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So you think you can
SOLDER?
by Nicholas Vinen
It’s a critical skill for electronics professionals and hobbyists but many of
us have minimal or no formal training in soldering. To find out what we
could learn, I attended an IPC soldering training and certification course
which is suitable for beginners through to experienced professionals. I
learned more than I expected about soldering, rework and PCB repair
and there were some surprises too.
I
f you’re going to build or repair
any electronic gear and expect it to
last (especially in abusive environments such as marine or automotive),
you will need good soldering skills.
Bad solder joints are a major cause of
failures in both commercial equipment
and kits. We’ve met kit constructors
who have gone to the trouble of building a PCB, spent time trouble-shooting
it and eventually gave up when the
problem was simply a few incomplete
or unreliable joints.
To make matters worse, these days
many new ICs come only in surfacemount packages; in some cases your
only choice is a fine-pitch or even
leadless IC.
This means that some projects inevitably require more advanced soldering
skills. Many potential constructors
feel daunted taking these on but with
a little practice and the right tools, it
isn’t too difficult.
This learning curve is so much less
steep if you have guidance from an
experienced technician to learn the
tricks which make it easy to solder
these more difficult devices. These
are exactly the sort of skills you will
We spent much of our time at the well-stocked workbenches, practising
our technique using the supplied PCBs, parts and consumables. However
we also watched some videos, slide shows, live demonstrations and had
numerous discussions about soldering theory and techniques. IPC Certified
Trainer Andrew Brown guided us through the course, checked our work
and gave constructive feedback based on the results.
22 Silicon Chip
siliconchip.com.au
Day three and with our PCBs complete and working, we practiced
terminating wire onto various kinds of PCB terminals. These wires were
then soldered to the board as a way to keep them all together. More
experienced attendees who finished tasks early were able to try different
techniques or ask questions. One unusual tool seen here is a timberhandled hog-bristle brush, used for cleaning PCBs and parts due to the
fact that it doesn’t generate static electricity.
pick up attending a soldering training
course such as the one described here.
I was invited to attend a 3-day
course called “IPC-7711/7721 Rework/
Repair Modification”. IPC is an international organisation and their name
originally stood for the “Institute for
Printed Circuits”. They now go by
the name “Association Connecting
Electronics Industries” but still use the
widely-recognised initials IPC.
The IPC produces global standards
for PCB design, manufacturing and
electronics assembly, including soldering.
This training was provided by an
IPC Certified Trainer from Chemtools
Pty Ltd, at their office in St Marys,
western Sydney.
This particular course included
removing and replacing through-hole,
surface-mount components on a PCB,
pad and track repair, PCB laminate
repair, wire splicing and conformal
coating. However, the exact mix of
subjects varies a little, depending on
the requirements of the attendees.
I learned a lot at this course but it
was also very enjoyable. The group
was small, with a total of nine attendees which is typical. This gives a lot
of opportunity to ask questions. It also
means personal attention and feedback
from the trainer.
siliconchip.com.au
The other eight attendees ranged
from a complete beginner through to
experienced service and manufacturing personnel (yes, there are still electronics manufacturers in Australia!).
By the end of the course, the beginner had successfully soldered a wide
variety of through-hole and surfacemount devices and went away a lot
more capable and confident than just
three days earlier.
Some surprises
He obviously got a lot out of the
course but so did many of the more
experienced members of the group,
myself included. One of the aspects I
especially liked was the opportunity
to try various different techniques for
doing the same job.
For example, one part of the course
involved soldering a very fine pitched
(0.4mm lead spacing) Thin Quad
Flat Pack (TQFP) IC. The instructor
explained three different methods to
solder this part, demonstrated one and
stated that we could use whichever
we wanted.
I elected to use a method which I had
not tried before, which involved placing a thin layer of solder on the pads,
locating the IC accurately over them,
applying flux and then re-heating the
pads (and component leads) with a
standard iron so the solder ‘reflows’
onto the device leads. This is a similar
approach to one of the most common
commercial soldering methods (infrared reflow) but without needing any
special gear.
It was gratifying that this not only
worked but as the instructor promised,
made a series of near-perfect joints
with a minimal amount of solder. He
also gave us the option of using solder
paste and a hot air gun (ie, the aforementioned reflow technique) or using
a “mini-wave” type soldering iron tip.
So even though I have successfully
soldered many similar ICs in the past, I
came away from the course with some
new tricks.
I also got the opportunity to use a
“Mantis” 3D microscope for the first
time, which is a great piece of gear for
fine work and inspection if you can
afford it. We were allowed to use it
as necessary for placing components,
checking placement and inspecting
joints.
Lead-free soldering
The IPC-7711/7721 training course
is not specific to any particular type of
solder alloy or brand/model of tools. It
is a general soldering training course
and the knowledge gained by the participants can be used with virtually
April 2014 23
A demonstration of
reflowing BGA package
chips on an XBox
motherboard using an
infrared heater rework
system. This has a preheater under the PCB
and the main heater
on top, which is aimed
at the area to reflow. A
thermistor on the end
of a stiff wire allows
the user to monitor the
temperature. The preheat is important since
without it there would
be a high likelihood of
PCB damage (the board
sagged visibly during
reflow). This was not
part of the course as
such but we were all
interested in seeing
how it’s done so the
trainer obliged.
any equipment. But having said that,
the Chemtools IPC training courses
use lead-free products when possible
and it was an eye-opening experience
to say the least.
While I have reworked and repaired
some commercially-made boards that
used lead-free solder, it wasn’t much
fun because these boards typically
use SAC305 lead-free solder (96.5%
tin, 3% silver and 0.5% copper). It
melts at a relatively high temperature
(~220°C), is non-eutectic and forms
dull, crystalline-looking solder joints
no matter what you do.
That makes solder joint inspection much more difficult and hence
requires good technique to give consistent results.
Before going any further, we should
explain what “eutectic” means. Solder
comprising 63% tin and 37% lead
(63/37) is eutectic, which means that it
transitions between its solid and liquid
states at a single temperature, 183°C.
By comparison, 60/40 solder is
fully liquid (liquidus) above about
190°C and solid (solidus) below 183°C.
Between these temperatures it is in
a semi-solid or “plastic” state and if
the joint is disturbed while between
24 Silicon Chip
these temperatures during cooling, it
will form a poor joint with cracks and
other problems. Eutectic alloys do not
have this in-between state and so are
easier to work with.
By comparison, SAC305 lead-free
solder isn’t too bad, with a plastic
range of just 217-220°C but this is still
not ideal. Note that this is substantially
higher than the 183°C melting point
of 63/37.
But it’s the dull, crystalline appearance of the solidified joints that is its
worst aspect and it’s quite expensive
too, due to the relatively high silver
content.
At the IPC training course we exclusively used a lead-free solder alloy
called SN100C, which was developed
by Nihon Superior Co of Japan but is
also manufactured by AIM Solder.
This comprises 99.3% tin, 0.7% copper plus trace amounts of nickel and
germanium. It is eutectic with a melting point of 227°C.
Besides the higher melting point,
working with SN100C is not dissimilar
to working with traditional tin-lead
solders. It pays to ensure that the PCB
is clean (ie, no oxide contamination)
and to use a little extra flux and heat
the joints for slightly longer, but it
flows smoothly and otherwise behaves
the way we are used to with tin/lead
solders. So with good technique, it
gives excellent results every time,
with the shiny-looking fillets we want
to see.
In fact, in some tests (such as mechanical strength at low temperatures),
SN100C is superior to tin/lead solder.
And while we have not used this solder in a commercial environment, with
reflow or wave soldering, we suspect
it will be better there too, in terms of
both reliability and ease of inspection.
One of the bugbears of lead-free
solder is “tin whiskers”. Without going into a lot of detail, tin whiskers
are hair-like outgrowths which occur
spontaneously and can cause short
circuits while “tin pest” is where tin
changes its atomic structure at low
temperatures and disintegrates.
Testing has shown that tin whiskers
do occur with SN100C but to a much
lesser extent than with SAC305 (and
generally do not become long enough
to cause problems). Tin pest does not
occur with either alloy.
To summarise, lead-free soldering is
not difficult with the right solder alloy
siliconchip.com.au
and correct technique. There’s really
no disadvantage other than the slightly
higher cost of the solder itself (tin is
more expensive than lead).
If you want to try it for yourself,
Chemtools offer specific lead-free
training courses, including shorter
courses (one day or half day); more
details on this later.
For more information on SN100C,
visit www.aimsolder.com/products/
sn100c/sn100c
Chemtools products
As stated in the text, the IPC-7711/7721 course I took is not specific to any
particular equipment, tools or products and is a general soldering skills course.
However, as you may have guessed from its name, Chemtools’ primary business
is manufacturing and selling chemical products, including solder, flux, cleaning
solution, lubricants and so on. Many of the products supplied for the soldering
course are their own formulations.
That includes a syringe “AIM Australia” brand (manufactured by Chemtools) flux
paste and a spray can of Kleanium Deflux-It G2 Flux Remover. I was impressed
Thermaltronics
As explained earlier, the training
course was not about learning to use
any particular equipment.
However another notable experience was using the provided soldering irons which were Thermaltronics
TMT-9000S stations, similar to the
TMT-2000S reviewed elsewhere in
this issue.
For full details, see that review but
I will say here that I had previously
considered buying one of these irons
but had dithered over deciding on a
particular model.
My experience using them during
the course convinced me that I definitely want one, especially now that I
am considering switching to lead-free
solder as they are particularly suited
for that task.
Further experiences
While not actually on the curriculum, I was curious about working with
BGA (ball grid array) package ICs as I
had never done it before.
They are tricky because all the solder joints are under the IC package
itself so they must be reflow soldered.
BGAs are widely used in commercial
devices because they offer the highest
connection density, with some BGAs
having upwards of 1000 pads.
BGAs are supplied with small solder balls pre-attached to each land on
the underside. When the IC is placed
on the board, these balls sit on top of
corresponding pads and when heated,
reflow and form the solder joints.
While tricky to work with, they are not
out of reach of hobbyists; they can be
soldered in a toaster oven, for example.
Since several of us were interested
in how to reflow and remove BGAs and
we had finished all the required parts
of the training course, we were treated
to a demonstration of both, using an
infrared solder reflow device.
The part of the course where we
siliconchip.com.au
with the quality of both products. Their no-clean flux gel has a long residence
time, is tacky enough to be used to temporarily hold components in place and it
sticks around during soldering to provide good wetting, especially during drag
soldering. It doesn’t have a particularly strong odour, either; some fluxes can
produce quite acrid fumes.
I especially liked the Flux Remover. I have never been satisfied with isopropyl
alcohol or methylated spirits in the past because they tend to leave behind a
white residue and much scrubbing and repeated applications are required; even
then it’s virtually impossible to get the board completely clean. Not so with the
Kleanium G2 which completely removes flux residue (even when it has burned),
leaving a sparkling clean board.
It’s a slow-drying formulation so it stays on the board for long enough to
really attack any contaminants and leaves you with enough time to blot it (and
anything it has dissolved) off before it evaporates. A clean board doesn’t just look
nice, you need it to be clean to properly inspect solder joints; flux residue can
easily mask faults or give the appearance of a solder bridge where there is none.
It even smells nice and has a low toxicity, important for a product which you may
use on a regular basis. There are in fact a whole range of Kleanium products (see
photo) to suit various different situations, such as when faster drying is required
in production environments or for when a more aggressive solvent is required.
Like all the Chemtools products, the Kleanium range is made in Australia. Most
of these products can be purchased from element14 (G2 Flux Remover part code
236636402, AIM Australia flux paste part code 182777202).
The SN100C lead-free solder mentioned in the text can be purchased from RMS
Parts in wire or paste form. See the following link for details: http://rmsparts.
com.au/productsearch.ews?stocksearch.ewdsearchterm=sn100c
SN100C solder is manufactured by either Nihon Superior Co of Japan or AIM
Solder, including AIM Australia (a brand of Chemtools).
April 2014 25
learned how to strip and tin wire and
make connections to various kinds of
terminals was also quite interesting
as I had never used a turret, hook or
cup terminal before and I learned better methods of stripping and tinning
wire than I had been using previously.
It may seem like a simple task but
there are some serious pitfalls which
can cause premature failure of a wire
connection.
It was also interesting to get a chance
to apply a conformal coating to a PCB.
While there is nothing especially difficult about this, I had not done so
before, partly because I didn’t know
what to do to remove that coating
later should it be necessary to perform
repairs.
I got some helpful hints on what’s required for removal and on the benefits
of conformal coating, such as much
better corrosion resistance in applications where the PCB can be exposed to
moisture and condensation.
Other courses
I would definitely recommend the
IPC-7711/7721 course to anybody
who wants to learn how to solder or
improve their existing skills as it covered a wide range of topics including
many important techniques.
But you may not necessarily have
the time to take a 3-day course or feel
that the cost is justified.
Chemtools also offer a number of
other IPC training courses including
one-day courses which readers may
wish to attend. Note that many of these
(including the one I attended) consist
of a core curriculum and optional
modules which teach additional skills
and knowledge.
In general, I would recommend including as many modules as possible.
In addition to IPC-7711/7721, the
available courses include:
• Fundamentals of Soldering: 1-day
course includes soldering SMD &
through-hole components, cleaning,
inspection, equipment maintenance
and lead-free soldering. Consumables and tools provided.
• Introduction to ESD (Electrostatic
Discharge): a 2-hour course covering
ESD and ESD mitigation techniques
and tools.
• Advanced SMT & Through-Hole
Rework/Repair course: a 1-day
course with the option of a second
day for hands-on PCB repair training. Includes soldering fine-pitched
26 Silicon Chip
This is the practice
board I assembled
as part of the
training course.
As you can see,
it has a number
of different types
of components
including various
different kinds
of surface-mount
parts with varying
pitches and lead
types. We used a
variety of different
methods to solder
these components
and inspected the
joints to ensure
they were formed
correctly. We also
covered it with a
conformal coating
(which glows
under UV light,
so you can check
that it is fully
covered). This
coating has a shiny
appearance and
protects the board
and components
from dirt, dust and
moisture.
•
•
•
•
•
packages using a hand-held iron,
hot-air wand or infrared equipment,
through-hole component removal
using vacuum desoldering tools,
cleaning, equipment maintenance
and lead-free soldering.
Lead-free soldering: 1-day course,
covering specific requirements of
using lead-free solder as well as
general soldering skills.
Production Line Soldering: 1-day
or 2 x ½ day course.
Acceptability of Electronic Assemblies (IPC-A-610E): A 3-day course
covering skills required to accurately recognise faults in electronic
assembly (eg, poor solder joints).
Requirements for Soldered Electrical and Electronic Assemblies
(IPC-J-STD 001E): A course covering
the processes and procedures for
reliable soldering and inspection
of through-hole, SMD components,
wires and terminals.
Requirements and Acceptance for
Cable and Wire Harness Assemblies
(IPC/WHMA-620B): Covers crimp
termination, insulation displacement connectors, soldered terminations, moulding, potting, splicing, bundling, marking, labelling,
solderless wire wrap connections
and more.
Attendees who complete IPC courses, show satisfactory performance and
pass the test are qualified as Certified
IPC Specialists. This certification is
valid for two years (with the possibility of a 90-day extension to allow for
re-certification).
Chemtools travel around Australia,
offering courses in major cities at various times.
If you in or near a major Australian
city and are interested in attending a
course, call them at 1300 738 250 or
(02) 9623 3670. Also, check their website: www.ipctraining.com.au
Courses are scheduled when there
are enough participants to make a
class, so they may be able to offer you a
place in a course that has already been
scheduled or alternatively, you can wait
SC
until one becomes available.
siliconchip.com.au
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