SN65HVD1050: Statically Induced Voltage

Hello Max,

Thanks for the quick response. Would/could you get ESD within the microchips themselves across the tiny layers of insulation or would it more likely discharge somewhere down stream on the PCB?

I apologize for the amateur questions, I am an hydraulics engineer and I'm trying to understand the mechanics behind the issue.

Joshua,

No problem asking questions - we are happy to try to help.

The flow of charge will favor lower-resistance paths. Typically what we are concerned with when we think of static discharge is a charged insulator coming into contact with (or becoming close enough in proximity to in order to create an arc) a conducting portion of a circuit (typically an external connector of a system or the pin of loose device while it is being handled). This can cause a large excursion in the voltage seen at the pin of a device, and most devices will try to limit this by activating a low-resistance clamp. Whichever component on the net that clamps first will take the brunt of the energy. Above a certain energy level, this clamping circuit may give out and cease to protect the rest of the chip (resulting in various kinds of damage). "Clamps first" typically means "clamps at a lower voltage," although for very fast transients the placement of the devices within the signal path may factor in as well.

Is this the kind of static discharge you are thinking of, or is there another coupling mechanism you have in mind?

Max

Max,

The PCB within which this chip resides is currently isolated from ground while in the presence of a 75 kV static electric field. The failed chips show evidence of burning within themselves, which is what prompted me to ask if the static discharge is happening within the chip itself or if there is an arc to ground somewhere downstream of the chip that is causing the damage due to momentary high current?

With my extremely limited knowledge of statically induced voltages, I didn't know if the internal potential within the chip caused by the static induction could cause the insulation in the chip to break down when the potential is high (75kV)?

Joshua,

Sorry, I might have misunderstood. Just to confirm - are you talking about static in the sense of charged ions flowing onto the board (in quantities high enough to create a 75 kV potential), or is the board itself in a "static" (constant) electric field? If the former, I wouldn't expect internal damage to occur since lower-resistance paths would exist outside the chip. If the latter, do you know what the field strength would be in V/m? How is the field generated? I've never seen damage caused by something like this; the dielectric strength of the insulation used in the chip would be significantly higher than that of air, so I would expect external arcing to occur before any internal damage. I don't want to to completely rule it out without understanding your set-up, though.

Max

Hello Max,

It is the latter. I do not know the field strength, but I do know that the field is generated by an electrostatic painting process. The process generates 75kV in order to maximize paint adherence. The field is more than likely not constant because the paint head is constantly moving thus generating an AC component superimposed onto the static 75kV DC field. I also imagine (correct me if I am wrong) that the DC field strength will increase as the paint head gets closer to the devise in question, since the electric field is where the paint particles are.

The PCB board that this chip is mounted to is fully encapsulated in potting material in an aluminum container which is attached to the vehicle chassis being painted. The vehicle chassis and everything on it are earth grounded via the harness in the paint booth. A wire harness is attached to the electrical connector on the aluminum container, but the other end is free and not connected to anything (big antenna). This effectively isolates the PCB board and the chip from earth ground allowing for the electric field to induce voltages onto it. We have inspected the potting material and have found no evidence of carbon tracks so I am fairly confident that we are not arcing from the board to the aluminum container through the potting. We have also not found any evidence of carbon tracks or burn marks elsewhere on the PCB board other than inside the CAN transceiver, which is why I thought that the arcing maybe occurring inside the microchip.

If we are constantly inducing and collapsing the 75kV voltage on board as the field strength varies (at the location of the PCB) with the movement of the paint head; can this constantly changing very high voltage (relatively) damage the transceiver, or does there need to be a discharge somewhere in order for damage to occur?

Hi Joshua,

I am a colleague of Max looking into your problem as well. Thank you for your detailed description, it helps us understand the application better. Am I correct in my understanding of your description that since the wiring harness is not connected to anything except the connector on the aluminum container, that this means the board is not powered and does not have any signals active during the painting process? I also want to make clear in my understanding that there is no common ground connection between the PCB and the aluminum box and vehicle chassis and that the PCB is mounted in an isolated way inside the box. Is the only connection to earth GND through the wiring harness that is disconnected? I believe I understand both of those to be true based upon your previous posts.

I have a couple of additional questions as well. You mentioned there was evidence of burning within themselves. Can you elaborate on this damage? Is there physical damage to the package of the transceiver such as deformation or discoloring of the plastic body and if so what does that look like and is it always in a specific location such as near a specific pin? Is it visible on the a device pin or pins and if so what does that look like? Or have you opened up the transceiver to literally look at damage "within" the transceiver?

Is damage occurring on every chassis that is painted, or what is the percentage of damaged units? At which point in the process did you notice the damage to the devices?

Are you inspecting the devices for damage immediately after the painting process before the wiring harness is connected to power and a signal source, or is it only after the wiring harness is energized that you are looking for damage? I am wondering if there could be some static stored charge that remains on the PCB, device, or wiring harness after the painting process is completed that could discharge at the moment the wiring harness is connected. Do you have a process for safely discharging any remaining static energy in the system following the process?

If the PCB is truly isolated from ground while in the presence of the 75kV static electric field, I am assuming that a charge would buildup on the components without a path to safely discharge. When the wiring harness is connected, it could then provide the first possible discharge path and cause all of the stored charge to discharge very quickly causing damage in the process. Could a very weak path to ground be created through something like a 1M resistor that would allow a safe and controlled path for the static buildup to discharge from the PCB and wiring harness when not in the presence of the static field, i.e. after the painting process is over?

Regards,
Jonathan

Hello Jon,

Yes you are right, the PCB board wire harness is only connected to the aluminum container and the devise is not powered during the painting process. Please reference the picture below for the wiring diagram. Yes you are correct in that the only direct connection from the PCB to earth ground is through the wire harness, but it is disconnected.

The burning that I was referencing was found inside the transceiver after the cover was removed. Please see below for pictures of the damage as well as an X-Ray and SAM inspection.

Damage is not seen on every chassis, the ratio of returned parts is low. These failures are infant failures with very low machine hours, but are not discovered in the manufacturing plant, even though they are powered and cycled after the paint process.

I am not aware of any safety procedure for discharging any elements after the painting process. I was under the impression that with induction, once the electric field is removed, any induced voltages go away? How can the induced voltage remain once the field collapses?