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[wxsig] hot glue follow-up

John Bennett jabennett at insightbb.com
Fri Jun 25 12:07:11 UTC 2010


The reader should understand that while there may be some heat stress 
associated with applying hot glue, it does not approach the heat stress 
that components and boards are subjected to when traveling through a 
solder wave machine or just simply using a soldering iron.

As to physical damage, in the Heath ID5001 weather station assembly of 
the humidity sensor, they used a conformal coating similar to the 
Dow-Corning products mentioned. The humidity sensor on that station had 
a life span of about 3-4 months at best. I routinely had to replaced 
those sensors (actually still have a handful left). Removing that 
conformal coating the first time was tedious and far more difficult than 
the hot-glue. The potential for damage was there as well.

What I'm trying to say is that you should not be afraid to use hot glue 
for fear of damaging anything. I feel the low risk involved far 
outweighs the advantages. That and hot-glue does not give off toxic 
fumes when applied as some conformal coatings do.

Gerald Creager wrote:
> There are several spray-on and paint-on conformal coatings (eg., 
> Dow-Corning 3140, 3145) that are less likely to thermally stress 
> components or traces, or provide a mechanical damage potential upon 
> removal, than hot glue. That said, this is certainly a testimony to 
> adequately protecting exposed PCB traces and should be taken to heart!
> 
> gerry
> 
> John Bennett wrote:
>> About three years ago I installed a T-238 station with the X1W-1, 
>> X1W-2 and X1W-4 kits. The rain gauge option had been installed on the 
>> X1W-2 (outdoor temp/humidity). It has been intermittent for some time 
>> and finally stopped working.
>>
>> I had wrongly assumed that the counter chip had been fried. After 
>> determining the DS2423 was OK, I checked the opto-isolator to find 
>> that Vcc was missing on pin one. It did not take long to find the 
>> problem. Part of a trace had corroded away. The part that had vanished 
>> was not covered with hot glue. The only protection was the solder mask 
>> on the PC board itself. Moral of the story here is that all traces 
>> pads, pins, etc. that are exposed must be somehow sealed. Just be 
>> certain to follow the guidelines I gave on applying the glue in the 
>> manual.
>>
>> As a point of interest, only the bottom of the board had corrosion 
>> problems. The board was installed in a Davis radiation shield and 
>> therefore was facing down. Apparently moisture with some contaminants 
>> routinely collects on bottom of the board which is facing up. The top 
>> of the board which faces down showed virtually no signs of corrosion.
>>
>> In the process of trouble-shooting, it was necessary to peel away some 
>> of the hot glue. This was not an easy task, but when I did get if off, 
>> ICs, board, traces - virtually all components looked as if they had 
>> just been installed. No mold, dirt, peeled off paint or solder mask. 
>> Hot glue works. It just doesn't look pretty.
>>
>> 73,
>> John Bennett, N4XI
>>
>>
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> 



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