Using dissociated water, microflame terminal soldering offers an inexpensive alternative to crimped connections.
By Gary W. Miller
Microflame soldering has been used for more than 30 years in several industries. In microflame torches, hydrogen/oxygen generators literally make fire from water. Distilled or deionized water is a perfect mix of two parts hydrogen to one part oxygen, so with the right technology, water becomes fuel. Using a multicell generator, distilled or deionized water is added to an electrolytic liquid, and electrical energy is introduced. The water is then dissociated into hydrogen/oxygen gas. It can be modified as needed for the particular application and then put through small stainless steel hypodermic like tubes and used as an accurate, clean, fast, noncontact heat source.
 FIGURE 1. A small hydrogen/oxygen flame is used for high-speed noncontact soldering. |
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The patented development of multicell technology enables extremely accurate amounts of gas to be produced, which can easily be used in automation. For automated systems, especially the more sophisticated higher-speed systems, this greater accuracy and reliability is an absolute requirement. The flame produced by a hydrogen/oxygen generator is superior in several ways to gas combinations used in other applications. Because the flame is very intense in the axial direction only, lateral heat is minimal. In simple terms, all of the heat is out in front, so practically no heat is generated on the sides. Multicell technology provides precise, stable flame sizes, with well-documented temperature accuracies of ±1°. Use of microscopic flames for very small connections is common with equipment running 24/7 or in a "lights out" facility (see Fig. 1).
Benefits of microflame
The soldering industry has had an ongoing discussion regarding soldering vs. crimping, although these two processes are not necessarily "competitive." Both can be used together to significantly improve the quality of the connection needed to meet a customer's tough specific requirement. There are many reasons for using microflame soldering to bond a terminal and wire after crimping.
Microflame soldering increases pull strength significantly, and is often used to meet and ensure the high pull tests such as electrical cords on medical equipment. Sometimes the terminal is not crimped, or because of shielding or other factors, the crimp itself cannot be made as tightly enough to meet the pull test. Occasionally, the wire and terminal used, although both required for the job, are not perfect together for crimping.
Microflame soldering more completely protects against moisture and corrosion. Many aerospace, aircraft, automotive, boating, and military applications have had difficulty with corrosion weakening the joints between terminal and wire, especially in difficult-to-access (closed) areas like those found in airbag connections. The natural solution and perhaps the easiest is to solder, thereby sealing the joint. Even with large terminals, microflame soldering can ensure complete penetration and, when properly integrated, eliminate the possibility of cold solder joints (see Fig. 2).
 FIGURE 2. For large soldered wire and terminal, the solder penetration using the microflame process is thorough. |
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Microflame soldering is useful for pretinning even the smallest diameter wire, or delicate configurations. The process is noncontact; the heat source does not touch the wire, so if properly integrated, even the most delicate microscopic connections can be soldered. There are also wire configurations in which a section of insulation mid-wire is removed, leaving only the bare wire, which can then be tinned for strength and to protect against corrosion.
Microflame soldering can prevent damage or the opening of smaller crimped connections. Conditions that can cause damage or opening including rough handling during servicing or vibrations such as those caused by automobiles, or even by radios, speakers, and voice coils.
Microflame soldering ensures uniform electrical conductivity and eliminates transitional resistance from component to component, often caused by a lack of uniform connection. Microflame soldering improves the joint to move electricity with less resistance, which is important when multiple wires and components are placed into a single crimp (see Fig. 3).
 FIGURE 3. Multiple parts of a component are crimped together and soldered to ensure reliability. |
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Clean and fast
Why would a manufacturer choose microflame soldering over other methods? First, microflame is a noncontact process, allowing greater heating control and uniformity of the solder volume. No contamination or dross results from contact. Solder volumes will always be the same. The process uses an exact uniform temperature, so production results are always repeatable. This is especially important for small or delicate parts.
Second, the microflame solder process is fast, even with high mass or heavy parts. The average cycle time is usually one-third to one-half less than that of a soldering iron or dipping, with superior more uniform joint penetration. Faster processing leads to greater productivity.
Third, the process involves well-controlled and accurate placement of the heat and heating with no drop in temperature like an iron that fluctuates (cold joints). This ensures accurate solder flow and placement, uniform volume, and clean, shiny, uniform, class-one joints (see Fig. 4).
The operational cost of microflame soldering is very low. The maximum cost is $0.19 per hour, which is $1.52 per eight-hour day, or $4.56 per 24-hour day. The maintenance costs are low when compared to bottled gases, irons, lasers, reflow, and ovens. The consumable costs are significantly lower because solder wire is used rather than pastes, preforms, or solder pots.
The microflame process allows flexible, easy adjustments for different parts, from very large to small. The technology enables quick, simple conversions back and forth from one wire/terminal configuration to another, usually soldering at the same speed at which the wire is being cut, stripped, and crimped. The results are repeatable in small or large batches, even if the job is not run for a long time.
It is ideal to solder on the same equipment used for processing wire and terminals. It is also ideal to solder quickly as you process and crimp, instead of soldering with other secondary methods such as dipping or soldering by hand. It would also be ideal if this were fairly inexpensive to do.
The standard practice
Microflame terminal soldering does all three of those desirable things well, which is why there has been a steady increase in requests for the technology. The rules and theory of soldering apply for microflame soldering as they would for any other method. Although the flame is a noncontact heat source, the precise delivery of intense heat into very small areas gives significant advantages in several areas. Operators can alter portions of the soldering process to take advantage of those factors. However, standard practice is as follows.
 FIGURE 4. A high-speed wire-processing machine produces many crimped and soldered wire terminals. |
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The flame is always directed toward the most massive (heat-consuming) object of the parts to be soldered. (Solder always flows to where it is hottest.) The temperature of the part is controlled by the size of the flame, the distance from the part, and the time the heat is on the part. Changing any one of these factors "fine tunes" the heating.
The solder-feed operation is released only when the temperature of the heated parts reaches the flow temperature of the solder. This means a preheat with the flame is applied before the solder. The preheat time, could, in some applications, be only hundredths of a second.
The flame is usually retracted before solder wire is fed to the object. This ensures the solder is melted by the heat stored in the object, and not by the flame heat itself. This procedure ensures (100%) a cold joint cannot be made. However, in many cases there is an overlap of flame and solder. This is often done to shorten a cycle time, and can overlap in movement.
If the flame and solder location and orientation of the part allows, it is best to heat one side of the part (bottom) and supply solder from the other (top). This is one of several "tricks" which would also prevent a cold joint. It is the most common, easiest method to implement in wire-processing applications. A heating overlap on very small parts usually compensates for the heat absorbed by the solder volume itself.
Microflame soldering processes and technology will be in greater demand as electrical systems and connections become more complex. As cost reductions become more critical, specifications become more demanding, and both automotive requirements and voltages increase, so will the need for the microflame.
GARY W. MILLER is senior technical advisor for Spirig Advanced Technologies, 35 Bronson Rd., Stratford, CT 06614-3654. Tel: (800) 499-9933; E-mail: serve4gwm@aol.com.
