Maker Pro
Maker Pro

Soldering surface mount components

  • Thread starter Daniel Kelly \(AKA Jack\)
  • Start date
C

Clarence

Jan 1, 1970
0
Larry Brasfield said:
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.

At Siemens Ultrasound, we learned this the hard way, then had it
confirmed by at least one vendor's examination of abused parts.

--Larry Brasfield

Of course this may have actually happened, and Boy, you had some pretty lousy
assembly people. I've seen the pre-prod units used for test assembled and
soldered by hand and subjected to extensive testing. Never saw a solder
related failure of a component. We tested for very long periods on many
boards. Of course we also inspected the boards before applying power and
checking for damage. Rarely had to retouch a board after the first three.
 
T

Terry Given

Jan 1, 1970
0
Larry said:
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.

At Siemens Ultrasound, we learned this the hard way, then had it
confirmed by at least one vendor's examination of abused parts.

...

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.

Cheers
Terry
 
J

John Larkin

Jan 1, 1970
0
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.

At Siemens Ultrasound, we learned this the hard way, then had it
confirmed by at least one vendor's examination of abused parts.

Maybe the parts are getting better, but I've never seen that happen,
and some of our boards have lots of parts on the bottom,
hand-soldered. I hand-solder all kinds of parts in the lab, and can't
recall ever damaging one, unless it wasn't on a PCB, like soldered
directly to a connector or on a copperclad breadboard, where it is
possible to apply some bending forces and rip off the end caps.

We have virtually zero returns from the field due to damaged passives.

John
 
H

Howard Long

Jan 1, 1970
0
"Steven McGahey" <[email protected] (remove
the obvious bits)> wrote in message
Hi all,

I've read this thread with a lot of interest, as I have a small bit of
surface-mount work to do, but no experience working with these tiny
components.

I would have thought that when working with these components, you would
have > to use a different approach, and try to keep the component cool (as
it'll
fry otherwise), but this thread seems to suggest otherwise.

FWIW, I use a standard temperature controlled iron with a small tip (I think
it cost about $50), with very thin solder, desolder braid.

I do everyting on a plain white tray with lips around the edge - there's
nothing worse than losing that last 3.3k resistor you had on the carpet...

I do have a small magnifying glass, but that's just to help me identify the
components that actually have markings - I don't use it for anything else.

For the chips with loads of pins at tiny spacing (including 0.5mm), I use a
really tiny piece of bluetak (a bit like plasticine or playdoh, but sticks
paper to walls) to fix the component into place, then I solder the
component. I don't worry too much about solder bridges over the leads for
now, but I am rather careful to use small amounts of solder, in case it
creeps under the chip.

Then I use the desolder braid to mop up the excess solder. After a visual
inspection, I do a continuity check of each of the leads to ensure there's
connection to the pcb as well as no shorts between adjacent leads of the
chip. A pain, and almost every time it shows nothing untoward.

Rework involving removal of chips takes a number of tricks, but primarily
remember that you're much more interested in maintaining the PCB in good
shape, at the expense of a trashed component.

Good luck. Howard.
 
L

Larry Brasfield

Jan 1, 1970
0
Clarence said:
Of course this may have actually happened,

Yes, of course.
and Boy, you had some pretty lousy assembly people.

They were quite skilled and competent, generally. If you knew
the circumstances under which the hand soldering occured, you
might not be so willing to denigrate them. (But who knows?)
I've seen the pre-prod units used for test assembled and
soldered by hand and subjected to extensive testing. Never saw a solder
related failure of a component.

To see the excess noise phenomenon, you would have to be
looking at a circuit handling low level signals which would be
affected by random parametric shifts. To see the drop in
voltage withstand, you would have to be using parts at an
appreciable fraction of their rated voltage, or subject them
to conditions under which moisture would enter the cracks.
So the fact that you never saw that is not much reassurance.
We tested for very long periods on many boards.

But what were you testing for? Did the environment
promote moisture ingression into the cracks? Was there
thermal cycling? I must say, your failure to see that
phenomenon is weak evidence against its reality.
Of course we also inspected the boards before applying power and
checking for damage. Rarely had to retouch a board after the first three.

The damage I mentioned is nearly impossible to see without
a microscope. Typically, the micro-cracks do not extend
clear thru the part, and they tend to be closed, being held
together by the unbroken material. I doubt your inspection
would have caught that damage.

The facts I have related regarding the failure mechansim,
and the strong disrecommendation against hand soldering
ceramic SMD capacitors, came to me directly from a well
known and reputable supplier of such parts. You, or other
"we got away with something, so it must be fine" kind of
folks can disregard it and often not pay the price. Those
who desire reliability will more likely heed it.
 
T

Terry Given

Jan 1, 1970
0
Larry said:
Yes, of course.




They were quite skilled and competent, generally. If you knew
the circumstances under which the hand soldering occured, you
might not be so willing to denigrate them. (But who knows?)

its the rate-of-change of temperature thats the real killer. Larger caps
are worse, as the resulting dimensional changes are bigger.

To see the excess noise phenomenon, you would have to be
looking at a circuit handling low level signals which would be
affected by random parametric shifts. To see the drop in
voltage withstand, you would have to be using parts at an
appreciable fraction of their rated voltage, or subject them
to conditions under which moisture would enter the cracks.
So the fact that you never saw that is not much reassurance.




But what were you testing for? Did the environment
promote moisture ingression into the cracks? Was there
thermal cycling? I must say, your failure to see that
phenomenon is weak evidence against its reality.

ROTFLMAO!



The damage I mentioned is nearly impossible to see without
a microscope. Typically, the micro-cracks do not extend
clear thru the part, and they tend to be closed, being held
together by the unbroken material. I doubt your inspection
would have caught that damage.

doesnt everyone have a binocular microscope? how quaint.
The facts I have related regarding the failure mechansim,
and the strong disrecommendation against hand soldering
ceramic SMD capacitors, came to me directly from a well
known and reputable supplier of such parts. You, or other
"we got away with something, so it must be fine" kind of
folks can disregard it and often not pay the price. Those
who desire reliability will more likely heed it.

There are also mechanical resonance related with the larger ceramic smt
parts (Marcon have poublished several papers on this effect).

Recently I have hand-soldered about 2000 0603 caps (prototypes). Perhaps
2-3 caps failed immediately; as its a prorotype I dont care about
medium-long term reliability, but no way would I give it to a customer :)

Cheers
Terry
 
C

Clarence

Jan 1, 1970
0
Terry Given said:
its the rate-of-change of temperature that's the real killer. Larger caps
are worse, as the resulting dimensional changes are bigger.
ROTFLMAO!

Not much moisture in a near vacuum!
doesn't everyone have a binocular microscope? how quaint.

I'll take the 'disrecommendation' with a box of salt!
There are also mechanical resonance related with the larger ceramic SMT
parts (Marcon have published several papers on this effect).

Recently I have hand-soldered about 2000 0603 caps (prototypes). Perhaps
2-3 caps failed immediately; as its a prototype I don't care about
medium-long term reliability, but no way would I give it to a customer :)

Cheers
Terry

I am delighted to hear you wouldn't give your work to a customer. Many
prototypes are unsuited for the customer to see anyway due to the rework and
handling in engineering test. I NEVER ship a 'prototype' to anyone. That is
what a "first Article" is for!

As for the work I cited! These were weather Satellite boards, RF, motor
control, CPU, and digital communications, plus low level analog video, with
analog to digital conversion. There will only be 18 final units built, and
testing (with temperature cycling from -40 to + 80 Degrees C four times a day
at 5 degrees C per minute) was eight times a day, total time of a complete test
was 2,000 hours. MTTF predicted is 18 years. Also they must survive 50,000
Kilorads exposure.

Yes, Inspection under a microscope, 20 and 50 diameters magnification. Before
and after tests. Yes All boards were also tested on a shake table, they must
survive launch.

The Customer is NASA, they are very particular, and will launch the first of
these in 2006.

Shooting one's mouth off when someone tries to help causes a loss of
credibility!
Since your really an amateur, live with your poor workmanship and cry about it!
 
J

Jim Adney

Jan 1, 1970
0
I would have thought that when working with these components, you would have
to use a different approach, and try to keep the component cool (as it'll
fry otherwise), but this thread seems to suggest otherwise.

I was on the Vishay web site recently and came across a writeup they
have on hand soldering surface mount electrolytics. If you do any of
this I believe it's worth looking up. They are rather cautious and
suggest that if you spend more than 3 seconds on a junction that's too
long and you should start over with a new part.

Seems extreme to me, but they're the ones who are actually in a
position to know.

-
 
T

Terry Given

Jan 1, 1970
0
Hi Clarence,
Not much moisture in a near vacuum!




I'll take the 'disrecommendation' with a box of salt!




I am delighted to hear you wouldn't give your work to a customer. Many
prototypes are unsuited for the customer to see anyway due to the rework and
handling in engineering test. I NEVER ship a 'prototype' to anyone. That is
what a "first Article" is for!

Hear Hear!

Reflow machines are best suited to soldering smt. If you have to do it
by hand, use hot air. A bloody great soldering is the worst way.
As for the work I cited! These were weather Satellite boards, RF, motor
control, CPU, and digital communications, plus low level analog video, with
analog to digital conversion. There will only be 18 final units built, and
testing (with temperature cycling from -40 to + 80 Degrees C four times a day
at 5 degrees C per minute) was eight times a day, total time of a complete test
was 2,000 hours. MTTF predicted is 18 years. Also they must survive 50,000
Kilorads exposure.
ouch.


Yes, Inspection under a microscope, 20 and 50 diameters magnification. Before
and after tests. Yes All boards were also tested on a shake table, they must
survive launch.

The Customer is NASA, they are very particular, and will launch the first of
these in 2006.

Shooting one's mouth off when someone tries to help causes a loss of
credibility!
Since your really an amateur, live with your poor workmanship and cry about it!

What makes you think I'm an amateur? I just dont want to hire a tech
(labour laws become a real pain in the ass when you have staff).

Cheers
Terry
 
R

remove two items of clothing

Jan 1, 1970
0
Roger, John, Howard and Jim,

Thanks for your response, guys - much appreciated.

I'll give this a go with the blutack (we had the same thing in Australia -
wonder what the UK equivalent is...) and desoldering braid.

I think I also need a smaller soldering iron tip - the last one was still
too big and bulky with a 1 or 2 mm point.

Cheers,
-Steve.
 
C

Clarence

Jan 1, 1970
0
Terry Given said:
Hi Clarence,



Hear Hear!

Reflow machines are best suited to soldering smt. If you have to do it
by hand, use hot air. A bloody great soldering is the worst way.

Since that is what they were designed for, and that is what I use them for when
it is appropriate.

By the way, all these boards MAY be hand soldered in the limited production.
There are components which can be reliably flow soldered, but these boards are
populated on both sides, and depending upon weight MAY not remain in place
going through the reflow process with an already soldered side down. Ordinary
FR4 will usually work this way, but the aluminum cored boards get too hot on
the bottom when the core conducts the heat through the board. (There is no
"convection cooling" in space. Only radiation and conduction.)
it!

What makes you think I'm an amateur? I just don't want to hire a tech
(labor laws become a real pain in the ass when you have staff).
Cheers
Terry

Your statements were a strong clue, then the lack of experience added fuel. I
would hope I was wrong! I only maintain five consultants (1099) on call, all
specialists! I do the initial design, and work along side of experienced
specialists for a quality result.

Sometimes I take my entire team into a customers facility, it helps to have
people with all those training certifications and credentials.

Thanks for the warning about Macon. I'll avoid them!
 
P

Paul Burke

Jan 1, 1970
0
remove said:
I'll give this a go with the blutack (we had the same thing in Australia -
wonder what the UK equivalent is...)

Parkin
 
H

Howard Long

Jan 1, 1970
0
I'll give this a go with the blutack (we had the same thing in Australia -
wonder what the UK equivalent is...) and desoldering braid.

It's the tiniest piece of blutak - too much and the chip's leads don't rest
in contact with the PCB solder pads. This allows you to position the chip
accurately by sight over the solder pads. The blutak then remains there ad
infinitum (or until you have to rework the chip!).

In the US blutak's like this
http://www.staples.com/Catalog/Brow...Id=10000&bcClassName=Glue+&+Adhesive+Products
I think I also need a smaller soldering iron tip - the last one was still
too big and bulky with a 1 or 2 mm point.

Here's the iron I use
http://www.maplin.co.uk/Module.aspx?ModuleNo=10271&TabID=1&source=15&WorldID=9&doy=2m12

I use the same sized tip that was supplied with the iron - it's pointy but
not miniscule.

Cheers, Howard
 
T

Terry Given

Jan 1, 1970
0
Clarence said:
Since that is what they were designed for, and that is what I use them for when
it is appropriate.




By the way, all these boards MAY be hand soldered in the limited production.
There are components which can be reliably flow soldered, but these boards are
populated on both sides, and depending upon weight MAY not remain in place
going through the reflow process with an already soldered side down. Ordinary
FR4 will usually work this way, but the aluminum cored boards get too hot on
the bottom when the core conducts the heat through the board. (There is no
"convection cooling" in space. Only radiation and conduction.)




Your statements were a strong clue, then the lack of experience added fuel. I
would hope I was wrong! I only maintain five consultants (1099) on call, all
specialists! I do the initial design, and work along side of experienced
specialists for a quality result.

Sometimes I take my entire team into a customers facility, it helps to have
people with all those training certifications and credentials.

Thanks for the warning about Macon. I'll avoid them!

Actually its not Marcon per se, its just that the larger ceramic caps
have mechanical resonances that can be excited electrically. square-loop
ferrite has the same problem - witness the warnings in the Ferroxcube
databook.

Cheers
Terry
 
C

Clarence

Jan 1, 1970
0
"Terry Given" wrote
Actually its not Marcon per se, its just that the larger ceramic caps
have mechanical resonance's that can be excited electrically. square-loop
ferrite has the same problem - witness the warnings in the Ferroxcube
databook.

Cheers
Terry

Like the 2.2mF to 100mF units I normally use?

Never seen any warnings. They are not piezoelectric.
 
J

John Fields

Jan 1, 1970
0
Like the 2.2mF to 100mF units I normally use?

---
Pretty large value for ceramics, eh?
---
Never seen any warnings. They are not piezoelectric.

---
It's not necessary for a capacitor to be piezoelectric to exhibit a
mechanical resonance or to be microphonic. All that's required is for
the dielectric to be mechanically deformable by the forces exerted by
the electric field across it or for the dielectric to be deformed by
external mechanical forces.
 
T

Terry Given

Jan 1, 1970
0
Clarence said:
"Terry Given" wrote



Like the 2.2mF to 100mF units I normally use?

Never seen any warnings. They are not piezoelectric.

you use 0.1 farad ceramic caps? those I'd like to see. Whats the
dielectric? (or perhaps you use "mF" to mean micro-Farads - quaint but
confusing, given the preponderance of SI units nowadays). I did once see
a 100uF 200V (IIRC) NPO cap (mil smps). very very expensive - US$300 IIRC.

AFAICR the piezoelectric behaviour was not the issue - just electrically
exciting them at their mechanical resonant frequencies.


Cheers
Terry
 
T

Terry Given

Jan 1, 1970
0
John said:
---
Pretty large value for ceramics, eh?
---




---
It's not necessary for a capacitor to be piezoelectric to exhibit a
mechanical resonance or to be microphonic. All that's required is for
the dielectric to be mechanically deformable by the forces exerted by
the electric field across it or for the dielectric to be deformed by
external mechanical forces.

And if the mechanical resonant frequency is the same as the electrical
excitation, significant (wrt the cap) forces can build up over time.
2220 and bigger were noted in the Marcon paper.

Cheers
Terry
 
C

Clarence

Jan 1, 1970
0
C4532X7R2A225M By TDK 2.2uF 100V (since your into SI (stupid interference))
Up to and including C4532Y5V1A107Z 100uF 10V
And NOJC107M004RWJ 100uF 4V Y5V

These are all 1812 SMT parts.
you use 0.1 farad ceramic caps? those I'd like to see. What's the
dielectric? (or perhaps you use "mF" to mean micro-Farads - quaint but
confusing, given the preponderance of SI units nowadays). I did once see
a 100uF 200V (IIRC) NPO cap (mil smps). very very expensive - US$300 IIRC.

AFAICR the piezoelectric behavior was not the issue - just electrically
exciting them at their mechanical resonant frequencies.

Electrical excitation to mechanical resonance is the DEFINITION of
"piezoelectric."
 
Top