Re: [OT] surface mount components

Tony Fleming
 

Great detail information Bob!
Thank you.

On Thu, May 16, 2019 at 11:51 AM Bob Albert via Groups.Io <bob91343=
yahoo.com@groups.io> wrote:

I would only use glue if other methods seem inadequate. It's a foreign
material that may cause long term problems. Not sure about that. That's
why I wouldn't use crazy glue or epoxy. The latter is so tenacious that
later repair may be difficult. So acrylic cement seems to be a good choice.
Frankly, I prefer the clamp method. It leaves no residue. As for having
the part orient itself, sometimes that doesn't work and you have a mess on
your hands. Heating all terminals simultaneously can be challenging also,
requiring special tools and good dexterity.
I always worry about overheating the part. So I try to work quickly
without rushing so as to minimize thermal stress.
ChipQuik has some products that can be useful but their stuff isn't
cheap. I try to get along without it because I don't do these things often
enough to justify having that around.
In the final analysis, my most useful tools are a fine tip soldering iron
for installation and, for removal of devices with several pins, hot air. I
have removed complex ICs, relays, connectors, and more with hot air. It
gets difficult if the part is through hole and bent over on the solder
side. Sometimes I lose patience and break a part while removing it,
thinking that surely it's hot enough. But wasn't. And my many years of
experience making cold solder joints makes me careful during installations.
There is no substitute for practice and experience. As the carpenter
says, measure twice and cut once. So don't assume anything, since each job
has quirks. A few moments of pondering how to do it is worth a lot.
Bob
On Thursday, May 16, 2019, 9:35:29 AM PDT, Glenn Little <
glennmaillist@...> wrote:

Crazy glue will not withstand soldering temperature.
When heated to soldering temperature, it gives off vapors that probably
are not good to breath.

IPC-SM-817A address adhesives for SM parts.
This document does not appear to be available unless bought from IPC.
One adhesive that claims that it is complaint is EPIBOND 7275-1 10CC EFD.
This is an epoxy and I suspect that all adhesives that should be used
will be epoxy based.

Glenn

On 5/16/2019 11:55 AM, Tony Fleming wrote:
Nice information for people who do not use SMD's very often.
Some people use Crazy Glue to hold the part down - just a small drop -
before soldering it.
Is there anyone who thinks that using glue is not a good idea?

On Thu, May 16, 2019 at 9:43 AM Chuck Harris <cfharris@...> wrote:

If you do the soldering right, heating all of the joints
at once, the surface tension of the solder will rotate the
part around into alignment.

One of the contracts we all have with Murphy relative to SMD
rework is that we must melt all of the solder joints at the
same time so that we can avoid introducing tensions in the
parts that can cause breakage. The issue is especially bad
with fragile leadless parts like SMD capacitors. If you see
a capacitor that is "tombstoned" (eg. one side higher than
the other) it is under stress.

-Chuck Harris

Bob Albert via Groups.Io wrote:
One method that works for me is a small C clamp. I put the part about
where I want it and clamp it lightly. Then I nudge it into the exact
spot
and do the soldering. It worked great when I repaired the HP generator;
the job looks as good as the original.
Of course, in the middle of a large board you can't do this. What also
may work is a dab of plastic acrylic cement. While it's liquid you can
use
it to hold parts where you like. Then nudge a bit while it starts to
set.
If the clamp's jaws are too large you can put a bit of metal or plastic
between them and the part to improve access for soldering. Or just put
it
off center and solder one side of the part; once you do that it will
stay
in place while you do the other side.
For repairs it's usually enough to use residual solder. For fresh
installation you need to add some, of course. In the latter case,
solder
the board before you install the part and then you can clean up any
bridges. Once done, you can treat it as a repair.
These little ideas can be adapted to your own situation and dexterity
and tools.
Bob
On Wednesday, May 15, 2019, 8:10:15 AM PDT, John Griessen <
john@...> wrote:
On 5/15/19 6:26 AM, David Kuhn wrote:
Then
there is the sticky tweezers. They fustrate me too. Lately, I have
to
clean them with ISO to keep the parts from sticking from them.
I have these antimagnetic and anti static tweezers for sale that work
well
and can be hand formed to accept large objects:

https://www.ecosensory.com/tek/tweezers-1.jpg
https://www.ecosensory.com/tek/tweezers-2.jpg

Contact off list if interested.








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