Electrical Over Stress - Looking your assistance to resolve the EOS issue in Automotive ECU

[Ganesan Magizh]

Dear Friends,

I am working in an Electronics Manufacturer service (EMS) and we do PCB assemblies for Automotive products (ABS).

We are getting many field failures due to components burnt issue. Mostly like diodes, ASIC, MCU and FET components are getting damaged/burning in the field.

Whenever we are sending the defective parts to components supplier for analysis the result from them always is ELectrial Over Stress (EOS).

We have ESD protected manufacturing area and following the ESD standard during the manufacturing process and we ensured that the solderability of the PCBA is good.

I would like to know the possible cause of EOS. Please share your experience and suggestion on EOS.

Thanks in Advance.

Ganesan

 

[rjenkinsgb]

If they are field failures rather than testing, it's not necessarily a problem during assembly.

What voltage ratings are your assemblies designed to tolerate?
Anything for use on a nominally 12V automotive system should be rated for an absolute minimum of 60V spikes or surges on any terminal without damage, if I remember correctly.

 

[unclejed613]

there are a few possibilities here, 1) whatever vehicle(s) your product is going into may have a problem in the charging system that causes overvoltage conditions on a regular basis. 2) you need to beef up (or add) protection circuits and and TVS devices (Transient Voltage Suppression) to your products (this would also help mitigate problem #1 somewhat) 3) check the integrity of the circuit grounds in your equipment, especially for the voltage regulators that feed low voltage devices like the MCU and other logic. an open ground on a regulator will feed the whole unregulated voltage to the low voltage parts. all grounds should be connected together on the circuit board itself, so that any corrosion or loose screws, etc will not lift any grounds on the circuit board.

by the way, overkill is one way of improving reliability. if the device is running off of 12V, it's hard to go wrong by using components rated for 60V.

 

[The March Muppet]

overkill is one way of improving reliability. if the device is running off of 12V, it's hard to go wrong by using components rated for 60V.

Yup. Of course the polar opposite to the "build to cost" theory of SAE engineering.

Is the same specific component giving up the ghost in a given production run?

It's either trying to do too much work (overcurrent, pulse width), giving up the smoke (insufficient thermal mitigation), or taking the nondescript A train to silicon hell (unforeseen junction voltages in either direction - watch particularly for solenoid back EMF)

 

[picbits]

When I used to design and build stuff for cars, approx 70% of the parts and cost of the devices were to make them as immunue to both spikes and noise on the automotive system as well as idiot proofing them as much as possible from being incorrectly installed.

Load dumps, transients, reverse charging of the battery to name but a few. Out of the few hundred units sold, I only had one unit fail in the field which was due to the customer putting the bare PCB on top of a metal engine cover .....