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SIM card miniSIM to microSIM conversion, 3D-printed adapter

Problem

The cellphones, at least the sane not-US-only ones, are not bound to the phone number. The authorization data and procedures are housed in a subscriber identity module, also known as a SIM card.

The older phones used a mini-SIM size, or 2FF. This was introduced in 1996.

In 2003, this card, huge with its 25x15 mm footprint, was joined with a micro-SIM format, or 3FF, with identical chip and contact pad layout but some unneeded plastic trimmed off, to a 15x12 mm size. Since about 2010 it started appearing in smartphones.

(In 2012 yet another format appeared, of course - a nano-SIM, or 4FF. This was first used in an iPhone 5 and since was adopted for some other phone models.)

Getting an older-sized SIM exchanged for the newer kind involves physical visit of the operator and is rather annoying. A DIY approach is therefore desirable (there are many tutorials online).

In some cases there's a desire for backward compatibility - e.g. when the migration to the new phone involves some hassle and a rollback capability is needed. Here, a bracket/adapter for the micro-SIM to the mini-SIM is needed. To obtain it, a logistical operation is usually needed - going to a shop, visiting the operator, or ordering online. A simpler operation is again a DIY approach. A 3D printer can be easily leveraged here. (A laser cutter can do the same job.)

Solution

A dimensioned drawing was obtained easily by an image search, from a librecad forum. The drawing was converted to an OpenSCAD draft.


drawing

Drawing

The drawing was done using extruded polygons, with added size adjustment constant that gets added to (or subtracted from) the dimensions, to adjust for a kerf width (for laser) or for the width inaccuracy of the extruded filament (for 3D printing). The addition does not perfectly conserve the length of the cut-off edge, which should not matter for the small intended values of the kerf adjustment.

The file contains a model of both miniSIM and microSIM. They can be used as standalone if needed.


OpenSCAD drawing

Printing

The adapter was printed with 0.2mm layer thickness (0.3mm first layer) using PLA, in total of three layers.

Two adapters were printed, with kerf adjustment -0.1mm and -0.3mm. The latter was found to be too small and fitting the socket too loosely.


Adapter and SIM

Adapter and SIM

Adapter and SIM

Adapter and SIM

Cutting the SIM

The printed adapter was used as a pattern to draw the micro-SIM outline on the mini-SIM. Scissors were then used to cut the card to proper dimensions, using the bracket to check the size and trimming the edges until the card fitted the hole.


Adapter and cut SIM

cut microSIM in adapter

The fit was then validated in the new phone, together with test if the card did not lose functionality.

The card was then placed back to the old phone, using the printed adapter, and tested as correctly functioning.


adapter and microSIM in phone

Printing from different materials

In addition to PLA, other materials were tested.


All

Blue ABS

The printing was successful. A relatively hot extruder temperature was used (225 °C), with 80 °C bed. The printing was almost flawless, with slight deformations where the hot nozzle remelted the polymer. This defect is easy to remove with a file, if it shows to mechanically interfere with the card slot.


Adapter from ABS, top

Adapter from ABS, top

Adapter from ABS, bottom

Adapter from ABS, bottom

White polycarbonate

The printing was grossly unsuccessful. At 245 °C it extrudes and fuses fairly well, and sticks well to a 95 °C bed. It however grossly warps, even with mere three layers. The material apparently needs a heated chamber.


Adapter from polycarbonate, top

Adapter from polycarbonate, top

Adapter from polycarbonate, bottom

Adapter from polycarbonate, bottom

Clear PETG

The printing was fairly successful. At 220 °C it extrudes and fuses well. At 80 °C bed it sticks well, but stays soft and deforms readily during removal attempt. (See leftmost two attempts.) At 60 °C it sticks also, but warps noticeably even at mere three layers, although way less catastrophically than polycarbonate. A somewhat time consuming but working solution is printing to 80 ° bed and then letting it to cool to 60 °C before removal.


Adapter from PETG, top

Adapter from PETG, top

Adapter from PETG, bottom

Adapter from PETG, bottom

Conclusion

The PLA prints well but is unsuitable for high temperature environment of the phone due to its low softening temperature.

The ABS prints well and behaves well.

The polycarbonate cannot be printed without heated chamber due to very extensive warping.

The PETG can be printed well but its behavior on the heated bed puts a question to its performance at elevated temperatures.

The ABS is therefore a clear winner of all the materials tested.

TODO


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