A short circuit between the SIM_1V8 pin and GND in nRF9160

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Asbjørn — Mon, 26 May 2025 11:49:23 GMT

Hi,

I'll leave this thread open and try to reply the best I can. Unfortunately soldering issues in prototype runs can be quite challenging as they may involved more manual steps that could change the behaviour of solder and equipement. The footprint of the nRF9160 is complex compared to regular QFN packages or WLCSP.

My intention was not to bury it, just challenging to make sure the replies go to the right person.

With shorts like you've seen here some of the items to check would be:

Amount of solder applied, is it evenly applied? By machine or by hand?
Visual inspection:
1. Is the SIP mounted level? Can you confirm that the SIP is flat on the PCB?
2. Compare the before solder situation across boards (ref point 1)
Size of GND plane on the PCB and number of internal layers. If the GND plane is large it might radiate more heat and not warm up evenly on all PCBs. Some boards might be fine and then some located towards edge or of center from the heating source might not get the same temperature profile. It could be close, but distort the outcome. Again, this process is not unusual to be influence by human operators, but don't know the situation for each specific customer, but it's worth seeing if temperature is the same on all boards after the same time and also if a round of reheating/rework will clear up the issuess.
Solder stencil used, thickness of it. Is the manufacturer familiar with such stencils, is it possible to change resolution or thickness to try to have more control of the solder applied. Does the stencil match up as it should or exptected?
X-ray as to debug if possible, can you see shorts on the xray, are they in the same location on all boards or randomly located?

I'm sure there are more steps as well, but the amount of solder, distribution of it and heating often comes up with variations in prototype builds.

Best regards

Asbjørn

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

RemcovH — Fri, 23 May 2025 13:17:58 GMT

Please do not have this thread moved to private.

Yes we are 'hijacking' this specific case becuase others are experiencing the same issue with the same behaviour. We all want to know what a possible solution can be (that maybe can differ between design, but it is a start). By having this thread changed to private, it will be a sign of "bury your head in the sand".

We are still investigating with or production partner if there is something that can be improved on their end (currently a new batch going into production).

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Asbjørn — Tue, 20 May 2025 08:36:23 GMT

Hello Bartlomiej ,

I'm not sure if this case is still open from your end. It seems to be added on by others now that are not necessarrily related to your case. If you still have further questions, may I suggest we put this case as "Private" to prevent others from cluttering your HW specific issues? We can return it to "public" after we've resolved your issue if that it what you'd like to.

Best regards

Asbjørn

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Asbjørn — Tue, 20 May 2025 08:25:16 GMT

Hello gkrusi,

Didn't catch your comment and question until now. I don't know if you are working on the same HW or have a diifferent setup? I'd encourage you to create your own ticket here to track your issue.

Best regards

Asbjørn

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

gkrusi — Tue, 29 Apr 2025 10:21:38 GMT

Hello Everyone,

We are experiencing the same issue with the silicon SICA B1 2230JF. Some boards from two different batches are exhibiting the described problem. The IC shows a short between the SIM_1V8 pin and GND, even after it has been unsoldered.

We have not identified any design flaws, and everything appears normal on the X-ray inspection. Other batches of ICs do not seem to have this issue.

Do you have any recommendations on how we can eliminate this problem?

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Asbjørn — Thu, 06 Mar 2025 15:02:02 GMT

Hello RemcovH,

I initially though you were following up from the same company and batch that Bartlomiej is, but I see now that you are working on different product, but see similar behaviour from small production run.

Firstly, since this is a different board and setup, I think it would be better to create a separate DevZone ticket to track your question on and then we reference this case. It does seem like you are seeing similar outcome. When it comes to your question about quality, we do from time to time see customers that are doing small batches come back with similar questions, but not from larger scale builds.

We suspect it's related to the solder paste used, the solder stencils and generally the assembly heat transfer through the board that creates this. On smaller batches it's often more prone to human judgements on times and temperatures, so you'll see some differences. We don't think there's just one issues with these, but the package is challenging on small scale productions runs.

So if I may, please create a separate ticket on this for your scenario and we'll work through the behaviour. Link to this case so others can see if you'd like to.

Best regards

Asbjørn

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

RemcovH — Tue, 04 Mar 2025 12:56:33 GMT

Hi Asbjørn,

Sorry for replying on an older chat. Only I have the same issue.

We had 2 production runs:

1. First prototype run of 4 fully assembled PCB's by a good production company. From these 4 PCB's had 2 issues with the SIM_1V8.

2. Second run of 16 assembled PCB's by the same production company (they also installed these PCB's in the final enclosure). From these 16, one had an problem with hte SIM_1V8.

Both issues, 3 PCB's in total, had the exact same behavior as is described by Bartlomiej.

When NRF9160 is soldered on the PCB, there is a short (less then 3 ohm) on the PCB on the SIM_1V8 trace.
When I remove the NRF9160, there is no short on the PCB SIM_1V8 trace.
If I measre the NRF9160 between the SIM_1V8 pad and any GND_Shield pad.

Yes there were changes on the PCB, only those were not related to the NRF9160 or the eSIM to which the SIM_1V8 is connected. The production company we use, also regulary verify if there reflow process is correct.

If they manage to produce 17 out of 20 correct PCB's I deduce there is not something inherently wrong with the production process. There most be something else that makes the SIM_1V8 very sensitive. I assume you would have had more quality issues from other customers. is this correct?

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Asbjørn — Fri, 08 Nov 2024 13:44:56 GMT

Hi Bartlomiej,

I assume the resistance along the line from SIM_1V8 to VCC on U2 and VCC on J1 are all ok with the SiP removed? Ok as in you see infinite resistance/open circuit once the SiP is desoldered from the failing prototype? What sort of resistance do you measure along SIM_1V8 and VCC on U2/J1 on the failing prototype that still has the SiP soldered on?

The most likely cause is unfortunately something has shorted two or more pads on the SiP during the manufacturing process. How long were they running before you started probing the SIM_1V8 lines?

Best regards

Asbjørn

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Bartlomiej — Thu, 07 Nov 2024 14:52:00 GMT

This is the schematic corresponding to the SIM. The SIM bus is connected directly to the SiP. The U2 is the EMI filter for the SIM interface.

This is the first working prototype. The yellow line is the SiP power supply (3.3V), the blue line is the 1V8_SIM. The 1.8V is always present.

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Asbjørn — Thu, 07 Nov 2024 12:38:41 GMT

Do you have any components between the SIM_1V8 pin on the SiP and the SIM card holder itself? Did you do any changes to the component selection between the two prototype runs?

I assume on the first prototype run the SIM_1V8 line goes up all the way to 1.8V and the duration, 244ms, is the same?

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Bartlomiej — Wed, 06 Nov 2024 13:59:16 GMT

Hello Asbjørn,

[quote userid="2729" url="~/f/nordic-q-a/116062/a-short-circuit-between-the-sim_1v8-pin-and-gnd-in-nrf9160/509235"]You say that you could initially see a few mV on the SIM_1V8 pin when powering up the prototypes, but it only lasts for a short duration. It would indicate that the SIM_1V8 pin on the package is trying to start it up but there's a short and the regulator collapses.Did you capture this behavior on any tool?[/quote]

Yes, I have recorded it. The picture below shows the behaviour. The picture shows two different bords. The yellow line is the SiP power supply (3.3V), the blue line is the 1V8_SIM. About 1s after powering up, the 1.8V line spikes. In one case the voltage reaches 200 mV and in the second 6 mV, in both cases the spick duration is 244 ms.

[quote userid="2729" url="~/f/nordic-q-a/116062/a-short-circuit-between-the-sim_1v8-pin-and-gnd-in-nrf9160/509235"]Have you removed the nRF9160 SiP from both of the two failing prototype boards?[/quote]

Only one was removed. But the second board has the same behaviour and the resistance between SIM_1V8 and GND is also zero.

[quote userid="2729" url="~/f/nordic-q-a/116062/a-short-circuit-between-the-sim_1v8-pin-and-gnd-in-nrf9160/509235"]Wihtout knowing more about the layout and changes, could there have been some changes to the soldering process and stencils used to mount the SiP on the latest prototypes that could have added more solder than intended or distributed it differently?[/quote]

I don't know anything about it, the settings and parameters for production and assembly were the same as before. I think it will be difficult to get this information from the factory.

[quote userid="2729" url="~/f/nordic-q-a/116062/a-short-circuit-between-the-sim_1v8-pin-and-gnd-in-nrf9160/509235"]Have you tried soldering a new SIP onto one of the kits from the second build run? What resistance are you measuring between SIM_1V8 and GND on a SiPs that haven't been mounted on any boards yet?[/quote]

Now I don't have it, I have to order the new SIP. When the order arrives, I will check it.

It is worth saying that the other peripherals I use on the prototype in the processor work fine.

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Asbjørn — Wed, 06 Nov 2024 12:50:57 GMT

Hello Bartlomiej,

If there's a short between the SIM_1V8 and GND on the package it indicates that the internal paths have broken down and the chips are broken unfortunately.

You say that you could initially see a few mV on the SIM_1V8 pin when powering up the prototypes, but it only lasts for a short duration. It would indicate that the SIM_1V8 pin on the package is trying to start it up but there's a short and the regulator collapses.Did you capture this behavior on any tool? Have you removed the nRF9160 SiP from both of the two failing prototype boards?

Wihtout knowing more about the layout and changes, could there have been some changes to the soldering process and stencils used to mount the SiP on the latest prototypes that could have added more solder than intended or distributed it differently?

Have you tried soldering a new SIP onto one of the kits from the second build run? What resistance are you measuring between SIM_1V8 and GND on a SiPs that haven't been mounted on any boards yet?

Best regards

Asbjørn

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Bartlomiej — Wed, 06 Nov 2024 08:25:33 GMT

Hello Asbjørn,

Thanks for replay.

To clarify my problem, I removed the nRF9160 chip and did the measurements (resistance measurements). The PCB without chip, has no short circuit issues, it means the resistance between SIM_1V8 and GND is infinite (no short circuit), also in other lines on SIM lines.

[quote userid="2729" url="~/f/nordic-q-a/116062/a-short-circuit-between-the-sim_1v8-pin-and-gnd-in-nrf9160/509154"]What did change between the two prototype runs with regard to layout? Anything related to the GND around SIM_1V8 or some of the SIM_1V8 pin itself?[/quote]

The only change in the SIM lines between the current and the last prototype is a slight offset of the lines. In my opinion, this does not affect the problem discussed.

[quote userid="2729" url="~/f/nordic-q-a/116062/a-short-circuit-between-the-sim_1v8-pin-and-gnd-in-nrf9160/509154"]You say the short circuit is within the nRF9160 chip itself, are you able to explain this a bit more? Are you saying there's solder on the chip/SiP itself short circuiting these two pins? Are you able to share pictures of this?[/quote]

I performed the resistance measurements only on the nRF9160 chip, which is removed from the PCB. The resistance between SIM_1V8 and GND is 0 ohm (short circuit). The chip/SiP does not show any solder shorting of the pins, it is only when measuring the resistance that you can see that there is a short circuit.

So if there's no setting for the 1V8 SIM, it looks like the actual chips are broken, but it's interesting why two chips have the same problem?

RE: A short circuit between the SIM_1V8 pin and GND in nRF9160

Asbjørn — Tue, 05 Nov 2024 15:35:05 GMT

Hello Bartlomiej,

There isn't a setting for the 1V8 SIM supply that should have changed. Given that you are able to recover the short circuited ones by fixing the soldering between SIM_1V8 and GND I would suspect that something has changed on your layout of the board or something in the assembly procedure for the prototype run.

What did change between the two prototype runs with regard to layout? Anything related to the GND around SIM_1V8 or some of the SIM_1V8 pin itself?
Did the assembly house change some of the solder mask or solder flow between the two build runs?
You say the short circuit is within the nRF9160 chip itself, are you able to explain this a bit more? Are you saying there's solder on the chip/SiP itself short circuiting these two pins? Are you able to share pictures of this?

Best regards

Asbjørn