A replacement for the HP-41 zebra connector

[mfleming]

(04-19-2017 02:06 AM)Dave Frederickson Wrote:  Hi Mark,

The dimensions look really good. I measured the distance between contact areas, the plus signs in the pic, and measured 0.46". Your pic looks like 0.50".

Do the shaded areas at the top and bottom represent anything? Was your plan to not have a coverlay to reduce cost? Do you think there's any advantage to a narrower trace/space, like 5/5?

Dave

Hi Dave,
That's good information about contact spacing to have. I did assume 0.05" between contacts from a quick glance at the image you posted. Much better to have an actual measurement of the distance. Could you also measure the width of the contacts and the gap between them? I was estimating the gap to be around 0.02" and that gap distance is important in terms of trace width.

The flex contact width obviously must be less than the gap between PCB contacts to avoid shorting two PCB contacts together. I was making the flex width about half of the estimated gap in case there was any skew in the flex with respect to the PCB. I assume the axis of the flex will be a little off angle with respect to the PCB axis since you're assembling and mounting the connector by hand. As to making the traces narrower, I'm close to what the PCB house can handle, but could probably get the traces a little smaller.

The hatched areas at top and bottom are the exposed and plated flex contacts that make contact with each PCB. The exposed contacts can be gold plated on request (adds to the price, of course). Normally every PCB is coated with a protective layer, usually green, but can also be blue or red. Contacts and solder points that need to be left exposed are indicated by a "keepout" layer, which is the hatching you see. A flex circuit bonds a protective plastic layer over the base layer and the copper traces instead of the coating used on a PCB.

I went ahead and put a keepout around the entire contact area for two reasons. One was because the remaining cover area between traces was so small I was certain a reviewer would ask to have them removed. The other reason is that the cover material between traces would act like a standoff, keeping the flex contact just above the PCB contact it is supposed to touch. Not a big deal in the 41 flex design, given the flex contact is 0.1" wide and the cover material is about one-hundredth that thickness. The exposed flex contact will easily bow downward under pressure to touch the PCB contact. Not so with yours, the ratio being ten or less. Best to have no interference if possible.

I did do a quick online estimate as opposed to a formal quote for the 71B flex. As expected, there is a minimum charge. The piece count per cost increment is proportional to the flex area though, so you wouldn't bump up to the next cost level until more than 100 units are ordered (wish my design were that way!)

This brings up the same question I'm posed with; Are there enough people interested in a repair option like this that you can recover some or all of your minimum investment by selling your excess pieces to them? (I assume you don't need to fix 100+ 71B's!) I'm thinking the next step would be to do a poll and see how many people might actually want one of these - 71B flex or 41C flex.

Thoughts?
~Mark