Laying PCB in plastic box caused ESD damage? - Page 1
Forum section: electronics / beginners

author: Faringdon
author_rank: Super Contributor
timestamp: December 17, 2022, 10:50:07 pm
content: Hi,We have been testing a PCB with an LTC3786 on its bottom surface.Input is 18A so we made a platform so the wires to the PCB could be shorter.The platform was the attached two resistor boxes.....the LTC3786 would have been in contact with them, as it is on the underside.Also, the BSC027N04LS FETs are on the bottom.Do you think these boxes can cause ESD damage?...nobody remembers where they are from or if they have a datasheet.The PCB is a Boost SMPS, 5VIN, 24vout, 3.75A out, 350kHz. Synchronous Boost.LTC3786https://www.analog.com/en/products/ltc3786.htmlBSC027N04LShttps://www.infineon.com/dgdl/Infineon-BSC027N04LS%20G-DataSheet-v02_00-EN.pdf?fileId=db3a30431689f4420116c4323646080c

author: Gyro
author_rank: Super Contributor
timestamp: December 17, 2022, 11:31:45 pm
content: What else can I blame?https://www.eevblog.com/forum/manufacture/flux-remover-causes-esd-damage/

author: bidrohini
author_rank: Regular Contributor
timestamp: December 18, 2022, 07:30:46 am
content: No. Plastics are insulators.

author: Faringdon
author_rank: Super Contributor
timestamp: December 18, 2022, 09:58:04 am
content: because they are component boxes..albeit for resistors, we thought it may be special ESD plastic?They were bought years ago so no datasheet for them.I put myself on the "wrist strap ESD tester" with that box in my hand and contacting the metal ESD "button press piece", (instead of my finger tip) and get red instead of the normal green...so i guess that means they are ESD unsafe?

author: tggzzz
author_rank: Super Contributor
timestamp: December 18, 2022, 10:23:29 am
content: Quote from: Gyro on December 17, 2022, 11:31:45 pmHow could you possiblypossiblythink that?!Answer: by looking at these pages, paying more attention to the linkswithoutan "Re:" in them.https://www.eevblog.com/forum/profile/?area=showposts;u=776359https://www.eevblog.com/forum/profile/?area=showposts;u=139928(which is the only result when searching for "treez")

author: Kasper
author_rank: Frequent Contributor
timestamp: December 18, 2022, 05:12:34 pm
content: You could try this:https://www.mgchemicals.com/products/conductive-paint/esd-safe-coatings/esd-spray-paint/

author: Kasper
author_rank: Frequent Contributor
timestamp: December 18, 2022, 05:14:50 pm
content: While you're here, it'd be nice to follow up on this one:https://www.eevblog.com/forum/chat/giving-away-secrets-of-electronics/50/

author: EPAIII
author_rank: Super Contributor
timestamp: December 19, 2022, 03:41:05 am
content: Not necessarily. I have seen a cross talk problem in an audio device which was traced to the use of a conductive plastic used to construct the In/Out terminal board. The black plastic was colored black with carbon powder.Quote from: bidrohini on December 18, 2022, 07:30:46 am

author: Tomorokoshi
author_rank: Super Contributor
timestamp: December 19, 2022, 03:58:53 am
content: Quote from: EPAIII on December 19, 2022, 03:41:05 amAdding to this, insulating plastics are involved with ESD precisely because they are insulators. This is what allows a charge to collect on the surface. Consider the action of a polyester fleece across another fabric. Some action that could charge the surface could then be followed by another action that discharges the surface through the circuit board. This is why dissipative mats with wrist straps are necessary for sensitive electronics.Filler materials as noted above can make plastics "conductive". In this case, a lot of filler is added. A voltage in the range of 250 VAC would allow high enough current to flow to melt or burn the plastic. Alternatively, a dissipative fill for a high resistivity is enough to conduct away static charges without being a significant conductor at voltages in the range of 250 VAC. This is the level of an anti-ESD mat, black conductive plastic or cardboard containers, etc.Note that the pink foam or bags are not really static dissipating, but they do prevent the generation and accumulation of static charge. Otherwise the metallized anti-ESD bags the best for protection.

author: EPAIII
author_rank: Super Contributor
timestamp: December 19, 2022, 04:10:03 am
content: 1. You don't say what package the LTC3786 is in. But with the LTC3786 mounted on the bottom of the PCB, it is unlikely that any of the pins came into contact with the box no matter which package. The only way that could happen would be from the traces themselves or through other components mounted on the bottom.2. If the plastic was conductive, then that would work to PREVENT ESD damage. Conductive plastics are only moderately conductive. They will exhibit a moderate amount of resistance. So any flow of current would be restrained to a moderate level and damage would probably be averted. This is why grounded, conductive mats are used on workbenches.3. Over 45 years of handling electronic components tells me that ESD damage is rare and difficult to achieve. I have handled many thousands of parts and never, ever had one damaged in this manner.The above three reasons make me believe that almost every other possible reason for the circuit to fail is a lot more likely than ESD damage. I am sure it does happen, but I think you must try really hard to make it happen.If the circuit was under power when it contacted the box, then the box, if it is conductive, could have shorted the circuit and that could have caused damage.Quote from: Faringdon on December 17, 2022, 10:50:07 pm