In today's cost-conscious environment, the ability to efficiently manufacture a product has driven the electronics industry towards more automated processes and streamlined production facilities. Despite this reality, the need for hand-soldering operations remains an integral part of most manufacturing processes. Whether it is the need to attach a large connector, conduct a field modification, or to rework a non-compliant item, hand-soldering operations require personnel with the proper skills to complete the job. The use of the proper, well maintained, equipment is paramount to completing the task in a timely manner while maintaining a high level of quality.

The proper maintenance of soldering equipment is often the most overlooked problem in hand-soldering operations. Fortunately, a few easy and repeatable practices regarding soldering iron tip care can eliminate a wide variety of issues before they become a problem. Proper tip care will extend the life of the tip and cut down on the need to frequently replace oxidized or pitted tips that are no longer usable.

The goal of any high quality soldered joint is the formation of a good intermetallic bond (Figure 4-1) between the solder alloy and the connection contact area (e.g., the wire or component lead, and the land, pad, or terminal).

The following practices will help ensure acceptable soldered connections and prolong the life of the equipment used in common hand soldering operations.

• First, select a tip that is the proper size and geometry for the connection to be soldered (match the width of the tip to the diameter of the pad). While this may seem like common sense, it is frequently the most overlooked practice. It is not uncommon that a technician will choose too small a tip size and try to compensate for poor heat transfer by increasing the temperature of the iron. The problem then becomes two-fold since you have an insufficient area for adequate heat transfer and increased oxidation by increasing the tip temperature. Use the correct tip size and temperature to yield better results.
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• Select the lowest tip temperature needed to facilitate solder reflow. The correct temperature depends on the type of solder alloy being used. Lead-free alloys have higher melting points than tin/lead alloys and often have a frosted or grainy appearance (in the final connection). A grainy appearance on a tin/lead connection is a clear indication that the tip temperature is too high. If a connection is being made on a multilayer board with an internal ground plane, the ground plane acts as a heat sink. Auxiliary heating is needed to overcome the heat sink effects.
• "Idle the tip!" This term refers to the practice of coating the tip with a thin film of solder before returning it to its holder. This thin film of solder will be oxidized instead of the surface of the tip, dramatically extending the life of the tip.
  • First, wipe the tip on a clean, slightly damp sponge to remove oxidation and excess solder. A coiled brass wire pad can also be used to remove excess solder.
  • Only use sulfur-free sponges that are intended for electronics applications.
  • Use deionized water to slightly wet the sponge, never use tap water (the addition of fluorides to drinking water may be beneficial to public health, but causes a multitude of problems in electronics assemblies).
  • Replace sponges at regular intervals and when they become dirty. Replacement sponges are inexpensive and this simple practice will help avoid introducing contaminates.
• When soldering, do not apply downward pressure on the joint being soldered. Simply rest the tip of the iron on the joint to help establish a heat bridge (a small bead of solder on the tip will also aid in forming a heat bridge). Downward pressure will not aid in solder reflow. It will, however, cause undesired mechanical stress on the connection area and may result in lifting the pad.
• The solder should be fed to the connection, not to the tip. Once a heat bridge is established, the connection will melt the solder and the solder wire should be moved around the connection to ensure adequate coverage.
• Finally, always turn equipment off when not in use and never use tips for purposes other than what they are intended. Any breaks or cracks in the plating of the tip that results from improper usage will drastically reduce the lifespan of the tip, or at the very least, interfere with its heat transfer capabilities.

Contact the EMPF at 610.362.1320, via email at helpline@empf.org or visit the website at www.empf.org for more information or advice regarding proper equipment care and preventative maintenance.