Why are the inner pins (sockets) staggered like this? Moreover, why are the inner sockets even necessary? I don't imagine they expect any voltage between inner and outer sockets?

 

The outer holes are called castellated holes for surface mounting. The inner holes are staggered for a "snug fit" of the through-hole pin header (to make hand soldering without a fixture a little easier).

 

Here is an example of a castellated board soldered to another board. In this case, nothing but a carrier. More often, it would be to a larger board that is incorporating the functionality of a module or dev board, sometimes only during prototyping.

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Here is an example of a castellated board soldered to another board. In this case, nothing but a carrier. More often, it would be to a larger board that is incorporating the functionality of a module or dev board, sometimes only during prototyping.

View attachment 259638​

If so, why are inner and outer pin on the same rail?

 

If so, why are inner and outer pin on the same rail?

I don't understand your question. The smaller board in this case doesn't have holes for .1" headers and SparkFun wanted to turn it into a breakout board by adding them. The castellated edges allow it to be soldered to a board that can accommodate the headers.

I have occasionally resorted to soldering headers into castellations but it's difficult and not as mechanically sound,

Does this answer your question? If not, could you explain?

 

If the question is why two sets of holes -- it is to give you two mounting options (SMT or through-hole).

 

If the question is why two sets of holes -- it is to give you two mounting options (SMT or through-hole).

If that is the question, I never would have guessed it given all the information already provided in this thread.

 

The staggered holes were developed by a guy at Sparkfun. They are called lock patterns, and are designed to hold a header perpendicular to the pcb while soldering. See the story and details here.

 

If that is the question, I never would have guessed it given all the information already provided in this thread.

I can see that better description could help, but at least for me, i saw it immediately, even before zooming into the picture or reading the post. Maybe because i am stickler to ordering things certain way, just coincidence or maybe the (still) good eyesight. Word staggered confirmed it.

Thanks Jon for reference.

Extra holes can be useful of one decided to use stacking header for example for breadboard. For final product, pin array can be omitted and module can be soldered directly to target PCB as Yaakov has shown. Basically it is for flexibility...

 

I can see that better description could help, but at least for me, i saw it immediately, even before zooming into the picture or reading the post. Maybe because i am stickler to ordering things certain way, just coincidence or maybe the (still) good eyesight. Word staggered confirmed it.

Thanks Jon for reference.

Extra holes can be useful of one decided to use stacking header for example for breadboard. For final product, pin array can be omitted and module can be soldered directly to target PCB as Yaakov has shown. Basically it is for flexibility...

Sorry, I don’t understand your point. I knew there were two sets of pads, one being castellations. I knew the TS asked two questions, “why the staggered holes?” and ”why the second set of half holes?” The questions were answered, well, by @Scott Moore in post #2. I added a photo to try to help the TS picture how that would work.

He replied to me in post #4. But, in retrospect, he probably should have replied @Scott Moore because his confusion seemed to be with his answer. So, his reply to me didn’t make sense. I was trying to fit it into context, which would have been, as near as I could work out, a question about the castellations, and the holes on the carrier board that appeared on the photo I posted. I didn’t have any reason to imagine he was returning to his original question which seemed answered pretty well.

So, I had no problem at all with understanding the original questions of the TS, rather the one he asked me.

 

agree.. i misunderstood your post.

 

I don't understand your question. The smaller board in this case doesn't have holes for .1" headers and SparkFun wanted to turn it into a breakout board by adding them. The castellated edges allow it to be soldered to a board that can accommodate the headers.

I have occasionally resorted to soldering headers into castellations but it's difficult and not as mechanically sound,

Does this answer your question? If not, could you explain?

Ah, now I get it. I somehow imagined that you were meant to surface mount it and mount pins _at the same time_.

A little annoying, that staggering. I want to put it on a breadboard and it's a little annoying to have different numbers of available holes per pin. I can't imagine a reason I'd need more than one hole per pin but still. Never mind the fact that I have to break the pin assembly into much smaller pieces than I'm used to.