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[wxsig] hot glue follow-up

Gerald Creager gerry.creager at tamu.edu
Fri Jun 25 03:13:56 UTC 2010


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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-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843



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