microSD card reflow: quick and dirty PCB with Kicad

Ever wanted to add a lot a flash memory to a small microcontroller? NOR flash or EEPROM are ok, but only for small size. For Gbit range, you need NAND, and with NAND comes CCR, LUT, wearleveling, etc… Furthermore, they are darn expensive in small volume.

SD and microSD card are very interesting: they cost nothing, and you just need a SPI interface as the controller is included.

Last night, I thought: “why not reflow a complete microSD card”, and save the cost of the socket, and PCB footprint size. As the card is composed of the same resin as chip casing and pins are flat bellow the microSD card and even gold plated, fore sure it should not be a problem to bring this to 270°C for 2-3 min….

Let’s try!

Here is the pinout

Then let’s create a small board, to try the reflow of a micro SD card and give access with some 2.54mm header.

Lets open Kicad and start with the schematic with Eeschema:

Then PCB new for the board layout:

Let’s submit the gerber files to OSH Park

Total including USPS post mail: 4.10€

That was my fastest board made ever, 1h30 from searching the pinout to the confirmation email!

See you back in few week for the oven reflow test!

Update: the board and the reflow!

First, let’s clean it and apply some flux:

Then some solder on the pads, and flux again:

Time to turn the heating plate and IR reflow on:

Just stir it a bit while it’s hot:

Houston, we have a reflow!

Then time to test: lets scavenge a super cheap reader microSD card reader:

And plug it: IT WORKS! After 3 min under the IR station, it does work.

I think I’ve to increase the pad size, in order to maximize the solder paste.

Now I’m confident sending to production, as I’ve quite a lot of theses cards in trays, ready for pick and place:

 

16 thoughts on “microSD card reflow: quick and dirty PCB with Kicad

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  5. Awesome! You could make the traces a little bigger from the pads as well just in case for better signal flow to the pads to the pins

    Very cool idea and will be much more difficult for people to swipe those micro SD cards!

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  7. Very interesting, I am working on similar design and worked out ok for the prototype. Did you do a production run reflow soldering the microsds? How did it go? Thanks!

  8. So the plastics case is fine for reflow? Was there any sign of deformation?

  9. I didnt got to production with this, as it’s quite risky, and takes a lot of space.
    At the end, I used the molex version where you can stuff component bellow the card:

  10. Tweepy, why did you say everything was fine, and then suddenly say you didn’t use direct reflow in production because it was “risky?” What risk? We could really use your advice because we’re considering using the direct reflow technique in our product.

  11. Everything was fine FOR ONE UNIT, but since it’s not even mentioned in the card’s DS, I cannot take the risk (30K€ BOM) with a 1k production.
    Furthermore, as I said, my board was lacking space, with the molex connector, I was able to fit the MCU bellow the card.
    But you can try it on a small batch (100 units), and come back with your results, I would definitely appreciate.

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