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I'm trying to use the capacitative touch chip CPT112S for a project. It comes in QFN20 3x3 package size but the pad layout is different to what I expected and so doesn't fit the DIP adapters I have. I'm prototyping and so need to be able to hand-solder the chips. I was expecting a package like this with pads along the edges and not in the corners:

enter image description here

But instead I got one like this which doesn't fit my adaptors as the pads are positioned right in the corners:

enter image description here

I can't find any information about different package types of QFN packages nor whether there are any DIP adaptors out there that I could use. From some of the answers below there is no standard set of package types for QFN 20 packages.

I need to know the following two things:

  1. How can I find out what the specifications are for the package that I have so that I can find the appropriate DIP adapter for it? The product datasheet (found by googling CPT112S-DataSheet.pdf - I don't have sufficient reputation for another link!) doesn't have that information.
  2. How can I identify and therefore specify the particular package type to a PCB manufacturer when it comes time to get some prototype boards printed up?
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    \$\begingroup\$ I am not sure what you are asking for, recommendations for products are offtopic, so a specific place to buy adaptors it can't be. So either buy adaptors, make your own ones or do some dead bug soldering. \$\endgroup\$ – PlasmaHH Sep 25 '17 at 14:33
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    \$\begingroup\$ Doesn't the datasheet have dimensions for the recommended footprint? \$\endgroup\$ – Wesley Lee Sep 25 '17 at 15:04
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    \$\begingroup\$ Unfortunately there is no standard footprint for components like these. Relying on off-the-shelf DIP adapters will severely restrict the parts you'll be able to use. Luckily, modern PCB manufacturing costs have become extremely accessible to hobbyists in the last decade or so. The learning curve is steep but fast. And then you can make anything! \$\endgroup\$ – Dan Laks Sep 25 '17 at 16:04
  • \$\begingroup\$ @DanLaks while they won't work for everything, DIP adapters do have a role - want to evaluate a new chip before you invest in designing around it? Worried something in the surrounding circuitry might be causing a problem and want to try it on its own? The set for common QFN32's I bought a while back has hosted 3 fundamentally different ICs, all of which then ended up on custom boards. \$\endgroup\$ – Chris Stratton Sep 25 '17 at 17:51
  • \$\begingroup\$ @ChrisStratton completely agree. Just trying to nudge the OP a little that custom PCBs are not scary. \$\endgroup\$ – Dan Laks Sep 25 '17 at 19:14
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QFN packages have many footprint variants. Anything from pad pitch (0.4, 0.5, 0.65, 0.8 etc) through thermal pad shape to pad arrangement. You will have to find or design the specific adapter.

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(Not sure if this qualifies as an answer but I can't post screenshots on comments)

From the datasheet you provided: (All on pages 29 ~31.)

Pitch is the dimension "e": 0.50mm

enter image description here

Land pattern:

enter image description here enter image description here

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  • \$\begingroup\$ Thanks very much for the help. A bit of cursory googling has now set me on my way, starting here: learn.sparkfun.com/tutorials/designing-pcbs-smd-footprints I wouldn't have go there without you! \$\endgroup\$ – Xebedee Sep 25 '17 at 21:34
  • \$\begingroup\$ Happy to help. Designing footprints is quite fun and necessary once you start getting into more projects, not always you can rely on libraries on the net. As Dan Lak said, you shouldn't be afraid of trying to make your own PCB. Good luck! \$\endgroup\$ – Wesley Lee Sep 25 '17 at 21:37

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