Electronics > Projects, Designs, and Technical Stuff
What´s the purpose of the white gunk?
aduinstat:
--- Quote from: arildj78 on December 07, 2022, 05:21:49 am ---Does gunk have a real name and a part number at DigiKey?
--- End quote ---
RTV162 is what all the assemblers I talked to use. It's kinda expensive though.
T3sl4co1l:
So in summary:
- Strain relief for the bulky component.
- But the material is most likely too soft to do anything.
I'd say it's an erroneous choice by the assembler or designer. Epoxy, superglue or other more rigid substance would be fine though.
--- Quote from: Siwastaja on December 07, 2022, 04:25:11 pm ---When SMD parts need added mechanical support, one usually sees one of the two:
1) underfill for parts like BGA packages, this is thin polymer fluid which is applied after assembly right next to the component and flows by capillary action into the small gap, totally filling the voids between the component and PCB, and then is cured using heat
2) glue which is applied to the board by a CNC dispenser in small dots, before pick&place, which is cured during reflow.
Both are almost impossible to see from the finished board.
--- End quote ---
I've seen a hybrid approach: red gunk squirted liberally around the corners of the (BGA) chip, of firm consistency -- possibly component glue itself, just put on much thicker than the tiny dab you'd use underneath small chip components. (I don't think the same chip was underfilled, but I'm not sure; I didn't try to remove it or anything.)
Tim
TimNJ:
We use tons of electronics RTV at work...it does work. e.g. Plenty of examples of shock & vibration tests which failed (transformers, inductors shearing their pins, transformers getting knocked right off the board (non-plated thru-holes worse offenders). Add RTV and largely is fixed.
Probably the key thing is using the right RTV. The stuff we use cures to almost a rubber tire hardness...well, maybe a little softer than that, but close.
I don't think using silicone RTV sealant from Home Depot is going to do very well. It's far too soft.
aduinstat:
--- Quote from: TimNJ on December 07, 2022, 11:58:38 pm ---We use tons of electronics RTV at work...it does work. e.g. Plenty of examples of shock & vibration tests which failed (transformers, inductors shearing their pins, transformers getting knocked right off the board (non-plated thru-holes worse offenders). Add RTV and largely is fixed.
Probably the key thing is using the right RTV. The stuff we use cures to almost a rubber tire hardness...well, maybe a little softer than that, but close.
I don't think using silicone RTV sealant from Home Depot is going to do very well. It's far too soft.
--- End quote ---
RTV from Home Depot will release acetic acid as it cures and corrode your components.
wraper:
--- Quote from: aduinstat on December 08, 2022, 12:14:12 am ---
--- Quote from: TimNJ on December 07, 2022, 11:58:38 pm ---We use tons of electronics RTV at work...it does work. e.g. Plenty of examples of shock & vibration tests which failed (transformers, inductors shearing their pins, transformers getting knocked right off the board (non-plated thru-holes worse offenders). Add RTV and largely is fixed.
Probably the key thing is using the right RTV. The stuff we use cures to almost a rubber tire hardness...well, maybe a little softer than that, but close.
I don't think using silicone RTV sealant from Home Depot is going to do very well. It's far too soft.
--- End quote ---
RTV from Home Depot will release acetic acid as it cures and corrode your components.
--- End quote ---
It will not if you buy neutral cure stuff. However it's still would not be the best choice. Dielectric properties not rated, likely some anti-mold additives added. Likely too soft.
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