Custom pcb, W5500 chip dies, need help to figure out the reason

Question

Warning: long post. As part of a pcb, I have a W5500 circuit. As far as I know, I have followed all recommendations in the datasheet, the hardware guide, and other best practices (like advice given in thread in this very forum). However, for some reason, the W5500 chip dies. Sometimes it takes a while (I had one prototype pcb working for about a week before the W5500 died, another prototype lasted about a day) and sometimes it dies quickly. So I have been populating some prototype pcbs with only the W5500 circuit, and powering it with 3.3V directly from a lab power supply. It doesn’t help, the W5500 chip still dies. The W5500 part of the schematic is this W5500_21169×826 143 KB . I have also tried a minimal version of the W5500 circuit (basically just the two capacitors that the W5500 needs and the decoupling capacitors). Nope, the W5500 still dies. The minimal schematic is this W5500_31169×826 89.5 KB Component values are on the schematic, if anything is unclear, feel free to ask for more info. I hand solder the prototypes. The pcb is 4 layers, the stackup is top layer, ground plane, inner signal layer, bottom layer. The relevant parts of the pcb is shown in these pictures: top layer pcb_top_layer_Screenshot 2022-10-05 133921501×800 68.4 KB inner signal layer pcb_inner_signal_layer_Screenshot 2022-10-05 134043505×820 38 KB bottom layer pcb_bottom_layer_Screenshot 2022-10-05 134156512×824 64.6 KB I have verified the components (values, package size and other data), the footprints against the datasheet, the reference schematic and the wiz550io schematic and pcb. I have checked the gerber files for errors - none found. I have also had a couple of colleagues double check my work - they couldn’t find any issues either. I have verified that the pcb is ok - no shorts between 3.3V and ground, between pads or otherwise suspicious measurements. On the long surviving prototypes I measured the voltages (3.3V in, VDD digital and analog on the W5500) they are stable and within specifications. Symptoms: On the W5500 only or W5500 minimal only prototypes the symptoms are that current draw rises quickly to about 130 - 135 mA and sometime after that the W5500 chip dies. How do I know that the W5500 chip dies? I measure the resistance between 3.3V input and ground on a populated prototype pcb before applying power to it, it is in the kilo-ohm range. after the W5500 has dies, the measurement is just a few hundred ohms. If the W5500 chip is the desoldered, the measurement goes back to kilo-ohm range again. Obviously something must be wrong with my schematic or pcb layout, but so far we (my colleagues and I) haven’t been able to find it. Any advice would be great. Thanks.

Eugeny · Answer

Below is quick thoughts on the design, not related to the main problem: MMZ1005 is a ferrite bead for signal filtering, select another one for power filtering. In minimal configuration some very important components like EXRES1 resistor are required to keep PHY functioning properly. tingox: current draw rises quickly to about 130 - 135 mA and sometime after that the W5500 chip dies. Sounds like chip locks up. How fast it happens? Did you have an opportunity to see if it starts heating heavily? I see you still have SPI connected to the chip. What is going on there? I am not sure but generally some wrong command through SPI may get chip going crazy. Do not know if it is possible, why not!

Eugeny · Answer

Thanks for the info. How do you solder the chip in the first place? What is the soldering profile?

tingox · Answer

The prototypes are hand soldered. Soldering iron, microscope and steady hands.

tingox · Answer

Interesting, I keep the soldering iron at 370 degrees Centigrade (lead free solder you know). I could try preheating the pcb (we have a hot plate, not ideal but it might work) and solder it at a lower temperature.

tingox · Answer

Hand soldered a prototype board using leaded solder at 315C. Unfortunately it didn’t help, the chip still dies. I use a lab power supply with a current limited output, increasing the current limit in steps for the testing. I use the minimal schematic, but added the EXRES1 resistor. Questions: the external components normally connected to the PHY lines on the chip are not fitted, could that kill the chip? will using a current limited power supply kill the chip?

tingox · Answer

/RESET pin has internal pullup, no other connection in minimal setup. In full setup, it is connected to the mikrokontroller. All components are ordered from trustworthy sources (Digikey / Mouser). I have ordered W5500 chips from both, in order to rule out a possible batch problem. I will measure resistance as soon as I can. I will look into if we can change the clock circuit.