That certainly matches my experience, which I had
put down to being supplie dfrom a reject batch.

So, what can we do as Radio Hams to prevent such
a problem?

How hot does the whole board have to be raised before
applying a solfering iron? Would a hairdryer do?

"Terry Given" wrote in message
...
Larry Brasfield wrote:
Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly
at one end can fracture the ceramic. This can lead to excess noise
or a tendency to break down at a lower than rated voltage as
moisure gets into the crack(s). The insidious aspect of this kind
of damage is that it can show up in the field, quite some time
after the parts perform alright in initial testing.

This is a VERY good point. Reflow ovens have very well controlled
thermal profiles, slowly ramping temperature to a plateau, holding,
slowly ramping up to final tmep, holding etc. Mostly to avoid this
thermal shock related mechanical failure mechanism. High voltage
ceramics are especially prone to this - hand soldering them is a risky
process.

I once used 2 x 15nF 1000V smt X7R caps in series across an 80-800Vdc
supply for a smps application. During testing one smps failed
catastrophically (two others ran fine). Detailed examination of the
corpse showed a blast pattern radiating outward from one of the caps,
which had ruptured. The resulting mess sprayed directly across the legs
of one of the FETs, thereby toasting the unit. At the time it was
operating at a DC bus voltage of around 400V, so the cap was nowhere
near its rated voltage, more like 20%. One of the guys I worked with had
extensive experience in this area (hi-rel smps hybrids for
il/aerospace), and showed us what went wrong. We immediately replaced
the capacitors, carefully using a manual hot air station, to both
preheat and solder. The units operated continuously into a dead short at
800Vdc, no problems - there were other issues of course, it was a
pre-production protoype, but none of the explosive kind.

Airy R. Bean wrote:
That certainly matches my experience, which I had
put down to being supplie dfrom a reject batch.

So, what can we do as Radio Hams to prevent such
a problem?

How hot does the whole board have to be raised before
applying a solfering iron? Would a hairdryer do?

"Terry Given" wrote in message
...

Larry Brasfield wrote:

Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly

--snip--



Folks are starting to experiment with reflow soldering in toaster ovens.
I've read good reports on the web, but have absolutely no personal
experience nor have I even talked to someone who's done it, so I can't
vouch for it. One of these days I'll give it a try, in the meantime you
can search on toaster oven reflow and get a slew of pages.

There's at least one company (www.pcbexpress.com) who'll even make
prototype stencils for your solder paste, although for stuff that's not
too fine you can dispense paste from a syringe.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Larry Brasfield wrote:

Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly

Get a decent temperature controlled soldering iron, run it at 600F/315C
and use low melting point solder. No need for preheating or any other
messing about.

On some boards chips can be tricky to remove because they are glued in
place.

Steve

Have you seen my new soldering iron?
http://www.seattlerobotics.org/encod...6/oven_art.htm

w9gb


"Tim Wescott" wrote in message
...
Airy R. Bean wrote:
That certainly matches my experience, which I had
put down to being supplie dfrom a reject batch.

So, what can we do as Radio Hams to prevent such
a problem?

How hot does the whole board have to be raised before
applying a solfering iron? Would a hairdryer do?

"Terry Given" wrote in message
...

Larry Brasfield wrote:

Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly

--snip--



Folks are starting to experiment with reflow soldering in toaster ovens.
I've read good reports on the web, but have absolutely no personal
experience nor have I even talked to someone who's done it, so I can't
vouch for it. One of these days I'll give it a try, in the meantime you
can search on toaster oven reflow and get a slew of pages.

There's at least one company (www.pcbexpress.com) who'll even make
prototype stencils for your solder paste, although for stuff that's not
too fine you can dispense paste from a syringe.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

OK, so this is basically emulating the reflow process. The only issue with
this is that there is no real temperature control and you can damage both
the board and the components if you are not careful (as is the case with all
soldering).

The technique I use is lots of flux and a soldering iron. It is key to use
flux so that the solder flows properly. Sometimes a microscope is required
and then occasional washing to remove the solidified gunky flux [wash in
ethyl alcohol]. However if you want to solder an IC you can run the
soldering iron along the side of the IC. Slope the board and then run the
soldering iron down the board from the top most pin to the bottom most one
and the solder meniscus will stick/flow with the soldering iron. You will
end up with the last 2 or 3 pins with a bridge which can easily be removed
with solder braid. You do however need to tack the IC down to start off
with so that it doesn't move whilst soldering. I learned this from a very
skilled tech and it works incredibly well. Especially for 25-50mil pitch
QFPs. For Passives, it's a lot of work and the technique given in the link
below may be better if you have lots of them.

**FLUX** is always key though! Water soluble if possible as it's easier to
clean off. Just wash it and wait for it to dry. Don't try and heat it dry
since this can cause steam to form under the solder joints (and the ICs) and
cause adverse pressure. The pressure can cause joints to fail and parts to
crack.

I would also like to point out something else about the technique given in
the link below. Bake out! One real issue in SMT soldering is that IC's
have to be baked out if they've been sitting in a normal environmnet
(humidity) since the epoxy absorbs water. The water then gets heated by the
IR reflow process/oven and can cause the IC to crack. The way around this
is to heat the IC/components gently to above 100 deg C (125 deg C is OK).
This bkes out the water. USually in an industrial process this is done for
about an hour or 2. The IC's are then sealed in a waffle tray and bag with
anhydrous silicone crystals to make sure no water gets reabsorbed. You
shoudl only be wary of this if your IC's have been lying around in a damp
warm atmosphere for a few days. For normal prototyping this is not so much
of a problem.



You can also get the reflow "hairdryer" kinds of devices. These work well
also and are a little bit more controllable than an oven. If you paste as
described by the link below, just heat around the IC/components until the
solder goes shiny. It'll reflow at that point. Let it cool off and check
it.



"w9gb" wrote in message
news:Q_vrd.178384$HA.36082@attbi_s01...
Have you seen my new soldering iron?
http://www.seattlerobotics.org/encod...6/oven_art.htm

w9gb


"Tim Wescott" wrote in message
...
Airy R. Bean wrote:
That certainly matches my experience, which I had
put down to being supplie dfrom a reject batch.

So, what can we do as Radio Hams to prevent such
a problem?

How hot does the whole board have to be raised before
applying a solfering iron? Would a hairdryer do?

"Terry Given" wrote in message
...

Larry Brasfield wrote:

Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly

--snip--



Folks are starting to experiment with reflow soldering in toaster ovens.
I've read good reports on the web, but have absolutely no personal
experience nor have I even talked to someone who's done it, so I can't
vouch for it. One of these days I'll give it a try, in the meantime you
can search on toaster oven reflow and get a slew of pages.

There's at least one company (www.pcbexpress.com) who'll even make
prototype stencils for your solder paste, although for stuff that's not
too fine you can dispense paste from a syringe.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

It is interesting to note that if you look at one of the winners (Robert
Lacoste) of the Circuit Cellar design contest (Steve Ciarcia's embedded
microcontroller design magazine) ... he addressed many of the issues that
you raised.
http://www.circuitcellar.com/library..._168/index.htm

In fact enough, with a $150 toaster oven and a low-cost controller, he
achieved reflows with good results. A few mfg. were very interested in his
design and approach (Robert has his own consulting company in France).

gb

"crzndog" wrote in message
...
OK, so this is basically emulating the reflow process. The only issue
with this is that there is no real temperature control and you can damage
both the board and the components if you are not careful (as is the case
with all soldering).

I would also like to point out something else about the technique given in
the link below. Bake out! One real issue in SMT soldering is that IC's
have to be baked out if they've been sitting in a normal environmnet
(humidity) since the epoxy absorbs water. The water then gets heated by
the IR reflow process/oven and can cause the IC to crack. The way around
this is to heat the IC/components gently to above 100 deg C (125 deg C is
OK). This bkes out the water. USually in an industrial process this is
done for about an hour or 2. The IC's are then sealed in a waffle tray
and bag with anhydrous silicone crystals to make sure no water gets
reabsorbed. You shoudl only be wary of this if your IC's have been lying
around in a damp warm atmosphere for a few days. For normal prototyping
this is not so much of a problem.

"w9gb" wrote in message
news:Q_vrd.178384$HA.36082@attbi_s01...
Have you seen my new soldering iron?
http://www.seattlerobotics.org/encod...6/oven_art.htm

w9gb


"Tim Wescott" wrote in message
...
Airy R. Bean wrote:
That certainly matches my experience, which I had
put down to being supplie dfrom a reject batch.

So, what can we do as Radio Hams to prevent such
a problem?

How hot does the whole board have to be raised before
applying a solfering iron? Would a hairdryer do?

"Terry Given" wrote in message
...

Larry Brasfield wrote:

Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly

--snip--



Folks are starting to experiment with reflow soldering in toaster ovens.
I've read good reports on the web, but have absolutely no personal
experience nor have I even talked to someone who's done it, so I can't
vouch for it. One of these days I'll give it a try, in the meantime you
can search on toaster oven reflow and get a slew of pages.

There's at least one company (www.pcbexpress.com) who'll even make
prototype stencils for your solder paste, although for stuff that's not
too fine you can dispense paste from a syringe.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com