Basic soldering techniques

Steps in proper soldering

1. Clean all solder pads and device terminals for good wetting.

2. Clean soldering iron/gun and wait until proper operating temperature is reached, otherwise components will heat up excessively.

3. Mount devices on the board properly.

? Elevate components from board surface (few mm.) to prevent heating of circuit board.

? Mount components exactly parallel to board surface if using horizontal mounting, or exactly perpendicular to it if using vertical mounting.

? Cut excess leads after device insertion leaving only a length equal to radius of pad.

? Use plastic mounting clips/holders for large devices to reduce mounting stresses.

4. Heat sink the leads of sensitive devices to prevent heat damage.

5. Apply soldering iron/gun to both terminal lead and copper pad to equally heat both.

6. Apply solder to both lead and pad but never directly to the iron/gun. Direct contact will cause the molten solder to flow over the gun and not over the joint.

7. The moment the solder melts and begins to flow, remove the solder supply immediately. Do not remove the iron yet. The remaining solder will then flow over the junction of the lead and pad, assuming both are free of dirt.

8. Let the iron heat the molten solder for a few seconds. This will let the excess flux vaporize.

9. Remove the iron from the junction and let the junction cool.

10. DO NOT MOVE THE JOINT WHILE IT IS COOLING. Doing so will result in a fractured joint.

11. Do not blow air onto the joint while it is cooling. Instead, let it cool naturally.

? A good solder joint is smooth and shiny. The lead outline should be clearly visible.

12. Clean the soldering iron tip before you begin on a new joint. It is absolutely important that the iron tip be free of residual flux and solder.

13. After you finish all of the joints, remove excess flux residue from the board using alcohol, acetone, or other organic solvent.

Common mistakes

? Solder peaking - solder forms peaks as you remove iron from joint which is not hot enough. Correct this by re-heating the joint.

? Incomplete wetting - solder does not bond with the copper surface or component lead. The surfaces may not be clean enough or insufficient heating of joint. Correct by reheating or by cleaning surfaces before re-soldering.

? Excessive solder - solder has convex surface and lead outline not plainly visible. Remove excess solder.

? Cold solder - solder did not fully bond with either the pad or the lead. This is caused by inadequate heating or by poor cleaning of surfaces. The solder forms puddles or clusters and is dull gray in appearance. Clean surfaces and re-heat to correct this.

? Rosin joint - flux not fully evaporated, forms insulating layer under joint surface. Reheat joint.

? Fractured joint - joint was moved during cooling, has cracked appearance. Re-heat joint and cool without moving it.

? Porous joint - flux forms trapped gases due to insufficient heating time, pinholes visible in joint. Re-heat joint.

? When soldering, check for continuity between device leads and solder, between solder and wire or pad, and between all device leads joined by the solder. Check for cold, fractured, or incomplete solders which may cause the joint to be unreliable. Check for excessive solders and peaking which can lead to short circuits between adjacent joints. Also, avoid excessive heating which can burn pads off the circuit board or melt the device being soldered.