Control for Cost-Effective Selective Soldering

Christian Ott, Heike Schlessmann, Reiner Zoch
SEHO Systems GmbH, Kreuzwertheim, Germany

Compared to other soldering processes, the selective soldering process is considered as particularly demanding. Structures with small pitches or small distances to neighboring components result in a small process window and provide less room for potential failures.

From conventional wave sold ering we already know that variable parameters, such as the flux quantity, preheat time and temperature or wetting time and solder temperature can play a decisive role for a "high quality" or "low quality" solder joint. These variable parameters are to be considered even more critical in selective soldering processes. Therefore, precision and accuracy of the equipment are a MUST to avoid costly rework. A controlled and reliable selective soldering process is a basic requirement for approach ing a zero-fault-production.

Even potential operator faults should be detected and - if possible - have to be eliminated by the machine. Modern control units and easy to handle software provide the basis for a complete process control and thus build the cornerstone for a cost-effective selective soldering process.

Control functions for the different process steps, as fluxing, preheat and soldering, as well as additional features such as fiducial recognition or process visualization on the one hand are decisive, on the other hand they are helpful tools to ensure a reliable selective soldering process.

This paper will give a comprehensive survey about the single process steps and which possibilities exist to monitor and control them.

The target of a zero-fault production is the main driving factor for the control of the selective soldering process. Only if all process steps are performed absolutely reliable and repeatable, costly rework can be avoided. Control functions which are part of a selective soldering system are independent from the human circadian rhythm.

Particularly for users producing electronic parts for the automotive industry, these control functions will help a lot to proof the stability of their processes and thus ensure a soldering quality at highest level.