Soldered Castellated XL51822 short - Page 1
Forum section: electronics / general

author: michelvachon
author_rank: Newbie
timestamp: November 16, 2022, 01:22:08 am
content: My nordic chip's power consumption increases dramatically after soldering it to my custom PCB.It goes from 4uA to 10000uA.Before soldering, the resistance between ground and VCC is around 2.5 megaohms but after soldering, it sometimes decreases to 50kOhms.It looks like my soldering is shorting ground to VCC.Is this the cause of the increased power consumption?XL51866 castellated chip:Custom PCB:Even after unsoldering, removing all solder and flux,the XL51822 chip's power consumption remains high,so I suppose I damaged it.I tried on about 4 identical chips, all the same.To measure power usage without the PCB, I use my homemade pogo pins fixture, please don't laughI've had prior success soldering ESP32 castellated modules on my own PCBs.So I really don't understand what I'm doing wrong here.Any suggestions ?ThanksMike

author: thm_w
author_rank: Super Contributor
timestamp: November 16, 2022, 01:32:21 am
content: It looks like you just hand soldered Vcc and Gnd and that was it, hardly seems possible to damage the board just based on that.- Sure its nothing to do with what program is loaded to the device? Did you load any code.- What voltage are you supplying the module with? Its rated for 3.6V maxOne small issue: you have uncapped vias under the module, which is not great, if they were in the wrong spot it potentially could short out to the module.

author: michelvachon
author_rank: Newbie
timestamp: November 16, 2022, 01:42:06 am
content: Yes I have loaded my code on it of course.I tested it with 2 programs in fact.One is just putting the chip to sleep, which consumes 4uAh.The other one has bluetooth enabled.The power usage on this one varies between 4uAh and 60uAh,which is expected based on the advertising interval of 750ms I set.I'm supplying 3.3v.You are right about uncapped vias, a rookie mistake.But I tested everything with a piece of paper between the XL51822 and the PCB, covering all pads except for VCC and ground.

author: thm_w
author_rank: Super Contributor
timestamp: November 16, 2022, 10:34:14 pm
content: OK so you did program the same code on a good new unit, in your pogo jig, and it consumes 4uA, not the bad 10mA level.Maybe the pads on your PCB, even though they were not soldered, had connected and caused some short.I do see those two vias under the device look unusually close together.Seems unlikely though.Maybe post the schematic?

author: 48X24X48X
author_rank: Frequent Contributor
timestamp: November 17, 2022, 06:45:48 am
content: As many has mentioned, the vias is probably the cause.

author: michelvachon
author_rank: Newbie
timestamp: November 18, 2022, 02:18:17 am
content: regarding vias,I tested everything with a piece of paper between the pcb and the module,preventing all pads and vias from touching the module except for the VCC and ground pads.I attached the schematic, the PCB is a generic board made to fit multiple projects.The other side of the pcb can fit another 51822 in a different form factor.That's what the U66 and U225 components are.

author: thm_w
author_rank: Super Contributor
timestamp: November 18, 2022, 11:42:24 pm
content: I assume U100 is not mic5239-5.0, because thats a 5V regulator not 3.3V, right?I can't seem to find documentation for how this board should be connected, but it does look right. Maybe an issue with counterfeit NRF51822's?

author: michelvachon
author_rank: Newbie
timestamp: November 22, 2022, 01:29:05 am
content: it's not a mic5239, I just selected the first component that matched some other component's footprint.Question:Is is normal that the resistance decreases like that?Is a short the only explanation?The bare PCB without anything soldered on read >15Megaohms between vcc and ground.The capacitance changes a bit too, goes from 2.5uF to 3.5uF. Normal?

author: thm_w
author_rank: Super Contributor
timestamp: November 23, 2022, 12:35:58 am
content: "the resistance between ground and VCC is around 2.5 megaohms but after soldering, it sometimes decreases to 50kOhms"I mean its a normal value. But, if you are saying Vcc to Gnd is 2.5M on the module and >15M on the PCB, and then you solder to the PCB, without any components, and then it drops to 50k, then that is a bit odd.Of course if you start adding in components, like the regulator, etc. its going to affect Vcc to Gnd resistance.Capacitance changing with heat is normal, but, you are using an iron, the heat should not reach the capacitors much.

author: michelvachon
author_rank: Newbie
timestamp: November 25, 2022, 05:19:01 pm
content: Could my issue be caused by the solder type? Lead or no lead? Flux? Pcb finish? Solder gun temp?

author: thm_w
author_rank: Super Contributor
timestamp: November 25, 2022, 11:30:56 pm
content: Solder type, no.Flux, possible, if it was not a "no-clean" type, and then you didn't clean it after.PCB finish, no.Solder temp, unlikely, as I said you just touched the edge of the PCB and nothing else.

author: michelvachon
author_rank: Newbie
timestamp: November 29, 2022, 01:20:48 am
content: I never tried no-clean flux.I use that regular dark yellow MG Chemicals flux.Picture attached.I tested soldering the module detached from the PCB.This seems to work.Maybe because I was able to clean the flux properly.Picture attached.So I ordered no-clean flux, will try it out.

author: thm_w
author_rank: Super Contributor
timestamp: November 29, 2022, 10:15:21 pm
content: Yes if you read the datasheet:https://www.mgchemicals.com/downloads/tds/tds-8342-l.pdfThey state that cleaning is required. If a flux is not specifically advertised as "no-clean", assume it requires cleaning.It could be that or the standoff height you added. Which also means the other castellations have not chance of touching (if there was a PCB error).

author: michelvachon
author_rank: Newbie
timestamp: December 02, 2022, 12:44:09 am
content: Looks like the flux was the problem.I was able to solder that 51822 on my pcb and no issues so far.That's such a relief!This might explain some weird behaviour I had in the past with esp32 modules.Thanks for your time and help thm_w!