Selecting a Through-Hole Soldering System, Part 1

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While through-hole assembly is much less commonly done than it was in the early days, and far less common than SMT assembly, it is still a viable and important technique that requires an understanding of the various soldering systems available. This column will outline the available methods and provide a brief overview of their strengths and weaknesses.

Methods of Through-hole Soldering

With the exception of selective soldering, the type of soldering technique you select will be largely dependent on anticipated board throughput. The simpler, less expensive techniques will only work for the lowest volume.

The five methods are:

1. Manual

2. Dip

3. Drag

4. Wave

5. Selective

Manual

Manual soldering is done simply by holding a soldering iron in one hand and manually feeding solder from the other hand to the through-hole component. Solder usually incorporates a flux core, so pre-fluxing is necessary. Simple irons don’t provide much control on temperature, while others can provide variable temperature control to prevent under- and over-heating components. This method is very labor intensive, and thus is used only for very low volumes. Quality is dependent on the operator’s training, experience and skill. Training courses and standards are available for personnel to improve their quality level.

Pros: Very inexpensive; prices range from $50 for a basic iron to $2,000 for a high tech version with temperature controls

Cons: Labor intensive; quality dependent solely on operator skill

Dip

Dip soldering is done by holding a pre-fluxed board in a frame and lowering it into a static solder pot then removing it to cool. Dip soldering does not usually involve a pre-heat phase, except by suspending the board over the hot solder for some pre-determined time to activate the flux. The dip technique is an older method that was introduced as a way to solder the entire board at once, rather than one component at a time. However, it can be messy and potentially dangerous to the staff because of their proximity to the hot solder pot and from flux fumes in the ambient air.

Pros: Low cost per solder joint; systems range from $1,000 to $5,000 for a non-automated system; relatively fast

Cons: Old technology, low volume; messy and potentially hazardous; not terribly precise, so some bridging may occur between joints requiring inspection and rework

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Editor's Note: This article originally appeared in the November 2015 issue of SMT Magazine.