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There are three main soldering methods used in automatic soldering machines: spot welding, drag soldering, and pressure soldering. Soldering machine manufacturers will determine the appropriate soldering method based on the product characteristics of their customers and provide corresponding soldering solutions. Here’s how soldering machine manufacturers specifically decide on the soldering method according to product characteristics:

Spot welding: The weld spots on the product are uneven, and the weld spots must be fully filled. In such cases, a spot-welding method will be chosen—for example, spot welding of PCB boards.

When using a soldering machine to spot weld products, the primary scenarios for choosing this method are either uneven solder joint distribution or high requirements for the fullness of the solder joints. There’s also another situation: although the solder joints on the product are evenly distributed, the components need to be secured in place, so one of the solder points must be fixed prior to soldering. In such cases, spot welding proves highly efficient. Generally speaking, whether it’s soldering electronic chips, assembling components, or performing spot welding, many products exhibit uneven solder joint distributions and have varying requirements for solder plating quality.

Drag soldering: The solder joints on the product are evenly distributed, and the components need to be fixed in place. There are two methods available for drag soldering.

The soldering machine chooses the drag-soldering method primarily because the solder joints are evenly distributed and the spacing between solder joints exceeds 0.1 millimeter. Products of this type require fixed inserts. If the direct distance between two solder joints is less than 0.1 millimeter, fixed inserts are not necessary. Using drag soldering in such cases could lead to issues with the solder's connection to the product. For these types of products, wave soldering or reflow soldering is the fastest option. The advantage of drag soldering lies in its ability to save time and improve the welding efficiency of automatic soldering machines.

Welding: The product solder has tensile requirements, and the solder joints are relatively uniform.

In solder joint testing, pressure welding primarily requires tensile strength and uniform distribution of solder joints. For products without through-hole components, pressure welding can be used. If wave soldering or reflow soldering is employed, especially for products with tensile strength requirements, it’s best to use a soldering machine for soldering. This approach provides greater assurance to customers whose products have specific tensile strength requirements for soldering.

Reasons for poor soldering quality in soldering machines:

1. Cold welding

During soldering with a soldering iron, if the flux temperature is too low or the heating time is insufficient, the solder may not fully melt and penetrate, or the solder surface may appear dull and cracked.

2. Excessive solder

Tin deposits that form solder joints; if the amount of solder in the soldering machine is too small to adequately coat the solder joint.

3. The solder on the solder joint surface forms sharp spines.

This is mostly caused by insufficient heating temperature of the soldering machine or inadequate flux, as well as improper angle when the soldering iron is removed from the solder joint.

4. There is a layer of rosin between the solder and the component or the printed circuit board, resulting in poor electrical contact.

If the rosin is insufficiently melted during soldering, a yellow-brown rosin film will remain beneath the solder joint. If the temperature is too high, the rosin will turn black. In both cases, the former can be repaired using a soldering iron. For carbonized residues, it’s necessary to re-tin the components, clean the soldering area or printed circuit board surface, and then resolder them.

5. Excessive flux around the solder joint, with excessive rosin residue.

When a small amount of rosin remains, gently heat it with an electric iron to allow the rosin to evaporate, or use a cotton ball dipped in anhydrous alcohol to wipe away any excess rosin or flux.

6. Excessive solder

Excessive solder on a soldering machine can cause short circuits between component solder joints. This is especially important to note when using a soldering machine for automatic soldering of ultra-small components and miniature printed circuit boards.