We wouldn't need spacers and screws and lock washers. Mount those boards with magnets.
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8 years ago
filling vias
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8 years ago
You can (could?) buy "track pins". We used to use them in olden tymes when we were too cheap to buy PTH boards! :)
-- John Devereux
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8 years ago
Has anyone filled vias with solder to improve thermal and electrical conduction?
I figure that if a via has an unmasked pad, and it's solder pasted and reflowed, the solder will melt and flow into the via, partially or completely plugging it with solder.
Maybe arrange for 2x the paste that would fill the via volume?
I found this online:
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which seems to contain a lot of nonsense.
Seems to me that plugging a via with solder will radically reduce its resistances, and that lots of small vias are better than one big one.
The standard of the industry is DuPont's CB100. Used it for years.
Cheers, Harry
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8 years ago
The data sheet says "high thermal conductivity" but I can't see an actual value.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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8 years ago
The data sheet says "high thermal conductivity" but I can't see an actual value.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com John, this is a great place for you to test this stuff and use your FLIR gun. Lay out a small PCB, 100 A terminals, lots of traces with vias, filled and unfilled. I have been using CB100 for vias in pads, thermal vias, high current vias and vias. Try to keep aspect ratio (H/D) to about 6:1. makes my customers think that I am trying and gives me a good night's sleep. It's funny, when you pick up an 8 layer PCB with 2-4 oz layers and 6-2 oz layers and all vias filled, you instantly say, its heavy and it is cold. Regards, Harry
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8 years ago
[snip]
I worked for a company that did that to one of it products; a grid of plated holes under a high power SMD. The paste was expected to fill a certain percentage of the holes, otherwise the assemblers had fill up the difference.
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8 years ago
John, this is a great place for you to test this stuff and use your FLIR gun. Lay out a small PCB, 100 A terminals, lots of traces with vias, filled and unfilled. I have been using CB100 for vias in pads, thermal vias, high current vias and vias. Try to keep aspect ratio (H/D) to about 6:1. makes my customers think that I am trying and gives me a good night's sleep. It's funny, when you pick up an 8 layer PCB with 2-4 oz layers and 6-2 oz layers and all vias filled, you instantly say, its heavy and it is cold.
Regards, Harry
If I use unfilled vias with fixed-thickness plating, it makes sense to use lots of small vias. If they are filled with this stuff, they can be large with no big penalty.
Do you have a board house fill the vias with the DuPont stuff?
Maybe I'll bug them for a sample. I have a couple of thermal test boards that use resistors as the heaters.
I've heard of epoxy being used as a thermal via fill, but I suspect the DuPont is better.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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- posted
8 years ago
John, this is a great place for you to test this stuff and use your FLIR gun. Lay out a small PCB, 100 A terminals, lots of traces with vias, filled and unfilled. I have been using CB100 for vias in pads, thermal vias, high current vias and vias. Try to keep aspect ratio (H/D) to about 6:1. makes my customers think that I am trying and gives me a good night's sleep. It's funny, when you pick up an 8 layer PCB with 2-4 oz layers and 6-2 oz layers and all vias filled, you instantly say, its heavy and it is cold.
Regards, Harry
If I use unfilled vias with fixed-thickness plating, it makes sense to use lots of small vias. If they are filled with this stuff, they can be large with no big penalty.
Do you have a board house fill the vias with the DuPont stuff?
Maybe I'll bug them for a sample. I have a couple of thermal test boards that use resistors as the heaters.
I've heard of epoxy being used as a thermal via fill, but I suspect the DuPont is better.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com I believe that most board houses will do the CB100 trick. Some prefer the non conductive stuff, with a better COE to FR-4 but stick to your guns. regards, Harry
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8 years ago
The devil is in the details. Yes, filled vias conduct heat and electricity better than non-filled, but how much better? Is it worth the added cost/effort. "Lots of small vias" will be better than one big one... if there are enough of them. Design guidelines set minimum spacings. I think if you pack them at the minimum spacing the large ones will be better... if they have the same conductivity. Fill them with copper and you'll do better with larger ones as you have less space wasted by separation. For solder filled vias there will be an optimum size based on the tradeoff between density and conductivity.
-- Rick
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8 years ago
Unless they're plugged, and then, how. Remember also that a lot of vias, concentrated in one area, can make big holes in planes. Sometimes it's better to use larger and fewer holes so the keepouts/doughnuts don't overlap. One of my design review checklist items is looking for big holes or slots in planes caused by vias. I often find them where no one was expecting them.