Homebrew PCBs

Hi Guys,

I am looking at options for a project I have underway, 
which "unfortunately" requires me to solder a 100pin TQFP surface 
mount component to a PCB (yet to be designed). There appear to be 
various ways of doing this, but the one that I think I can manage is 
using a hot air pencil. I've seen various designs modifying 
desoldering tools but being in the UK they are quite expensive - 
certainly not as cheap as £9.99 from RadioShack! I have found one, 
from Rapid Electronics which is fairly priced at around £20, but it 
is an "inline" desolder, and I am uncertain if this could be 
modified. Likewise, there is no specified power output for it, so I 
am unsure as to its suitability.

The other option I thought of is perhaps using a portable gas 
soldering iron. Rapid again sell a 70W equivalent gas soldering iron 
with a hot air tip, and I wondered if anyone has tried one of these 
to see if it works?

My other concern is that I will be manufacturing the board using the 
Resources at my University, which are just like any other "school" 
PCB manufacturing tools using etching chemicals - am I likely to get 
the "resolution" needed for etching the pads onto the PCB for this 
component using the chemical etching process or will this also be 
problematic?

Many thanks for any help.
Chris

----- Original Message ----- 

From: "Chris Warnes" <warneschristopher@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Tuesday, January 20, 2004 3:33 PM
Subject: [Homebrew_PCBs] Gas Soldering Irons as hot-air pencils?


Hi Guys,

I am looking at options for a project I have underway,
which "unfortunately" requires me to solder a 100pin TQFP surface
mount component to a PCB (yet to be designed). There appear to be
various ways of doing this, but the one that I think I can manage is
using a hot air pencil. I've seen various designs modifying
desoldering tools but being in the UK they are quite expensive -
certainly not as cheap as \ufffd9.99 from RadioShack! I have found one,
from Rapid Electronics which is fairly priced at around \ufffd20, but it
is an "inline" desolder, and I am uncertain if this could be
modified. Likewise, there is no specified power output for it, so I
am unsure as to its suitability.

Another technique is to tack down the corners, apply plenty of liquid flux
and 'flood' the leads by dragging a blob of solder along them. Clean off the
excess solder with desolder braid and remake any suspect joints.

The other option I thought of is perhaps using a portable gas
soldering iron. Rapid again sell a 70W equivalent gas soldering iron
with a hot air tip, and I wondered if anyone has tried one of these
to see if it works?

My other concern is that I will be manufacturing the board using the
Resources at my University, which are just like any other "school"
PCB manufacturing tools using etching chemicals - am I likely to get
the "resolution" needed for etching the pads onto the PCB for this
component using the chemical etching process or will this also be
problematic?

If the lead spacing is 0.5 mm this could be tricky. 0.65 mm should be OK.



Leon Heller, G1HSM
Email: aqzf13@...
My low-cost Philips LPC210x ARM development system:
http://www.geocities.com/leon_heller/lpc2104.html

--- In Homebrew_PCBs@yahoogroups.com, "Leon Heller" 
<leon_heller@h...> wrote:
> 
> ----- Original Message ----- 
> From: "Chris Warnes" <warneschristopher@h...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Tuesday, January 20, 2004 3:33 PM
> Subject: [Homebrew_PCBs] Gas Soldering Irons as hot-air pencils?
> 
> 
> Hi Guys,
> 
> I am looking at options for a project I have underway,
> which "unfortunately" requires me to solder a 100pin TQFP surface
> mount component to a PCB (yet to be designed). There appear to be
> various ways of doing this, but the one that I think I can manage is
> using a hot air pencil. I've seen various designs modifying
> desoldering tools but being in the UK they are quite expensive -
> certainly not as cheap as £9.99 from RadioShack! I have found one,
> from Rapid Electronics which is fairly priced at around £20, but it
> is an "inline" desolder, and I am uncertain if this could be
> modified. Likewise, there is no specified power output for it, so I
> am unsure as to its suitability.
> 
> Another technique is to tack down the corners, apply plenty of 
liquid flux
> and 'flood' the leads by dragging a blob of solder along them. 
Clean off the
> excess solder with desolder braid and remake any suspect joints.
> 
> The other option I thought of is perhaps using a portable gas
> soldering iron. Rapid again sell a 70W equivalent gas soldering iron
> with a hot air tip, and I wondered if anyone has tried one of these
> to see if it works?
> 
> My other concern is that I will be manufacturing the board using the
> Resources at my University, which are just like any other "school"
> PCB manufacturing tools using etching chemicals - am I likely to get
> the "resolution" needed for etching the pads onto the PCB for this
> component using the chemical etching process or will this also be
> problematic?
> 
> If the lead spacing is 0.5 mm this could be tricky. 0.65 mm should 
be OK.
> 
> 
> 
> Leon Heller, G1HSM
> Email: aqzf13@d...
> My low-cost Philips LPC210x ARM development system:
> http://www.geocities.com/leon_heller/lpc2104.html



You did miss one option.  paste flux and the oven.

The smother, then uncover is the way a lot of people do it.

Another option is to google a little more.   I read a how-to on 
taking a standard high watt iron, adding some small copper pipe and a 
small fish pump to make your hot blow gun.

IIRC, he used steel wool to hold the copper away from the iron and 
that acted to help pick up the heat.

some small tip, probably a little beating action and you get a narrow 
tip.  Use a Tee connector on the copper to let you connect your 
tubing.  I think I would extend the tubing back along the handle and 
wrap it with some sort of insulation so as to make the plastic 
contatc a cooler place than near the tip

good luck!

Dave

Dave Mucha wrote:

> Another option is to google a little more.   I read a how-to on 
> taking a standard high watt iron, adding some small copper pipe and a 
> small fish pump to make your hot blow gun.
> 
> IIRC, he used steel wool to hold the copper away from the iron and 
> that acted to help pick up the heat.
> 


   I think the main goal for the wool was to transfer heat and to block most of 
the airflow so it wouldn't cool the iron too much or blow parts from the board, 
most aquarium air pumps have a pretty good output.  Have to agree that design 
looked very servicable and cheap, haven't built it myself since I use other 
means, but have an old desolderer and air pump on hand and keep the idea in mind 
if there is ever a need.  With good solder paste and technique it might do well 
for SM without the retouch step of solder and remove method, and not require 
firing up an oven for just the now and then SM part.

Alan

Fot what you want to do, forget the heat transfer method although if 
you read www.pulsar.gs guy he claims miracles like a southern 
preacher. Give it a shot and let us know. Mike



--- In Homebrew_PCBs@yahoogroups.com, Alan King <alan@n...> wrote:
> Dave Mucha wrote:
> 
> > Another option is to google a little more.   I read a how-to on 
> > taking a standard high watt iron, adding some small copper pipe 
and a 
> > small fish pump to make your hot blow gun.
> > 
> > IIRC, he used steel wool to hold the copper away from the iron 
and 
> > that acted to help pick up the heat.
> > 
> 
> 
>    I think the main goal for the wool was to transfer heat and to 
block most of 
> the airflow so it wouldn't cool the iron too much or blow parts 
from the board, 
> most aquarium air pumps have a pretty good output.  Have to agree 
that design 
> looked very servicable and cheap, haven't built it myself since I 
use other 
> means, but have an old desolderer and air pump on hand and keep the 
idea in mind 
> if there is ever a need.  With good solder paste and technique it 
might do well 
> for SM without the retouch step of solder and remove method, and 
not require 

> firing up an oven for just the now and then SM part.
> 
> Alan

mikezcnc wrote:
> Fot what you want to do, forget the heat transfer method although if 
> you read www.pulsar.gs guy he claims miracles like a southern 
> preacher. Give it a shot and let us know. Mike
> 
>>   I think the main goal for the wool was to transfer heat and to 
> 
> block most of 
> 
>>the airflow so it wouldn't cool the iron too much or blow parts 
> 
> from the board, 
> 

   That is transfer heat from the iron to the air flowing by.  Not sure where 
you were seeing anything about heat transfer method as in toner, this is talking 
about SM hot air soldering.

Alan

Alan,

you missed his original question(S): one was about method and went 
into resolution and the second question was about air pencil. 
Hopefully it helps.

Mike


--- In Homebrew_PCBs@yahoogroups.com, Alan King <alan@n...> wrote:
> mikezcnc wrote:
> > Fot what you want to do, forget the heat transfer method although 
if 
> > you read www.pulsar.gs guy he claims miracles like a southern 
> > preacher. Give it a shot and let us know. Mike
> > 
> >>   I think the main goal for the wool was to transfer heat and to 
> > 
> > block most of 
> > 
> >>the airflow so it wouldn't cool the iron too much or blow parts 
> > 
> > from the board, 
> > 
> 
>    That is transfer heat from the iron to the air flowing by.  Not 
sure where 
> you were seeing anything about heat transfer method as in toner, 
this is talking 

> about SM hot air soldering.
> 
> Alan