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I am thinking of using some Hirose DF40 PCB stacking connectors to stack together a bunch of PCBs. Each pair of PCBs would be connected by two connectors for mechanical stability.

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These connectors do not have locating pins, so they rely entirely on the self-alignment effect during reflow to pull them into the correct position. Now, I can imagine that these connectors, being 0.4mm pitch, will self align pretty accurately in the X axis, but surely not so well in the Y axis.

This might not be a problem if only one connector was being used, but two connectors have to be lined up fairly accurately between the two PCBs. How well will they self align in the Y axis?

Does anyone have any experience with similar connectors in a similar situation?

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Are you sure there isn't a variant that comes with locating pins? – Olin Lathrop Mar 31 '12 at 15:57
Not that I could find. The DF12 does have pins, but it's larger. – Rocketmagnet Mar 31 '12 at 15:57

2 Answers

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I would either ask the manufacturer for an app note on the subject, or I would choose a different connector with alignment pins.

Not to belittle anyone on this web site, but unless someone here can give you the exact PCB footprint that they used on that exact connector, the exact make/model of solder paste, the exact dimensions for the solder stencil (width, length, and thickness), and the exact temperature profile for the reflow oven then I wouldn't trust their information.

The problem is that the dimensions of the PCB pad, and how the melted solder flows on that pad, will effect the self-aligning process. More or less solder will effect things. Different solder alloys will effect it. Etc. Just knowing that this guy was successful isn't enough to guarantee that you'll be successful. You need to know everything to a precise degree, and I honestly doubt that anyone here will be able to give you that level of detail.

So... Talk with the manufacturer. If they want to sell you stuff then they should be able to help. And if they can't, then use something else.

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You're right, one person's testimony would be useless. But if it turns out that these connectors always seem to work, or don't mind misalignment, then that would be a good argument in their favour. – Rocketmagnet Mar 31 '12 at 16:31
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@Rocketmagnet I don't believe that there are no other choices. I have connector manufacturers knocking on my office door all the time, so much that I have to shoo them away. Most of them have connectors similar to what you mention. And most of them will also do semi-custom versions. If you can't find an alternative then you're just not asking the right questions or you're talking to the wrong people. – David Kessner Mar 31 '12 at 16:35
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@Rocketmagnet Don't talk to the Distys. Talk to the manufacture or their local rep. Samtec, Hirose, Amp, Molex, Tyco, etc. Tell your local rep what your needs are and let them suggest a connector that will work. And I do mean TALK. Most of these companies have too many connectors to wade through online or in a catalog. Go to the Samtec web site (samtec.com/highspeed/mezzanine_strips.aspx) and request free samples! Use your local reps, that's what they are there for. Make them do the work! :) – David Kessner Mar 31 '12 at 16:48
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Hey, nice differential pair connectors! Sadly too tall. Thank, I'll try talking to the reps. Still, I'd love to know if anyone has had any luck with self-aligning connectors. – Rocketmagnet Mar 31 '12 at 16:54
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I have used those connectors on PCBs with the Hirose specified pad size (one 40-pin and one 20-pin in the same configuration as you are suggesting). I both hand soldered and reflowed them with no special attention and excellent results. Yes, only one person's experience but I would recommend getting a few samples and doing some soldering tests if you are still apprehensive. For size and pin count, there are few other parts that have the same density as the DF40s. – spearson Mar 31 '12 at 20:10
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up vote 1 down vote accepted

I can now answer this question myself.

The answer is that they probably self align accurately enough. The connectors actually allow for about 0.3mm misalignment in the Y direction. I actually glued two pairs of connectors to two scrap pieces of PCB, so they probably weren't well aligned. I was able to plug the PCBs together both ways round, despite probable angular misalignment between the connectors.

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