slow to assemble by hand.
Clearance to Neighbors
Extended pads consume space, and the space comes from the clearance to adjacent pads and components. The minimum pad-to-pad spacing must still prevent solder bridging: with hand soldering's less controlled solder volume, the bridging risk is higher than with paste, so the clearances should be more generous, not less. Solder mask between pads is the primary bridge defense; ensure the mask web between extended pads meets the fabricator's minimum.
- Keep solder mask defined pads where bridging is a concern; the mask dams the solder.
- Allow extra clearance around pads that will see rework; desoldering needs even more room than soldering.
- Consider the iron's approach angle; pads blocked by tall neighbors are pads that cannot be soldered.
- Thermal relief on pads connected to planes; a pad that sinks heat faster than the iron supplies it never solders.
Thermal Design of the Pad
A pad connected to a large copper pour acts as a heat sink, wicking the iron's heat away faster than a small iron can replace it. Thermal relief spokes, the narrow copper connections between pad and pour, limit this wicking while maintaining electrical connection. For hand soldering, thermal relief is more important than for reflow, because the iron's power is limited and localized while the oven heats everything at once.
Balance the relief against current-carrying needs: power connections may need the thermal mass for electrical reasons, in which case plan for a larger iron or preheating rather than compromising the copper. The pad's thermal design should match the assembly method honestly.
Verifying With the Iron
The ultimate test of pad design is soldering the actual board with the actual iron. A well-designed pad wets quickly, forms a smooth concave fillet, and releases the iron cleanly; the joint looks bright and smooth. Pads that fight the iron, taking excessive time or forming blobby, grainy joints, need wider extensions, better thermal relief, or both.
Prototype the footprint before committing to a production run. A single test board soldered by hand reveals pad problems that no design rule check catches, because the DRC knows the geometry but not the iron. The hand is the final design reviewer.
Extend pads for the iron tip, keep clearances bridge-safe, relieve thermally, and prove it by soldering. Hand soldering clearances are ergonomic engineering: the pad is the interface between the human and the circuit, and it should fit the human.
Related Guides
- Solder Mask Dam Thickness to Prevent Bridging: Between two adjacent surface-mount pads, a thin wall of solder mask, the dam, keeps molten solder from flowing across the gap and shorting the pads
- Selective Solder Drag Speeds on Dual-In-Line Leads: Drag soldering a row of dual-in-line leads looks like a magic trick the first time you see it done well. A grooved tip carrying a small reservoir of
- Selective Solder Flux Wave Heights on Mixed Boards: Selective soldering solders through-hole components on a board that already carries surface-mount parts, using a small, precise solder wave instead
- Thermal Relief Spoke Sizing on Power Planes: Thermal reliefs are the compromise between two enemies: the soldering iron, which needs the joint hot, and the power plane, which wants to wick that