stm32f103c8t6 short cuts after programming!

[HSaee.1]

Hi, I am trying to make a circuit with stm32f103c8t6 and a nrf24l0+. I attach my schematic if pcb layout needed tell me to upload that. One of the circuit work good ( the send one) the other one which is identical does not.

after soldering I did check if any short cuts happen there was not any short cut, everything was good but after I power it up and connect the stlink_v2 and programming it ( it did it just fine) I tried to work with but it act abnormal

(especially timings) after I check for vcc and gnd pin I get 124 ohm or lower impedance on them I did it with other PCBs too but same thing happens.

My regulator , regulate voltage on 3.3 volt.

st_link_v2 work I could even program this 124 ohm stm32f103c8t6.

In other PCBs impedance reduce to 20 ohm.

The files are for altium designer .

send works but revive act abnormal .

[HSaee.1]

Hi , my problem is not impedance , now I have 50 ohm impedance but in this impedance the mcu could not connect to st_link or it connect (in higher impedance time change it)!but could not program and say protection mode is enable ( i did not enable it before!) and some time get program but hang during the short period of time. only different thing between the boards that works ( send is work! and my other board) and the one that's not work is this impedance.

first i did power up the mcu with st_link and then think maybe it could not give me that 27mA or more current because of that I connect it to better source (it could give 5A linear output) it programmed but mcu hanged after some time!

it's make no different when I push the reset button but in one case it's drop the current that mcu take from source. ( when it hang no different i should wait!)

Interesting thing is that when mcu hang I could not inter programming mode ( I mean connect to it and in here impedance is 120 ohm) but after some time ( after cutting the power) the impedance return to its 1k or more and then I could connect to it.

Make long story short the only strange thing I could see is impedance!

excuse me for writing much I want to describe all the situation.:\

[HSaee.1]

Hi , of course I cut the power ( base on Tevenan and Norton ( I do not know the right dictation ) that rule for calculating the

equivalent resistor and voltage ...).

And I do the measurement with my multi-meter.

[HSaee.1]

Hi, again I did the design for stm32f030k6t6 in this case after some time it hang and it does not work after several programing I could not even erase it .

sth should wrong with my design but I could not figure it out I attach my schematic.

[HSaee.1]

there is same problem with stm32f103c8t6 I get the new pcb and MCU but again same problem short circuit!

someone PLEASE help me!

[Piranha]

Another idea - probably all of these are consequences of using low-power modes, not configuring DBGMCU_CR and not using "connect under reset" on a debugger.

[HSaee.1]

Hi , again I program my MCU under reset mode but for DBGMCU_CR I am not sure even I know what is that I will read about and report in here.

But yes the under reset programming was a problem before but not now I did have problem with that too but in other project that I learn about alot.

THANK YOU FOR RESPOND

[HSaee.1]

Hi, I found the problem It was about footprint.

I downloaded a footprint from snapeda which was not approved ​and it got square pads.

In square pads sharp edge will be a problem and especially when frequency get higher and higher l. In 72MHz stm32 enter some situation to protect ic from this and show short circuit on it's power rail.

I replace footprint with a footprint which contain round pads and no more short circuit.

I almost change every thing in pcb the chip the solder and way of soldering nothing work except changing footprint.​

[HSaee.1]

I know it is long time ago but I could find my problem and fix them.

--First thing that is IMPORTANT is to use foot print with round and longer pad it could help you to solder the MCU better and easier.

--Second THING do not afraid high temperature put the iron on 400c or 380c and make sure you use good solder wire (It should melts in lower degrees) for avoiding heat damage to MCU do not keep iron more than a second on a pad if it did not soldered do the process again but do not keep it on MCU pin for long period of time. the purpose of 380c and 400c is that in the temperature on the tip of the iron is less than that number on screen and tip it self have some resistance again heat transformation and pcb itself will absorbs the heat all of this will cause

the COLD JUNCTION (which was my problem) and it will be pain.

--At last Use the flux ( that oil thing helping to solder to stick to pad) and carefully clean it after you done. and make sure all the pin (specifically GND and VCC) are connected .

[TDK]

> In square pads sharp edge will be a problem and especially when frequency get higher and higher

Nothing in the MCU operates at such a speed where this is a concern.

Bad workmanship leads to short circuits, not square pads.

[HSaee.1]

Yes, you are right. I updated my answer after, in my last answer I explained that the round pads will help us to soldering this happen a lot to me not just in ST MCU also in Texas Instruments DSPs that one power rail left open and not soldered properly and after some small period of working with them they just show short on power rail and from my side it always solved with soldering them again and pay attention to do it right.

Based on my experience (which is not much but worked for me) in design round pads do better in accepting solder so I suggest them.

Regards:*