The amount of solder should be controlled by patterning the paste and the thickness of the stencil… You don’t want to whole pad with paste….
Cross hatch the solder paste avoiding the via holes… it will spread out and fill the pad but not the entire via barrel.
I know it’s touchy but it works.
☺
William Brooks, CID+
Printed Circuit Designer
2747 Loker Ave West
Carlsbad, CA 92010-6603
760-930-7212
Fax: 760.918.8332
Mobile: 760.216.0170
E-mail: [log in to unmask]<mailto:[log in to unmask]>
From: Tom Brendlinger [mailto:[log in to unmask]]
Sent: Saturday, January 07, 2017 7:16 AM
To: (Designers Council Forum) <[log in to unmask]<mailto:[log in to unmask]>>; Brooks, William <[log in to unmask]<mailto:[log in to unmask]>>
Subject: Re: [DC] Plugging Thermal Via Holes with Soldermask?
On the board I'm attempting to do this on, drill size is 8mil and we are seeing significant solder on the back of the board.
Anyone who is recommending the solution of just using very small vias- when you have had this work, did you use an especially viscous solder? Lead free or leaded? Any specific process issues that I might have missed?
Tom Brendlinger, CID
Electrical Engineer
Levant Power / ClearMotion
On Jan 6, 2017 12:35 PM, "Brooks, William" <[log in to unmask]<mailto:[log in to unmask]>> wrote:
It may be that you can do this without any mask at all.. The capillary action of the hole is dependent on the wicking of the solder and it’s surface tension and the weight of the column of solder might play into it… think of a syphon hose pulling gas out of the tank of your car… if the viscosity of the fluid is very thin, it may allow an air bubble to get in and disrupt the syphon effect…or flow freely if there is enough weight pulling on the fluid and air is prevented from interrupting the flow…
But, if it’s very thick viscosity like Ketchup it may be very hard to get it to flow without a lot of encouragement.
Seems like it takes some thick fluids forever to move… even long enough to pass through the reflow oven and not out the bottom of the via in the board…
Taping or plugging the via temporarily with removable mask will trap air or moisture in the hole… when you heat the board to solder, the air will expand and want to escape and if it can’t get out through the bottom of the board, it will get out under the part you are trying to solder through the solder paste and bubble out little balls of solder in the process which can roll around on the top surface and cause shorts… much like a volcano spewing out lava.
William Brooks, CID+
Printed Circuit Designer
2747 Loker Ave West
Carlsbad, CA 92010-6603
760-930-7212<tel:760-930-7212>
Fax: 760.918.8332<tel:760.918.8332>
Mobile: 760.216.0170<tel:760.216.0170>
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