Customer: “I need a harness to connect this widget to this gizmo.  The catch is, it needs to handle between 15 and 20 amps and can’t be more than 0.010” thick.  Oh yeah, it must be electrically isolated.  What are my options?”

We get this question occasionally, typically from auto glass manufacturers supplying to the European market, but also from Heavy Equipment glass manufacturers as well.  Typically, in this scenario you have two options, the first being a flex circuit which I have discussed in the past, or two being a “foil” connector which is a relatively unknown product outside of auto glass circles.  The lack of use elsewhere is really unfortunate because it could be used as a low cost design solution in many different places.

What is “foil”?

First, I would like for you to take a look at a couple of our products that use “foil” as a conductor for reference.

Next, we will take a look at the typical construction of this type of connector.

1) We start with a bare copper or tin plated copper foil conductor.  Standard thickness is 0.1mm and standard widths are 6.25mm, 15mm and 17mm.  Other widths and thicknesses are available depending on application, but using these standards allows us to control cost.

2) The foil conductor is then encapsulated with an insulating tape.  As a standard, black or natural (amber) polyimide film is used (Kapton), but other options are available.  The width is usually 3-4mm wider than the foil conductor.

3) Double sided tape can be applied to assist in final assembly.  Tapes that we use include 3M 9473 and TESA 4972, but once again, other options are available.  A die cut pull tab can be added to really make this a valuable addition.

4) The foil is prepared so that it can be mated with a harness of some kind.  This can include an environmentally sealed plastic overmold to round wire or termination, a tab of reflowed and fluxed solder, a termination directly on the foil with housing, a stamped hole, etc. depending on application.

The design discussion can obviously be much more technical, especially with regards to material selection and current capacity.   This post is meant only to be an idea generator, if you have a problem that you think this may solve, call us and lets talk about it in more detail.

If you have an application that has size constraints, I think the advantage is clear when it comes to using “foil”.  It is often assumed that there will be a significant premium to be paid for this option, but that is the beauty in the solution.  Given the popularity of this type of product in European automobiles, there is already an established supply base.  Cost can easily be controlled by using standard materials which are produced on automated equipment.