Electronic – How to make a device in miniSD or microSD form factor


I would like to design and get produced a device in miniSD or microSD card form factor. This is not actually a memory card, it just uses that connector. There are other devices like that, for example Electric Imp. I'm wondering what type of circuit board and what type of outside packaging is used in devices like that?

microSD thickness is only 1mm. There are plenty of chips which are thicker than that, even in the thinnest possible package they come in. Typical circuit boards are 62 mil (1.62mm), the thinnest I have seen is 10 mil (0.25mm). I'm not sure if a multi-layer board can be made in 10 mil in any case. Are microSD memory cards usually made as system in package (SIP) or do they have a board inside? In non-memory devices, what type of board is used (if any) and how do they solve the device height problem?

In a device like this, are the contact fingers on the circuit board or on the case? If on the case, then how does the board connect to them? How is the case made?

EDIT Bounty started. Please describe: How are such devices built? (wire-bond, PoP, encapsulated in epoxy, WLCSP on thin or flex board, etc …) If a board is used, what kind exactly? Who can manufacture these? (board, assembly, encapsulation, …) Any example whitepaper explaining the design or different designs? How to deal with over-thick chips? (for which no thin replacement exists) Thanks!

EDIT The answer below had some good ideas, but I am still looking for a definitive answer. I want a "design guide/white paper" for small form factor encapsulated devices like this, and some pointers to manufacturers. Any good answer will get a bounty.

Best Answer

I am not very sure what are your manufacturing powers, but here are some considerations:

  1. You can use flexible PCBs. Produced on polyimide base they can be 0.20mm thick for two layers board and 0.13mm for one layer board.

  2. You can implement the connection contacts as traces on this PCB. As long as the PCB is flexible you can use one side PCB and to bend it this way in order to provide some space for the parts:

    _________     parts
  3. Some very small parts have to be used, but considering your other questions on electronics.stackexchange.com you already have most of them.

  4. BTW, if it is too expensive, or too hard to put everything in a SD card package, there is another solution, accessible even for an amateurs - put everything in small box that ends with SD card-like connector. This way, the thin part of the design will be only the connector - a piece of PCB with contact tracks:

     connector pcb   / BIG PARTS \
            ===================== |