Dev Log: Wearable Private Cloud

First batch of PCBs

This post will focus on our development on the hardware front. Josef, our CEO, will be sharing about other aspects of the project next week.

The first batch of PCBs have arrived.


On inspection through a microscope, they look like the surface of the moon, whereas they should be almost perfectly flat.  We are trying to solder devices with incredibly small sizes: in the photograph with the gold craters, each of the circles is a pad that we are going to try to solder to.  These circles are 0.285mm across and the gaps between them are only 0.115mm.  The craters are roughly 0.1mm across and about the same deep and they make a connection to some other metal tracks inside the PCB.  


In the picture below, which is from a board that I designed a year ago, it is just possible to see a dot in the middle of some of the gold pads.  This board is the same thickness and has the same number of layers, but the holes have been filled in before the final coating of gold has been added.  This is what should have been done with our boards.


All is not lost though.  We have been able to use one board to prove the mechanical design.  We have wrapped one of the PCBs around the plastic frame that we printed last month and attached an LCD.  From this, we have confirmation that the LCD connector is in the correct place.




The solder paste screens are currently being manufactured.  They are due in this week.  Once we have them, we can use some of the boards to tune the production line.  From this, we shall get one board with the antenna and a test connector.  This will then go to a local facility so that the correct antenna matching components can be found.  As with CB radios, correctly matching or tuning an antenna improves its performance.  We need two different tunings, as some boards will be placed in watch cases and others will be used by the software developers without a case.

When the boards arrived, I measured the coil for the wireless charging.  This is the octagonal spiral you can see on one of the photos.  The QI charging works at 100kHz.  The coil acts as an antenna and also needs to be tuned.  Because there will be a battery inside the box, we have to add shielding to the PCB so that the battery is not heated by the RF.  Hot lithium batteries are generally considered to be best avoided and even though our battery contains only a minuscule amount of Lithium, the shielding is required.  Adding the shielding detunes the coil, so this has to be measured and then compensated for.  The benefit is that properly tuned, it improves the performance of the wireless charging.  The shielding is the silvery pad with the hole in the middle.


The second batch of PCBs are due the first week of February.  We should have everything ready for them.


Martin Layley
Hardware Engineer





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