The hazards of tin oxide slag and its solutions
Preface
The process of wave soldering, which plays a key role in the quality of electronic products, is essential in the manufacture of electronic products. The characteristics of the process determine that new liquid solder surfaces are exposed to air, inside which the oxygen constantly contacts and reacts with the molten solder in flowing condition, forming tin oxide slag. The main compositions of the tin oxide slag are oxides of alloy solder and large mixture quantities of alloy solder. The continuous formation and buildup of the tin oxide slag on the surface of the molten alloy solder not only affects its flow-ability but it may also contaminate the PCBA board surface, directly affect the quality and reliability of the soldered products and cause enormous waste of the alloy solder etc.
Lead-free solder alloy with high tin content is gradually replacing the traditional alloy solder Sn63/37, with the introduction of the lead-free soldering in the manufacture of the electronic products. The Sn content of the lead-free solder is much higher than that of the traditional tin-lead solder. Therefore it is easier to oxidize, produce more oxidation slag (SnO2). The problem of the oxide slag is aggravating, notably the waste rate reaches to 30-50% or above, with the extensive application of the lead-free solder. The quality and reliability of the products soldered are also considerably influenced. How to minimize the formation of tin oxide slag becomes a compulsory course in the electronic manufacturing industry!
I. The hazards of the tin oxide slag
1. It affects the flow-ability of molten tin and the height of the tin surface and the soldering quality;
2. It attaches to the surface of the board and causes defects such as tin spherules on the board surface, and directly affects the reliability of the electronic products;
3. Extra problems in the management on the disposal and transportation of the tin oxide slag that will have an environmental impact to a certain extent.
4. Loose oxide slag facilitates the air staying inside the molten solder, and aggravates oxidation of the solder.
5. Useful metals can’t be completely utilized due to the blockage of the tin oxide slag, which will lead to tremendous waste.
II. The significance of reducing the tin oxide slag
As one of the world's scarcest minerals, the proven reserves of tin are 10 million tons globally based on the proven data in 1993. It can be mined continuously for 55.5 years at the exploiting rate of 180 thousand tons per annum；the tin reserves can be mined for 29.6 years in China. The global proven reserves of valued tin metal were 7.12 million tons in 2008! The metal of tin, belonging to a scarce resource, has extensive applications. Tin is a green and environment friendly metal that has been listed as a strategic reserve by various countries in the world. The environment-friendly concept in the metal resources embodies that tin can substitute lead in the solder, and can substitute antimony, lead and cadmium etc in chemical materials. And no substitutes of tin were found currently in solder, tinplate, glass, ceramics gloss etc. The annual demand of the tin is increasing at the rate of 5% (conservatively estimated) under background of the stable growth in electronic and chemical industries and globalized environmental protection. The tin, a very scarce resource, will be used up in about 20 years, based on the data of 360,000 ton consumed globally in 2006, if there are no new great discoveries of tin resource. Those who own tin resources for 20 years shall enjoy wealth that can match holding gold!
The competition in the future is the competition of resources!
Those who own the resources will have pricing power in the future!
The global consumption of tin in 2007 almost equals the high record of 362,000 tons in 2006, according to the preliminary data announced on Tuesday, December 11, in London by the British International Tin Institute (hereafter ITRI). The British organization says: "the global tin consumption in all major applied software have been roughly steady since 2004 except the tin consumption in solder." In other words, the consumption growth of tin since 2004, is mainly manifested the rapid growth in the tin soldering industry.
The futures price of three-month period tin in 2007 had risen by more than 40 percent in LME (London Metal Exchange), the price has doubled since the end of 2004. ITRI data show that the global tin consumption in solder in 2006 accounted for 52% of total tin consumption, 50% higher than that of the last year. Peter Kettle, manager of the statistics and market research department said: "the tin consumption in soldering in Asia accounted for about 80 percent of global tin solder, China alone, accounted 55% of global soldering tin consumption.”
Lead-free solder alloy with high tin content is gradually replacing the traditional alloy solder Sn63/37, with the introduction of the lead-free soldering in the manufacture of the electronic products. The overall manufacturing cost of the electronic products increased sharply with the exponential increment of the unit cost of raw materials and oxide slag of non-lead solder. The electronic manufacturers that have originally fewer profit margins were seriously affected by the soaring prices of the raw materials and labor costs! Meanwhile the quality and reliability of the products generated by the tin oxide slag becomes the major concern of the electronic engineers. The spot price of Yangtze tin listed on Shanghai Nonferrous Metal Net reached to 136,000 RMB yuan (about 18,000 US dollars)/ton in August 2007, however that was 105,000 RMB yuan /ton on 29th June, surged 31 thousand RMB yuan in a month, up to 30%. With the rapid growth of the global tin consumption, tin resources will be used up quickly and the tin price will rise continuously.
Advocating saving energy and lowering consumption on the basis of environmental protection is extremely urgent!
The manufacturing cost of the electronic products can be lowered directly and effectively by reducing of the tin oxide slag of lead-free solder and improving the utilization rate of the lead-free solder; To improve the quality and reliability of electronic products are the simplest and the most direct and efficient measures in enhancing the competitiveness of the enterprises! And it will make great contributions to effectively and reasonably use the global tin resources!!
III.I. Formation of tin slag
1>. The oxidation of static molten solder
According to the theory of liquid metal oxidation, molten metal surface will strongly adsorb oxygen which are decomposed into oxygen atoms and become oxygen ions after obtaining electrons, then combine with metal ions, forming metallic oxides. The whole oxidation of the surface of the molten metal exposed to the air can be completed instantly, forming a layer of single molecule oxidation film, further oxidization need electronic movement or ions transfer through oxidation film, the speed of oxidization of static molten solder decreases gradually; the oxidation of the molten SnCu0.7 is faster than that of Snpb37 alloy.
Pilling Bedworth <1> theory indicates: the compactness and holonomy of the metallic oxidation film, which mainly depends on the volume of the metal oxides being larger than its original volume, is the key of the anti-oxidation. The oxidation slows down as the oxygen atoms are held externally or metallic ions are held internally by the coating of the continuous and compact thin oxidation film on the molten metal surface. The differences in composition and structure of the metal oxide film affect its pattern and the growth rate; when the molten SnCu0.7 and Snpb37 are cooled down from 260℃ under the same conditions, the SnCu0.7 has a rough surface, and the Snpb37 has an exquisite surface. The compactness and holonomy of the SnCu0.7 alloy oxide film is poorer than that of Snpb37 from the angle.
Harvard University Grigoriev Alexei <2> et al put a pure tin sample 99.9999% in the crucible in ultra-low vacuum and heated it to 240℃, and then injected pure oxygen and observed the oxidation of molten Sn via X-ray diffraction, reflection and scattering. They found the molten solder has oxidation-proof ability when the oxygen pressure is low. Oxidation begins when the pressure reaches to the range of 4 x 10-4Pa to 8.3 x 10-4Pa. the growth of “little islands” on the surface of molten Sn can be observed at the partial pressure boundary of the oxygen. These islands are covered with rough surfaces and signals reflected from X-ray mirror of clean tin surface consistently decrease, this kind of phenomenon can prove the existence of oxidation fragments. The X-ray diffraction patterns of surface oxides don’t match with any known Sn oxides and only 2 Bragg peaks occur, its scattering phasor is √3/2, and a face-centered cubic structure can be observed clearly. The surface structure of the molten Sn is scanned by the tangential incidence scanning (GID) and compared with tin oxides already known. That is to say that the phase structure of oxides of molten tin under the pure oxygen of certain temperature and pressure is different from that of SnO or SnO2.
In addition, the standard free energies of formation of SnO2 and PbO under different temperatures are different, the former can form easier thanks to its lower free energy of formation, it also analyzed in a certain extent why oxide slag are increased greatly after the adoption of lead-free solder. Table 1 lists the Gibbs free energy of oxide-formation. We can find that SnO2 can form more easily than other oxides. Usually the oxide film of the static molten solder is a mixture of SnO2 and SnO.
Oxides can partially dissolve into the molten solder as per distribution law, meanwhile the dissoluble difference drives the metal oxides diffuse internally, the gradually increasing oxygen content of the internal metals deteriorates the quality of the solder, this can explain in a certain extend why the metal alloys that refined by high temperature (or called reduction) oxidize easily and generate more slag; The differences in composition and structure of the oxide film, will affect its growth rate and mode, and distribution factors of the oxide in molten solder will have big difference, which is closely related to the compositions of the solder. In addition, oxidation also relates to parameters such as temperature, partial pressure of oxygen in gas phase, absorption of oxygen by the molten solder and decomposing speed, chemical reactivity of superficial atom and oxygen atom, compactness of surface oxide film, dissolubility and diffusivity of the products etc.
Table 1 Standard Gibbs free energies of different oxides
|
oxide |
△G０f.T(O原子)/(KJ/g)
△G０f.T(O atom)/(KJ/g) |
|
298K |
400K |
500K |
600K |
|
PbO |
-188.8 |
-178.8 |
-168.7 |
-159.5 |
|
SnO2 |
-260.1 |
-249.7 |
-239.7 |
-228.8 |
|
CuO |
-129.4 |
-119.7 |
-111.0 |
101.7 |
|
Ag2O |
-10.5 |
-3.8 |
2.5 |
8.8 |
2>. Dynamic oxidation of molten solder
Double waves are widely used in wave soldering, i.e. the first wave peak is the turbulent peak, with narrower width, molten solder flowing faster; the second wave peak is laminar flow wave that looks like flat mirror, stable and slow in flow of the molten solder. New molten solder on the surfaces of the wave continuously contact with oxygen, forming oxide slag as the molten solder flow rapidly. The oxide slag that formed dynamically, have the following three forms and have big differences compared with the static oxidation:
a. Superficial oxidation film, oxidation of the molten solder is undergone in the tin stove at high temperatures via its surface exposed to air interacting with oxygen. The tin oxide film, an epithelial membrane mainly composed of SnO, is primarily formed in the relatively static surface of the molten solder in the stove. As long as the molten solder surface is not destroyed, it can play a role in insulating the air and prevent further oxidation of the internal solder within the protective layer. The superficial oxidation film accounts 10% of the oxide slag.
B. Black powders These powders are big in size and generated in the surfaces of molten solder and in the boundary of the axle shaft, they are roundly distributed and buildup near the shaft. The temperature of the molten solder near the shaft is not higher than other areas thanks to the better heat-transferability of the molten solder although there are frictions between high-speed rotation shaft and molten solder. The formation of black powders are not caused by temperature rising generated by frictions, but caused by vortex of molten solder around rotational shaft, the oxides move with the frictions and spherulize. Meanwhile the frictions can increase the superficial energy of the solder particles and aggravate oxidation that generate oxide slag; accounts about 20% of the total.
C. Oxidation slag Severe mechanical mixing effects exist in the mechanical pump wave generator. Acute vortex movements are being formed in the groove of the molten solder, which are aggravated by rolling motion due to unreasonable design. These movements of vortex and rolling continuously absorb the oxygen in the air and facilitate it entering the molten solder. A lot of silvery sand type oxide slag (or shoddy soybean curd residue) is formed within the molten solder due to limited oxygen absorption that can not fully oxidize as the surface oxidation. More slag formed and oxidation occur within the molten solder, then float to the surface of the molten solder or even occupy most parts of the groove, obstructing pump chamber and channels and then continuously lower the height of the peaks or cause damages in impellers or shaft of the pump. Another type of the slag is formed by the enhanced contacts between solder and oxygen in the air and oxygen absorption generated by acute vortex inside the molten solder swirled by the wave peaks refluxing to the groove. The said two types of slag account 70% of the total and cause huge losses. Application of lead-free solder will generate more oxide slag, and slag from SnCu solder are more than that of SnAgCu, with a typical structure of 90% metal and 10% oxide.
Japanese scholars Tadashi Takemoto <3> et al had carried out tests on SnAg3.0, SnAg3.0Cu0.5 and Sn63Pb37 etc, and found that the weights of slag of all three solder were increased linearly and the growth rate of the said three slag were nearly the same, that is to say the growth rates had less correlations with the compositions of the solder. The formation of oxide slag related to molten fluid flow, solder fluid instability and waterfalls effects may cause absorption of oxygen and rolling of molten solder etc that can make oxidation of oxides slag becoming more complicated. In addition, from the angle of the process, factors influencing the formation of oxide slag include the height of wave peak, soldering temperature and atmosphere, the wave soldering interference, types and purities of alloys or types of soldering agents, the multitude of wave passing through PCBA and the quality of original solder etc.
I. Structure of the tin oxide slag
The tin slag we usually talk about is mainly composed of oxide SnO2 (i.e. tin grey) and Sn wrapped in the tin oxides and little carbonized substances. The tin wrapped in the tin oxides accounts at least 50% or above 90% of the total (the specific contents depend on the slag removed).
The oxide tin in the tin slag (i.e. tin grey) is usually SnO2, grey powder, tetragonal, hexagonal or orthogonal crystals, with a density of 6.95 g/cubic centimeters, melting point of 1630 degrees Celsius; its structure: O:SnO, molecular weight: 150.69, it sublimes from 1800-1900 degrees Celsius; it is hardly soluble in water, alcohol, dilute acid and alkali; it can be slowly soluble in hot strong alkali solution and decompose, and co-melt with strong alkali forming stannate; it can be soluble in strong sulfuric acid or strong hydrochloric acid. Tin content of the slag: 70-90% or up.
V.II. Measures of reducing tin oxide slag
Many research works on reducing the tin oxide slag in the wave peak soldering, have been carried out by domestic and overseas scholars and enterprises. The works are mainly focused on the following aspects:
1>. Nitrogen gas protection
Nitrogen gas protection is an effective measure that uses nitrogen gas to isolate air from molten solder on the reducing of tin slag. The wet-ability of the lead-free solder is weaker than that of the traditional lead-containing solder. Lead-free solder oxides easily. It has become a common technique to carry out soldering under the protection of nitrogen gas.
The oxidation of the lead-free solder obviously decreases with the decrement of oxygen solubility when carrying out soldering under nitrogen atmosphere. The lead-free solder hardly oxidize and the quality of the soldering is better when the oxygen solubility is lower than 50ppm or less. The tin slag can be reduced to about 85 - 95% when the oxygen solubility ranging from 50 to 500ppm.
Linde Company launched SOLDERFLEX®LIS wave oven inert gas protection system, modified the wave soldering equipment, i.e. put the stainless steel structure grooved for wave peaks into the soldering pool, and install many gas spraying pipes and gas control panel etc so as to control the formation of the slag by directly spraying the inert gas to the places where slag may form easily. It is said that the oxygen content in the soldering zone can be controlled within 100ppm and the oxide slag can be reduced 50-80%.
The relative difference on the slag reduction of the different types of alloys is not big according to data provided by Claude Carsac <4> et al. Table 2 lists the study results of foreign scholars <5>.
Table 2 Contrast on the slag formations between atmospheric condition and nitrogen gas protection <5>
|
Types of alloys |
Formation rate of oxide slag（grams/hour） |
|
Under atmosphere |
Under nitrogen gas protection |
|
ITRI lab |
commercialized wave peak soldering equipment |
ITRI lab |
commercialized wave peak soldering equipment |
|
SnCu0.7 |
28.7 |
908 |
1.68 |
45 |
|
SnAg3.5 |
22.8 |
721 |
1.21 |
36 |
|
SnAg2Cu0.8Sb0.5 |
19.8 |
626 |
0.98 |
31 |
|
SnIn20Ag2.8 |
|
800 |
|
40 |
Nitrogen gas protection also brings disadvantages, which mainly are the forming of tin spherules on the surface of PCBA and increasing operation cost. The value of the tin saved can’t offset the cost of purchasing liquid nitrogen or the operating and maintenance cost of the nitrogen generator. However full considerations shall be taken on whether there are savings or not based on the soldering quality while using expensive lead-free solder. In summary, careful calculation and consideration shall be taken before the adoption of the nitrogen gas protection.
2>. Researches on the electro-magnetic pump and its application
Severe mechanical mixing effects might exist if the mechanical pump wave generator is poorly designed. Acute vortex movement and rolling of molten solder speed up the absorption of oxygen. Lots of slag are formed with the continuous absorption of the oxygen into the molten solder and then built up on the surface of the molten solder. In 1969, Swiss scholars R.F.J.PERRIN put forward a new scheme of transferring molten solder by electromagnetic pump. The Switzerland KRISTN company, adopted the technology and firstly manufactured the serial products of single-phase AC transmission electromagnetic wave soldering machine (6TF series) in middle of the 1970s, France also applied patents of similar technology in 1982. In the late 1980s, No.20 Research Institute affiliated to China Ministry of Electronic Industry invented and manufactured a prototype of single-phase inductive melting metal electromagnetic pump, finding a new way of wave peak soldering equipment in molten solder wave power technology development. The rotating parts of the mechanical pump (including electric motor) are removed, it made progress technically by removing the transmitting currents and its generating system compared with the transmitting electromagnetic pump invented by Swiss scholars.
There are two types of electromagnetic pumps, i.e. single-phase or multi-phase induction. It has the following advantages:
a. Never worn-out, long life, easy maintenance.
b. Smooth wave peaks, the oxidation of the molten solder lowers and it can automatically offset voltages of the grid.
c. Comprehensive utilization of energy and high efficiency.
d. Good dynamic characteristics of wave soldering.
e. Low temperature drop in wave soldering.
Disadvantages: same fluid instability and falls effects similarly exist. The electro-magnetic pump is not widely used as the mechanical pump thanks to no-reduction of tin slag formed by the said phenomena and currently high price.
3 > Researches on tin slag separation device
Cookson Company developed a device that can remove the slag automatically. It is called a device of tin-reduction. The specially designed nozzles guide molten solder to designated points and the plasma automatically removes the oxide slag to the collector under which there is hot rolling drum that can collect and compress the oxide slag. The separated and useful solder are collected and guided to hot oven, finally forming for reuse. The useless slag of SnO2 (namely tin grey) are piled up in the container for removing and recycling. It is said the efficiency of the device is 80% higher than manual operation. Japanese scholars Tadashi Takemoto <3> et al developed a tin slag separation and recycling device that is attached to the tin stove. It is enough for the tin oxide slag separation system (OSS) works half hour while wave peak soldering machine works 8 hours. The device can halve the amount of the oxide slag.
Senju Corporation of Japan launched a new type equipment of solder recovery, its principle is to put the oxide slag into the equipment and heat it, then add specially processed sesames, and then mix and stir it, the sesame oil will reduce the oxide from the slag and the oxide reduced is absorbed upon the sesame, separating the solder from oxides.
In addition, tin slag separators based on mechanical stirring are developed by manufacturers in Japan and Hong Kong. Domestic manufacturers launched tin slag reducers based on chemical effects, it is said the reduction rate of tin slag can reach 80%.
This equipment belongs to the off-line separation that uses physical methods. It is impossible to reduce Sn from the oxidized slag SnO2. The so-called tin recovered are the pure tins entrained in the slag. High temperature, pressure and frictions in the reduction equipment can facilitate the re-oxidation of the pure tins; Part of oxides can dissolve into the molten solder as per the distribution law while the dissolubility difference promotes the internal diffusion of the oxides. The gradual increment of oxygen progressively deteriorated the solder. Most manufacturers are using Phosphorus element to improve its anti-oxidation properties, the antioxidant within solder alloy is used up after high-temperature separation (or reduction), therefore the solder processed in this way oxidize easily and can produce more slag; It occupies space, needs special operation, power consumption, high noise etc, its processes of removal, transportation, storage and reduction etc are complex, increasing the management cost. Directly exchange tin bars from manufacturers is acceptable when the reduction rate of tin is not high per se after deductions of expenses such as space rentals of the equipment and warehouses etc, salary of staff members, electricity fees and investment on equipment etc! The feasibility of using such equipment that can generate secondary pollution and also consume electricity, will be questioned when the supply of the electric power is tense.
The above-mentioned methods are to separate pure tin Sn from oxide slag on a physical separation principle. The said methods cannot reduce Sn from the oxidized SnO2 despite it can lower the formation of oxide slag in a certain extent. And the tin separated under higher temperature oxidize easily and generate more oxide slag. It cannot achieve the aim of saving money when the relevant costs are deducted. Therefore, most electronic products manufacturers are seeking chemical products that can be anti-oxidant and can also recover Sn from the SnO2.
4> Use of antioxidant solder
Japanese scholars Tadashi Takemoto <3> et al. had carried out studies by adding Phosphorus and Ge elements into the solder such as SnAg and SnAgCu, its chemical compositions are listed in Table 3. The equipment is a little wave peak tin stove than can hold 15 Kg tin and the test temperature is 250 °C. Test results show that: the weight of tin oxide slag increases with time linearly; the weight of the oxide slag can be effectively reduced after adding small amount of the Ge and Phosphorus elements, of which the addition of Phosphorus element can lower the weight of slag at about 50%; Chemical analysis of oxide slag show that Ge accounts 2-9% of the trace elements added and the P is 4.5 times more. The main content of oxide slag is SnO, 90% of the oxide slag are of metal when the oxygen content is about 5%.
Table3. Chemical Compositions of the various solder alloys
|
Composition |
Abbreviation |
Element Mass Percentage（%） |
|
Ag |
Cu |
P |
Ge |
other |
Sn |
|
SnAg3.5 |
SA |
3.56 |
|
|
|
|
Bal |
|
SnAg3.5P0.003 |
SA30P |
3.48 |
|
0.00325 |
|
|
Bal |
|
SnAg3.5P0.006 |
SA60P |
3.50 |
|
0.006 |
|
|
Bal |
|
SnAg3.5P0.01 |
SA100P |
3.48 |
|
0.0092 |
|
|
Bal |
|
SnAg3.5Ge0.05 |
SA5Ge |
3.50 |
|
0.050 |
|
|
Bal |
|
SnAg3.5Ge0.1 |
SA10Ge |
3.51 |
|
0.090 |
|
|
Bal |
|
SnAg3.5Cu0.7 |
SA7C |
3.48 |
0.71 |
|
|
|
Bal |
|
SnAg3.0Cu0.5 |
SA5C |
3.04 |
0.53 |
|
|
|
Bal |
|
SnAg3.0Cu0.5P0.004 |
SA5C40P |
3.03 |
0.5 |
0.004 |
|
|
Bal |
|
SnAg3.5Cu0.7Ge0.05 |
SA7C5G |
3.51 |
0.67 |
|
0.049 |
|
Bal |
|
SnAg3.5Cu3.50.7Ge0.1 |
SA7C10G |
3.5 |
0.68 |
|
0.1 |
|
Bal |
|
SnCu0.5Ag0.3 |
SCA |
0.34 |
0.49 |
|
|
|
Bal |
|
SnCu0.5Ag0.3P0.004 |
SCA40P |
0.34 |
0.49 |
0.004 |
|
|
Bal |
Certain results have been achieved by domestic scholars, who had also studied and proposed methods of adding various micro-elements such as TI, Ga, Re, Sb, In, Ni etc into different solder alloys so as to lower the formation of oxide slag. At present lead-free solder used in domestic wave soldering industry are mainly SnCu and SnAgCu, most manufacturers are adding P element to improve its antioxidant properties, but the anti-oxidizing effect will gradually invalidate with the extension of time and consuming of trace elements. Therefore the anti-oxidation reductants appear!
Researches on the tin slag reductant (powder) and its application
The formation of oxide slag is tightly related to the flowing behavior of the molten solder. The more unstable and perturbative the fluid, the easier the absorbing of oxygen that leads to form more slag. So far, the mechanism of the slag mixture formation in wave peak soldering is not clear. It is better to select equipment featuring reasonable design in fluid jet system, less formation of slag and easy removal of slag etc and combine with anti-oxidation-reduction agents of higher performance-price ratio for enterprises that use wave peak soldering, so as to finally minimize the losses caused by oxide slag (SnO2) and achieve higher economic benefits.
The antioxidant microelements within lead-free solder are used up rapidly and the solder quickly loses its efficacy due to the microelements are inclined to agglomerate on the surface of the solder and can preferentially absorb the oxygen in the air that Sn element. The oxygen- absorption is generated by the instability, falls effects and rolling of the molten solder. Parts of oxides can dissolve into the molten solder as per distribution law, meanwhile the dissoluble difference facilitate the metal oxides diffuse internally and the oxygen contents gradually increase due to various reasons; therefore the most practical and effective measures are to add a type of anti-oxidation reductant so as to immediately reduce the oxide slag formed and prevent its agglomeration as while as hold further formation of oxide slag. Domestic and abroad manufacturers released anti-oxidation reductants (powders) for tin slag (slag of soldering, SnO2, i.e. called tin slag industrially) one after another.
Conditions that anti-oxidation reductants shall possess:
A>. Must conform to the requirements of environmental protection, do not affect working environment of the production site and do not affect the composition of solder alloy.
B>. Reacted residues shall be non-sticky or not fly away, shall not contaminate the surface of PCBA and existing production equipment (such as wave soldering machine etc).
C>. Be non-flammable, noncorrosive, it shall not change the existing production processes, shall not affect routine maintenance of the existing equipment.
D>. The amount of the consumption shall be less, the reduction rate shall be high, easy to handle the residues reacted which shall be biodegradable; it can substantially save energy and reduce consumption for enterprises from the point of view of environmental protection.
A Taiwanese company developed a reduction powder for tin slag. It can mainly absorb various impurities and oxides, avoid oxidation of the molten solder and heat losses. It is said the reduction powder can reduce 95% of the solder oxidation. Its disadvantages are generating huge smoke and having pungent smells. The wave soldering equipment must be modified before using the powder that generates sticky residues after reaction and form hard solids after cooling. It brings some inconveniences to routine maintenance.
American P. Kay metal Fein-Line Partnership Company have developed surfactants that have two functions when it contacts with molten solder: first is forming a protective film on the molten solder surface that can prevent further oxidation, second is the active elements react with the metal oxides that will be dissolved into the surfactants, suspending between metal oxides particles and the remaining surfactants as organic metal compounds. The surfactants are consumed by oxides slag in a smoke-free and odorless way and don’t react with metals until they are used up. When the metal oxides in the slag are dissolved, the arrangements of these interconnected oxides are open, any clip of metal agglomerate and flow back to molten solder. And the compositions of the solder are not affected by the surfactants. It is said the technology can lower 40-75% of the soldering cost. Its disadvantages are of modifications on the soldering equipment that uses the reductant, stickiness of the reacted residues, forming hard solids after cooling, sticking to the equipment and PCBA that are difficult to clean, even the possible plugging to the jet nozzles etc that bring inconveniences to the routine maintenance of the equipment. The performance and reliability of the electronic products may be affected once the surfactants fall on the PCBA board, forming sticky substances that are difficult to remove! And its price is high, the lowered soldering cost equals that of the surfactants.
ICHIMURA JR07 tin slag antioxidant developed by Shenzhen Kunqixinhua Technology Co., Ltd is an organic polymer compound made of many surfactants, wetting agents, dispersing agents etc via scientific methods. It contains no heavy metals, and can dissolve in most parts of organic solvents and in water; it is neutral with pH values ranging from 6-7. Its excellent resistance to high temperature (burning point above 330℃) and volatility (almost non volatile), almost smokeless, odorless, non-sticky, noncorrosive, it also has the function of anti-oxidation and reduction. The amount of consumption is less and its reduction rate is high, notably above 90%. The saving of the solder reaches 38% after deducting the cost of the anti-oxidation reductant, ICHIMURA --JR07 as per assessment report by the FLEXTRONICS Company. Certain high appraisals on the anti-oxidation reductant ICHIMURA --JR07 were given by the companies such as FOXCONN, HASEE, SOLECTRON, PRIMAX, GBM and HUNTKEY etc. This product is featured of simple and convenient in operation, no modification on the equipment and increment of operators are required, reducing tin slag by direct addition and lowering the times and quantities of slag removal, enhancing the production efficiency and utilization of solder, no-changing of effective compositions of the solder and no contamination on PCBA, higher reduction efficiency etc. it has an excellent resistance to high temperature and volatility, its residues are non-sticky, fragile, dissoluble in water and biodegradable. It can’t sink into crock bottom. There are no worries about plugging in nozzles and impellers. It brings convenience in routine checks and maintenance only needs wiping with wet cleaning clothes.
The anti-oxidation-reductant ICHIMURA - JR07 for tin slag, can separate the tin wrapped by oxide slag and reduce tin (Sn) for further use from tin oxides (SnO2); and the effective compositions preferentially combine with the oxygen in the air the Sn element, which obviously lower the O2 content inside the solder, prevent further oxidation of the molten solder, enhance the flow-ability of the molten solder and effectively improve the PCBA soldering.
The product had completely passed relevant tests and accreditations by SGS, SIR, MSDS, STIR and CHIPS etc
Its reduction process of the oxides can be roughly expressed as: O2 + R = OxRx; PbOx + R = Pb + OR (1); SnOy + R = Sn + OR (2): where PbOx represents for the lead oxide, R for liquid reductant, and Pb for lead reduced, OR for oxides, SnOy for tin oxides, Sn for tin reduced.
Liquid covered chemical replacement reaction of reduction was successfully adopted in regeneration process of the anti-oxidation reductant, in ICHIMURA-JR07. The reductant is made from non-toxic and biodegradable organic materials. No harm to humans and the environment can be imposed by the reductant and its oxides. The liquid covered process of waste soldering treatment has a relatively lower temperature, notably under 280℃, which is far lower than the temperature (above 400℃, the temperature of the tin reducing device) that can generate lead smoke; on the other hand the surface covering of the liquid reductant can effectively restrain the escaping of the lead smokes; The solubility of the product in water determines it contains small amount of water that can be seen as less steam vapor in soldering; therefore it not only reduce the lead-tin oxides in the slag but also effectively avoid the environmental pollution caused by residues and lead smokes.
Advantages of the ICHIMURA - JR07, tin slag anti-oxidation reductant:
1. Water-soluble, non-flammable, non-corrosive, non-sticky, almost smokeless, odorless, do not contain any heavy metal components; it does not change the effective ingredients of solder.
2. No chemical reaction with scaling powder; No contamination on PCBA
3. It can reduce the oxygen content of the molten solder, increase liquidity and wett-ability of the molten solder, effectively help PCBA soldering,
4. It do not contain any forbidden materials: PFOA+PFOS+SB, azimino-benzene, TBBP-A, asbestos, formaldehyde, in accordance with ROHS and REACH.
5. Its reacted residues is muddy, non-sticky, soluble in water etc facilitate routine maintenance of the equipment; save energy and reduce waste for enterprises.
6. The reduction rate is high, 1KG JR07 can reduce 30-50KG tin slag, reducing time is long, it can holds 4-6 hours for one time adding, and reduce man-power operation.
7. It have pass SIR, electromigration, slice up tests, it’s a real environmental protection and energy-saving product. (Have export to Hungary, India, Thailand, Malaysia, Singapore, Israel, and Taiwan and so on. )
References：
1〉The Corrosion and Oxidation of Metals, written by UR Evans Publishing House of Machinery Industry, Beijing 1976.
( 2005) 223- 232.
2〉Alesei Grigoriev, etc. Surface oxidation of liquid Sn. A.Grigoriev et al Surface Science 575 ( 2005) 223- 232.
3〉Tadashi Takemoto,Yeon Jun Joo,Shohei Mawatari,Rikiya Kato .Reduction of dorss formation during wave soldering using lead-free solder 0-7695-1266-6/01﹩10.00 2001IEEE.1131-1136.
4> Claude Carsac etc, Inert soldering with lead-free Alloys Review And Evaluation [R].IPCSMEMA Council APEXSM 2001.
5> C.Carsac, J.Uner and M. Theriault Inert soldering with lead-free alloys: Review and Evaluation. IPCSMEMA Council APEX 2001:3-7.
Nobeyan
On June 16th, 2008
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