PCB Assembly Services - Screaming Circuits: Pitch Switching


Pitch Switching

I recently started reading the magazine Chip Scale Review. It's a different take on things than I'm used to. Most of what I read for work is in the engineering and assembly realm, but this one goes back to the component packaging. I think it will be a good one in terms of keeping up on what sorts of things we'll need to be assembling in the future.

So far, I haven't seen anything really scary in it. There is talk of .3mm pitch BGAs, but those aren't totally new. I'm not sure if we've done any .3mm pitch before, but we've been doing .5mm for years and have done plenty of .4mm pitch as well, even in package-on-package (POP) forms.

Pitch switching adapter Speaking of really fine pitch BGAs and CSP type things, one topic I found interesting has to do with pitch switching adapters. It's basically a small PCB platform that has an underside footprint of a 1mm or 1.27mm pitch BGA and a land pattern on top for a fine pitch BGA. It has solder balls on the bottom, so once sandwiched together, it's treated just like a big BGA for assembly purposes. [Credit where credit is due: The image I'm using came from the Aries Electric web site.]

Such a part can negate the need to re-spin the PCB if your big part is updated and replaced in a new fine-pitch form-factor. (Although, personally, I can only imagine that if the chip is rev'ed, there will be some other change that has to be made to go along with it). The theory is, that if you've got a really expensive design, this might be a viable option allowing you to upgrade without a relayout.

Certainly though, at the very least, this could allow you use some newer fancy chips without having to resort to filled micro vias and tiny trace & space advanced (expensive) pcbs. Could be quite handy and same some money.

Duane Benson
Platform shoes are back!


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The concept of using a 'pitch switcher' to change from one pitch to another is also used for test sockets in semiconductor test. Here we call it a Pitch Transformer. It is a socket with a large array on the base, say 0.8mm pitch, and the device pitch in the socket, can be down to 0.1mm pitch. This lowers the cost of the test board and gives the designer more room for routing. It also enables testing of WLCSP devices. Paricon Technologies (www.paricon-tech.com) uses their membrane contact system to achieve this and achieves bandwidths of 40GHz -1dB; Equiptest Technologies (www.equiptest.com.sg) achieves it using spring probes. The Pitch Transformer sockets are self contained and plug-and-test. Considerable costs savings can be made in test and when used for demo boards. If you need separable contacts these are the way to go. They are all available today. Contact - sales@coretest.co.uk - for more information.

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