I've been playing with these through hole reed switches: MDSR-4-12-23. It has been my experience so far that you have to be very careful in handling them, including when bending the leads to 90 degree angles for PCB insertion. It doesn't take much applied force to chip or crack the hermetically sealed capsule.

So my questions are two:

  1. Is there any advice for handling and lead-forming that I should instruct a PCB assembler about as part of my design package?
  2. Is the principle function of the reed switch as a magnetic switch compromised if the capsule seal is compromised?

You need to get a lead forming tool. It will clamp the leads near the body, and then bend the remaining lead without causing any body damage.

A set of thin needle nose pliers to hold the firm should also work.

If you are installing a lot of these, then a form will work best and provide uniform results.

  • \$\begingroup\$ OP is asking about industrial assembly not one off or self assembly. \$\endgroup\$ – Passerby Jan 7 at 23:03
  • \$\begingroup\$ Definitely use a lead forming tool then. \$\endgroup\$ – CrossRoads Jan 7 at 23:07
  • \$\begingroup\$ Any comment on the functional impact of the seal being compromised? \$\endgroup\$ – vicatcu Jan 7 at 23:10
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    \$\begingroup\$ If the seal is compromised then you run the risk (or perhaps insure the certainty) that you'll have units pass factory test and then fail in the field with age. I leave it up to you to decide whether the cost of warranty repairs or the damage to your reputation is worse. \$\endgroup\$ – TimWescott Jan 7 at 23:24
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    \$\begingroup\$ Talk to your assembly house; if they've been around a while chances are they already know how to bend the leads. If Littlefuse doesn't show how to bend the leads in their catalog, see if you can get the attention of an applications engineer to tell you. Frankly, I'd see if I could order them with pre-bent leads -- that way if there were problems it wouldn't be on my head! (And note that there are surface-mount versions that are pre-bent). \$\endgroup\$ – TimWescott Jan 7 at 23:28

The leads of a reed switch are magnet elements, and performance will change if they are bent or trimmed, but presumaby that is not your problem. The leads must be clamped between the bend and the glass capsule during bending, so that stress does not apply to the glass/metal joint.

Jewelers' pliers with a flat jaw and round jaw will produce a consistent bend, and might help.

[roundnose/flatnose pliers]1

If you can use the switches without bending the leads (using clamp or screw-down attachment) that might also be a good solution.


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