How To Repair A Bad Solder Joint

The Platonic Solder Joint

The ideal solder articulation for through-pigsty components should resemble the diagram beneath.

The photos that follow show some mutual soldering problems, with suggestions for repair and prevention:

Disturbed Joint

A Disturbed joint is one that has been subjected to movement every bit the solder was solidifying. The surface of the articulation may appear frosted, crystalline or rough.

Often chosen a 'Cold Articulation'. They can look like to a true cold joint, only the cause is dissimilar.

Repair: This articulation tin can be repaired by reheating and allowing it to cool undisturbed.

Prevention: Proper preparation, including immobilizing the joint and stabilizing the work in a vise can forbid disturbed joints.

Cold Joint

A 'Cold Joint' is one where the solder did not cook completely. It is oft characterized by a rough or lumpy surface. Common cold joints are unreliable. The solder bond will exist poor and the cracks may develop in the articulation over time.

Repair: Cold joints can normally be repaired by simply re-heating the joint with a hot atomic number 26 until the solder flows. Many cold joints (such equally the one pictured) also suffer from as well much solder. The excess solder tin can ordinarily be drawn-off with the tip of the iron.

Prevention:

A properly pre-heated soldering iron with sufficient power volition help prevent cold joints.

Overheated Joint

At the other extreme, we accept the overheated joint. The solder has not even so flowed well and the residuum of burnt flux will make fixing this joint hard.

Repair: An overheated articulation tin usually be repaired afterward cleaning. Careful scraping with the tip of a pocketknife, or fiddling isopropyl booze & a toothbrush will remove the burnt flux.

Prevention: A clean, hot soldering iron, proper preparation and cleaning of the joint will help preclude overheated joints.

Insufficient Wetting (Pad)

These two joints both show signs of insufficient wetting of the solder pad. The solder has wetted the leads nicely, only it has non formed a good bond with the pad. This can exist caused past a dirty circuit board, or by failing to use estrus to the pad every bit well as the pivot.

Repair: This condition can usually be repaired by placing the tip of the hot fe at the base of the joint until the solder flows to cover the pad.

Prevention: Cleaning the board and fifty-fifty heating of both the pad and the pin will prevent this trouble.

Insufficient Wetting (Pin)

This solder in this joint has non wetted the pin at all and has only partially wetted the pad. In this case, estrus was non applied to the pin and the solder was not given adequate time to flow.

Repair: This joint can be repaired past re-heating and applying more solder. Exist sure that the tip of the hot fe is touching both the pin and the pad.

Prevention: Even heating of both the pin and the pad will prevent this problem.

Insufficient Wetting

(Surface Mount)

Here we have 3 pins of a surface mount component where the solder has non flowed onto the solder pad. This is caused by heating the pivot instead of the pad.

Repair: This is hands repaired by heating the solder pad with the tip of the iron, then applying solder until information technology flows and melts together with the solder already on the pin.

Prevention: Heat the pad first.

Solder Starved

A solder starved joint just does not have enough solder. Information technology may make good electrical contact, but it is difficult to verify by inspection. In any instance, it is not a potent articulation and may develop stress cracks and neglect over fourth dimension.

Repair: Re-heat the joint and add together more solder to make a good strong articulation.

Too Much Solder

This might exist a perfectly adept joint, only we can't tell for sure. It is entirely possible that this blob of solder wets neither the pin nor the pad and is not a reliable electrical connection. The best evidence of proper wetting (and good electrical contact) is a dainty concave surface as on the joint on the far left.

Repair: Information technology is usually possible to draw off some of the backlog solder with the tip of a hot iron. In extreme cases, a solder-sucker or some solder wick can exist helpful besides.

Untrimmed Leads

Leads that are too long are potential short circuits. The two joints on the left are an obvious danger of touching. But the one on the right is long enough to exist dangerous as well. Information technology would not accept much forcefulness to bend that lead over to touch an adjacent trace.

Repair: Trim all leads only at the top of the solder joint.

Solder Span

The left two solder joints have melted together, forming an unintended connexion between the two.

Repair: Sometimes the backlog solder can exist fatigued off by dragging the tip of a hot iron between the two solder joints. If there is too much solder, a solder sucker or solder wick tin can help get rid of the backlog.

Prevention: Solder bridges most often happen between joints with likewise much solder to begin with. Use only enough solder to make a good joint.

Lifted Pad

This photo shows a solder pad that has become detached from the surface of the circuit board. This most oftentimes occurs when trying to de-solder components from the board. Only it tin can result simply from overworking the joint to the point where the agglutinative bond between copper and the lath is destroyed.

Lifted pads are especially common on boards with sparse copper layers and/or no through-plating on the holes.

Repairing a Lifted Pad

Information technology may not be pretty, just a lifted pad can usually be repaired. The simplest repair is to fold the lead over to a still-attached copper trace and solder it as shown to the left. If your board has a solder-mask, y'all will demand to carefully scrape off enough to expose the blank copper.

Other alternatives are to follow the trace to the next via and run a jumper to there. Or, in the worst instance, follow the trace to the nearest component and solder your jumper to the leg of that. Non exactly pretty, just functional.

Stray Solder Spatters

These bits of solder are held to the board only by gluey flux residue. If they work loose, they tin can easily crusade a brusk circuit on the board.

Repair: These are easy to remove with the tip of a knife or tweezers.

All of the Above!

Don't panic. Take your fourth dimension. Most joints can exist repaired with patience. If the solder refuses to flow the way you desire it to:

Stop and let the joint cool.
Clean and tin can your iron.
Clean off any burnt flux from the joint.
Permit the iron come up dorsum upwardly to temperature.
Then reheat the joint and try again.

Source: https://learn.adafruit.com/adafruit-guide-excellent-soldering/common-problems

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