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Hi Kjell,<br>
<br>
What problems have you had with leaving solder paste around on a
board a long time? I haven't experienced any, but I haven't on
purpose left it sitting out for a long time. I have left the solder
paste sitting out for weeks without any problems. Also, you can do
multiple re-flows if needed, but you have to cut your stencil up. I
can't make anything half as nice as the re-flowed solder connections
by hand. We use homemade stencils that are made on an LPKF
engraving machine. You can see a couple of videos of my student
using an ordinary toaster oven <a
href="http://www.youtube.com/watch?v=TCWVUdBO0kg">here</a>.<br>
<br>
I think we need to make these techniques more well known so that
more people will attempt and succeed on home made boards.<br>
<br>
73,<br>
<br>
Rob<br>
KL7NA<br>
<br>
On 03/08/2012 02:58 PM, Kjell Karlsen wrote:
<blockquote cite="mid:op.wavje9avnknqug@kjell-pc.lan" type="cite">*****
High Performance Software Defined Radio Discussion List ***** <br>
<br>
Hi Roland. <br>
<br>
The "best" solution is to use a reflow oven but there is one
drawback: The method to apply the solder paste is very important.
In my opinion the only way to do it properly is by using a Laser
Stencil but then you run into another problem: You have to place
all components on the PCB before it goes into the oven. It takes
too long time to do this as the paste dries too fast. You do not
have much more than one hour available and that is to short time
for all the components. It is possible to use the stencil and
apply paste only on the IC´s and other difficult components and
solder only those in the oven. Afterwards it is easy to install
the rest manually one by one. <br>
<br>
I have a reasonable priced hot air soldering station (AOYUE
Int2738) and a Quartz Infared Pre-heating Station (AOYUE INT853A).
You find one vendor in England. You must also buy the right
nozzles for the IC´s but they have all in stock. I start to place
all the IC´s correctly and solder 2 pins diagonally. When I am
sure they are correctly placed, i apply a narrow row of paste
along the pins on all sides. Use very little of paste but it is
easy to remove the excess solder afterwards using a dry, clean
soldering iron or a narrow solder wick. Be careful so no paste
gets under the IC. When all the IC´s are in place put the PCB on
the pre-heater, set it to 250 deg.C and wait until this
temperature is reached (after 1,5-3 min). Then use the hot air
tool to heat each component until you see the solder melt. It is
best to do some training on a scrap PCB and old IC´s. I did some
practices on old PC cards (Old VGA and Audio cards are fine) first
by removing the IC´s and then solder them back. I use the
pre-heater also to remove the parts. <br>
<br>
In fact there are only a few of the components on Hermes (LTC2208
and LTC6400) that are difficult to solder manually using only a
soldering iron with a narrow tip (0,4 mm). I have found that it is
easier to get good results when using higher temperatures than
normally advised (350 deg.C) and I also prefer a small 80W iron
(Weller WSP 80 or equivalent). With this the soldering process
goes much faster and also introduce less stress to the components.
The tip must be kept clean all the time and DO NOT USE LEAD LESS
SOLDER! In my opinion it is a disaster. <br>
<br>
One tip when using Solder Wick to remove excess solder: Apply
fresh flux to the wick before use, it is much more efficient then.
<br>
<br>
I have built 2 Hermes Beta that has been in use for nearly 2 years
and at least one of them will be dismantled and the expensive
components installed on a new PCB. I may keep one just for fun but
I do not think the software for the USB version will be updated. <br>
<br>
Enjoy the work and I hope to meet you on the band with Hermes in
both ends! <br>
<br>
73, Kjell <br>
<br>
<br>
<br>
<br>
<br>
<br>
På Thu, 08 Mar 2012 21:45:24 +0100, skrev roland etienne <a
class="moz-txt-link-rfc2396E"
href="mailto:roland.etienne@free.fr"><roland.etienne@free.fr></a>:
<br>
<br>
<blockquote type="cite">Hi, <br>
I’ve been lucky to get an Hermes PCB, and I am now collecting
all the components. I am wondering what is your favourite method
to solder all the ICs and oscillators: iron, hot air or refusion
oven ? <br>
Surely, I will buy an hot air station, any model recommended ? <br>
I would like to make some test with a refusion oven, any advice?
Is it possible to do several passes ? <br>
Thanks for any comments, <br>
73, Roland F8CHK <br>
</blockquote>
<br>
<br>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Rob Frohne, Ph.D., P.E.
E.F. Cross School of Engineering
Walla Walla University
100 SW 4th Street
College Place, WA 99324
(509) 527-2075 <a class="moz-txt-link-freetext" href="http://people.wallawalla.edu/%7Erob.frohne">http://people.wallawalla.edu/~rob.frohne</a>
</pre>
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