Wave soldering
Wave soldering is a bulk soldering process used in the
manufacture of printed circuit boards. The circuit board
is passed over a pan of molten solder in which a pump
produces an upwelling of solder that looks like a
standing wave. As the circuit board makes contact with
this wave, the components become soldered to the board.
Wave soldering is used for both through-hole printed
circuit assemblies, and surface mount. In the latter case,
the components are glued onto the surface of a printed
circuit board (PCB) by placement equipment, before
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being run through the molten solder wave. Wave
soldering is mainly used in soldering of through hole
components.
As through-hole components have been largely replaced by surface
mount components, wave soldering has been supplanted by reflow
soldering methods in many large-scale electronics applications.
However, there is still significant wave soldering where surface-
mount technology (SMT) is not suitable (e.g., large power devices
and high pin count connectors), or where simple through-hole
technology prevails (certain major appliances).
Selective soldering machine
Contents
Wave solder process
Fluxing
Preheating
Cleaning
Finish and quality
Solder types
Temperature and time graph showing
Effects of cooling rate wave soldering solder pot and
topside temperatures
Thermal profiling
Solder Wave Height
See also
References
Further reading
Wave solder process
There are many types of wave solder machines; however, the
basic components and principles of these machines are the
same. The basic equipment used during the process is a
conveyor that moves the PCB through the different zones, a pan
of solder used in the soldering process, a pump that produces
the actual wave, the sprayer for the flux and the preheating pad.
The solder is usually a mixture of metals. A typical leaded
solder has the chemical makeup of 50% tin, 49.5% lead, and
0.5% antimony.[1] The Restriction of Hazardous Substances
Directive (RoHS) has led to the elimination of leaded solder in
modern manufacturing however, and lead-free alternatives are
A simple wave soldering machine.
used. Both tin-silver-copper and tin-copper-nickel alloys are
commonly used, with one common alloy (SN100C) being
99.25% tin, 0.7% copper, 0.05% nickel and <0.01%
germanium.[2]
Fluxing
Flux in the wave soldering process has a primary and a secondary
objective. The primary objective is to clean the components that are
to be soldered, principally any oxide layers that may have formed.[3]
There are two types of flux, corrosive and noncorrosive. Wave solder optimizer fixture
Noncorrosive flux requires precleaning and is used when low acidity example showing sensors
is required. Corrosive flux is quick and requires little precleaning,
but has a higher acidity.[4]
Preheating
Preheating helps to accelerate the soldering process and to prevent thermal shock.[5]
Cleaning
Some types of flux, called "no-clean" fluxes, do not require cleaning; their residues are benign after the
soldering process.[6] Typically no-clean fluxes are especially sensitive to process conditions, which may
make them undesirable in some applications.[6] Other kinds of flux, however, require a cleaning stage, in
which the PCB is washed with solvents and/or deionized water to remove flux residue.
Finish and quality
Quality depends on proper temperatures when heating and on properly treated surfaces.
Defect Possible causes Effects
Cracks Mechanical Stress Loss of Conductivity
Contaminated surface
Reduction in strength
Cavities Lack of flux
Poor conductivity
Insufficient preheating
Susceptible to stress
Wrong solder temperature
Wrong solder thickness Too thin for current load
Wrong conveyor speed
Undesired bridging between paths
Poor Conductor Contaminated solder Product Failures
Solder types
Different combinations of tin, lead and other metals are used to create solder. The combinations used depend
on the desired properties. The most popular combinations are SAC (Tin(Sn)/Silver(Ag)/Copper(Cu)) alloys
and Sn63Pb37 (Sn63A) which is 63% tin, 37% lead. The latter combination is strong, has a low melting
range, and melts and sets quickly. Higher tin compositions give the solder higher corrosion resistances, but
raise the melting point. Another common composition is 11% tin, 37% lead, 42% bismuth, and 10%
cadmium. This combination has a low melting point and is useful for soldering components that are
sensitive to heat. Environmental and performance requirements also factor into alloy selection. Common
restrictions include restrictions on lead (Pb) when RoHS compliance is required and restrictions on pure tin
(Sn) when long term reliability is a concern.[7][8]
Effects of cooling rate
It is important that the PCBs be allowed to cool at a reasonable rate. If they are cooled too fast, then the PCB
can become warped and the solder can be compromised. On the other hand, if the PCB is allowed to cool
too slowly, then the PCB can become brittle and some components may be damaged by heat. The PCB
should be cooled by either a fine water spray or air cooled to decrease the amount of damage to the board.[9]
Thermal profiling
Thermal profiling is the act of measuring several points on a circuit board to determine the thermal
excursion it takes through the soldering process. In the electronics manufacturing industry, SPC (Statistical
Process Control) helps determine if the process is in control, measured against the reflow parameters defined
by the soldering technologies and component requirements.[10] Products like the Solderstar WaveShuttle and
the Optiminer have been developed special fixtures which are passed through the process and can measure
the temperature profile, along with contact times, wave parallelism and wave heights. These fixture
combined with analysis software allows the production engineer to establish and then control the wave
solder process.[11]
Solder Wave Height
The height of the solder wave is a key parameter that needs to be
evaluated when setting up the wave solder process.[12] The contact
time between the solder wave and assembly being soldered is
typically set to between 2 and 4 seconds. This contact time is
controlled by two parameters on the machine, conveyor speed and
wave height, changes to either of these parameters will result in a
change in contact time. The wave height is typically controlled by
increasing or decreasing the pump speed on the machine. Changes
can be evaluated and checked using a tempered glass plate, if more
detailed recording are required fixture are available which digitally
record the contact times, height and speed.
An example fixture used for capturing
See also process data from the wave
soldering machine
Dip soldering
Thermal profiling
Solder mask
References
1. Robert H. Todd, Dell K. Allen, Leo Alting (1994).
Manufacturing Processes Reference Guide (https://books. Contact times and shape of wave
google.com/books?id=6x1smAf_PAcC&pg=PA393). solder on underside of PCB
p. 393.
2. "SN100C Solder" (http://www.aimsolder.com/sites/default/fi
les/sn100c-sell-sheet.pdf) (PDF). aimsolder.com.
3. [1] (https://web.archive.org/web/20140314014419/http://w
ww.ipctraining.org/dvd/47c/script.pdf)
4. Todd p. 396
5. Michael Pecht (1993). Soldering Processes and
Equipment (https://books.google.com/books?id=Mu0o3X_
k7p8C&pg=PA56). p. 56.
6. Giles Humpston, David M. Jacobson (2004). Principles of
Soldering (https://books.google.com/books?id=cQ6khQSc
BF4C&pg=PA118&). p. 118.
7. Todd p. 395
8. "THE QUICK POCKET REFERENCE FOR TIN/LEAD
AND LEAD-FREE SOLDER ASSEMBLY" (http://www.aims
older.com/sites/default/files/soldering_handbook_rev_10-1
3.pdf) (PDF). aimsolder.com.
9. Todd, Robert H.; Allen, Dell K.(1994). Manufacturing
Processes Reference Guide. New York: Industrial Press
Inc.
10. "IPC-7530 Guidelines for Temperature Profiling for Mass
Soldering Processes (Reflow & Wave)" (http://www.ipc.org/
TOC/IPC-7530.pdf) (PDF). ipc.org.
11. "Wave Solder Optimizer" (https://www.solderstar.com/en/s
olderstar-solutions/solutions-waveselective/waveshuttle-pr
o/). www.solderstar.com.
12. "Importance of Wave Height Measurement in Wave Solder
Process Control" (https://www.solderstar.com/files/2315/51
46/5715/Importance_of_wave_solder_height_in_wave_sol
dering.pdf) (PDF). solderstar.com.
Further reading
Seeling, Karl (1995). A study of lead-free alloys. AIM, 1, Retrieved April 18, 2008, from [2] (http
s://web.archive.org/web/20030403195722/http://www.aimsolder.com/techarticles/A%20Study%
20of%20Lead-Free%20Solder%20Alloys.pdf)
Biocca, Peter (2005, April 5). Lead-free wave soldering. Retrieved April 18, 2008, from
EMSnow Web site: [3] (https://web.archive.org/web/20060219232231/http://www.emsnow.com/
npps/story.cfm?ID=10669)
Electronic Production Design & Test (2015, February 13) The importance of wave height
measurement in wave solder process control (http://www.epdtonthenet.net/article/90533/The-i
mportance-of-wave-height-measurement-in-wave-solder-process-control.aspx)
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