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October 14, 2009

What is a Disturbed Solder Connection?

Can you offer a clear description of what you call a disturbed solder connection?

I'm having quite a disagreement with my engineers on what is and what isn't a disturbed connection.



J. S.

Experts Comments

What is a disturbed solder joint? This is a interesting and difficult question to answer. There are many terms and examples that have been used. Let's look at what a disturbed solder joint is not first.

Is it similar to a grainy solder joint? No, not usually, How about a shinny verse a not shinny solder joint or a tarnished solder joint? No, it's not like those types of terms either.

To simplify, the formation of a disturbed solder joint happens during the solidification process of the alloy. Meaning, during the cooling process. When alloys are in their molten state their surface appearance can be effected by outside mechanical influences while passing into the solidification point of the alloy being used.

What do they look like? They usually have a formation in the joint that looks like a ripple or a type of pattern in the solder joint surface. These are easily observed and often seen in a through hole soldering process but are more difficult to determine in an SMT process. However, they can still exist in this process too.

What are the major points that can cause this? Let's consider your defect description as one you are seeing in a through hole soldering process such as wave soldering as it's most common in this process.

Major contributors to the formation of a disturbed solder joint in this process is usually due to some outside vibration of the assembly during the cooling process. This can come in the form of a jerky finger conveyor, a high vibration coming from the exhaust systems attached to the soldering system performing the soldering task.

A simple test would be to place a clear glass of IPA on your conveyors. If you have considerable vibrations they will show up visually in the IPA usually.

If you see this, you can begin to systematically turn on and off sub-systems,conveyors and exhaust units to help determine the location of the root cause.

Another contributor can be easily caused by operators. Reaching into a system and removing an assembly prior to the solder joints ability to solidify, or the PCB transferring from one conveyor to another while the alloy remains in the liquid state.

It is the movement of the assembly while the alloy is in the liquid state that creates a disturbed solder joint. The above is operator influence is less likely to happen in a lead free environment due to the alloys ability to solidify rapidly.

Additionally, be careful of the use of high impact fans blowing on the solder joint during the cooling process of the joints.

John Norton
Eastern Manager
Vitronics Soltec
John Norton started his soldering career in 1983 for Hollis Engineering. He has also worked with Electrovert as a technical training manager and Vitronics Soltec for the last ten years. He has held various technical development and sales positions.
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