Simplifying Assembly

New switch base suitable for reflow soldering

With the introduction of lead-free soldering, the problem of high soldering temperatures in temperature-sensitive applications has become more acute. Previously, this has often resulted incomponents such as mains switches only being able to be soldered manually onto the circuit board in a separate manufacturing step after the reflow soldering process. But this does not prevent high temperatures being transferred to the plastic parts of the switch via the contacts and causing deformation with adverse effects on the operation.

In collaboration with a renowned domestic appliance manufacturer, Bär has been looking for away of assembling switches without the heat produced by the manufacturing process affecting the switch. Push button switches of the 3292 range were used as a basis for consideration. The requirement specification made the following demands:

• Suitability for reflow soldering
• Connection using SMT technology
• Easy switch assembly
• Only one more part compared with conventional solutions
• Minimal additional costs compared with standard solution

For this solution, the 3292 switch base was designed as a separate SMT connector suitable for reflow soldering. This switch base is therefore fitted in the continuous reflow soldering process - but can also be fitted manually if necessary. The top part of the switch then only has to be plugged in afterwards. A clip fastener ensures that it issecurely retained.
The temperature-sensitive plastic elements of the switch - housing, actuatorand moving contacts - are not subjected to any high temperatures during this process. This eliminates degradation and damage caused by heat. The switch can be attached either automatically or manually. In both cases, fitting only requires a fraction of the time compared with conventional fixing by means of manual soldering.

The two components of the switch - switch base suitable for reflow soldering and plug-in switch - are assembled separately, ready for fitting, in bar magazines for fully automatic board population.

On most automatic board population machines, these feeders can be incorporated into the existing system without any difficulty. Any modifications that may be required can be carried out by Bär.
The small additional cost of the two-part solution compared with single-part switches is more than compensated for by the enormous time advantages in assembly, and by the additional process and quality reliability that are gained by avoiding the effects of temperature.

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