B
Bill Sloman
Guest
On Tuesday, February 25, 2020 at 2:17:06 AM UTC+11, jla...@highlandsniptechnology.com wrote:
https://en.wikipedia.org/wiki/Thixotropy
John Larkin hasn't posted his definition. In fact thixotropic materials have variable viscosity, which can be decreased by putting a high shear stress on the material, forcing it to flow, after which the viscosity increases with time.
You have to force them to flow, but once you have forced them into some new shape they will tend to stick with it.
--
Bill Sloman, Sydney
On Mon, 24 Feb 2020 09:09:52 -0500, Joe Gwinn <joegwinn@comcast.net
wrote:
On Sun, 23 Feb 2020 10:16:11 -0800, jlarkin@highlandsniptechnology.com
wrote:
On Sun, 23 Feb 2020 12:03:11 -0500, Joe Gwinn <joegwinn@comcast.net
wrote:
On Fri, 21 Feb 2020 12:54:45 -0800, John Larkin
jlarkin@highland_atwork_technology.com> wrote:
On Fri, 21 Feb 2020 20:28:19 +0000, David Nadlinger
david@klickverbot.at> wrote:
On 21.02.20 7:50 pm, John Larkin wrote:
Here's a pulse generator output stage, as a mouse-bite component.
https://www.dropbox.com/s/w9ax8q9u00obnx4/T577_Glob_2.jpg?raw=1
Is that epoxy top for mechanical robustness of some (presumably GaN)
chip, or just for IP protection reasons?
â David
Both. I'm using EPC BGA GaN fets, and they are very fragile. A tiny
bump can knock them off the board, or fracture the chip. They are like
little glass blocks with sharp corners.
We need better epoxy, higher viscosity to cover all the parts, and a
nice way to dispense in production. Maybe a pump nozzle on our Tormach
n/c mill?
It sounds to me like you need a thixotropic epoxy mix. Liquifies when
pumped, then stiffens up so it won't drool off the board.
.<https://www.masterbond.com/properties/thixotropic-adhesives
Joe Gwinn
I remember bad experiences with Master Bond. How are they these days?
They want me to register by filling out forms. No direct email
address. What a nuisance.
I think I want a liquid but high viscosity epoxy. Thixotropic might
not flow into nooks and crannies, and wouldn't look nice and shiny.
Everybody makes the thixotropic epoxy, and all viscosities are
available, not just the pasty stuff shown in the ad. So I'd ask
around.
By definition, thixotropics don't flow. Like mayonaise.
https://en.wikipedia.org/wiki/Thixotropy
John Larkin hasn't posted his definition. In fact thixotropic materials have variable viscosity, which can be decreased by putting a high shear stress on the material, forcing it to flow, after which the viscosity increases with time.
You have to force them to flow, but once you have forced them into some new shape they will tend to stick with it.
--
Bill Sloman, Sydney