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Paste!

Paste!

2005-11-29 by Mike Young

They shipped it by UPS-slow-boat-via-Panama-Canal, I think. Oregon to
Chicago in 8 days. It took Lewis and Clark at least 20 times that long, so
why am I complaining?

I made a few small dabs on a quickie board, shoved an SO14 into the midst of
it, and cranked up a medium flame under a flat bottom skillet. It turned
ugly gray like Stefan said it would. I nodded to myself, and waited. A
couple of minutes later, the gray turned shiny silvery. "Pretty!" says I.
And it is, except I can make the dabs much (much, much) smaller in the
future. Low flame, too, in the future. It seemed to cook awfully fast, about
ten minutes from flame on to "Pretty!".

The skillet has a couple of copper ears for handles. Nobody uses it for
cooking beyond their first experience, at least. It burns your hand even
through oven mitts. For timing a slow cool-down, though, what can be better?

I should've done this years ago. All 14 pins are dead center on their pads
(even though I couldn't see them after I mushed it in). No contortions, no
pinning, no painful tweezing. Ya gotta love it. Best $20 I ever spent. Well,
maybe not. I'm sure it comes close, though.

Mike.

Re: [Homebrew_PCBs] Paste!

2005-11-30 by Stefan Trethan

On Wed, 30 Nov 2005 00:35:14 +0100, Mike Young <mikewhy@...>
wrote:

> It seemed to cook awfully fast, about
>
> ten minutes from flame on to "Pretty!".


That's not a terribly fast reflow. All profiles i've ever seen were under
300s, with most beeing preheat.
As long as you don't stay in the "really hot" temperature too long i guess
it is OK.

ST

Re: [Homebrew_PCBs] Paste!

2005-11-30 by Mike Young

"A watched board never reflows". I'll time it next time, and calibrate the
knob. I turned off the heat as soon as all pads "popped", and let it cool
undisturbed. That should be a usable profile as long as the ramp up isn't
too aggressive. I'm a little nervous now, with SMD caps going onto the next
board.

----- Original Message -----
From: "Stefan Trethan" <stefan_trethan@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Wednesday, November 30, 2005 2:37 AM
Subject: Re: [Homebrew_PCBs] Paste!


> On Wed, 30 Nov 2005 00:35:14 +0100, Mike Young <mikewhy@...>
> wrote:
>
>> It seemed to cook awfully fast, about
>>
>> ten minutes from flame on to "Pretty!".
>
>
> That's not a terribly fast reflow. All profiles i've ever seen were under
> 300s, with most beeing preheat.
> As long as you don't stay in the "really hot" temperature too long i guess
> it is OK.
>
> ST
>
>
>
> Be sure to visit the group home and check for new Links, Files, and
> Photos:
> http://groups.yahoo.com/group/Homebrew_PCBs
>
> If Files or Photos are running short of space, post them here:
> http://groups.yahoo.com/group/Homebrew_PCBs_Archives/
> Yahoo! Groups Links
>
>
>
>
>
>
>

Re: [Homebrew_PCBs] Paste!

2005-11-30 by Leon Heller

----- Original Message -----
From: "Mike Young" <mikewhy@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Wednesday, November 30, 2005 11:39 AM
Subject: Re: [Homebrew_PCBs] Paste!


> "A watched board never reflows". I'll time it next time, and calibrate the
> knob. I turned off the heat as soon as all pads "popped", and let it cool
> undisturbed. That should be a usable profile as long as the ramp up isn't
> too aggressive. I'm a little nervous now, with SMD caps going onto the
> next
> board.

I just tried a Weller Pyropen for mounting a QFN chip with solder paste I
got as a sample. I had trouble applying the solder paste, it wouldn't stick
properly, so I used too much in a couple of places. It worked fairly well,
although I'll have to clean up the excess solder blobs with some desoldering
braid. Perhaps I should have applied a little gel flux first to make the
pads sticky. That paste is probably intended for use with a stencil.

I've ordered a syringe of a different paste that is intended for manual
application. That should work a lot better.

Leon

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Re: [Homebrew_PCBs] Paste!

2005-11-30 by Stefan Trethan

On Wed, 30 Nov 2005 12:39:40 +0100, Mike Young <mikewhy@...>
wrote:

> "A watched board never reflows". I'll time it next time, and calibrate
> the
>
> knob. I turned off the heat as soon as all pads "popped", and let it cool
>
> undisturbed. That should be a usable profile as long as the ramp up isn't
>
> too aggressive. I'm a little nervous now, with SMD caps going onto the
> next
>
> board.


don't worry, they can take quite a beating.
If you need top reliability and stuff you need to stick to the recommended
profiles, but for homebrew stuff it is less critical.
Perhaps you have a multimeter with PC connection, or a storage scope, or a
x/y plotter, then you can record the profile.
Even so, with simple ovens you never get uniform temperature so it depends
where you measure etc...


ST