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Lead-free welding technology process
Electronic product manufacturing resonant process need to face the following problems; 1) utilizing lead-free solder; 2) components and PCB utilizing; 3) utilizing of welding equipment
1) utilizing lead-free solder
So far, lead-free solder composition have been reported all over the world has nearly hundred kinds, but the real and recognized by industry
Is widely used as Sn Ag - Cu ternary alloy, there are also various alloy, add In, Bi, zinc and other elements. At this stage the coexistence of a variety of lead-free solder alloy on international situation, brings to the electronic product manufacturing costs increase, appear different requirements of customers of different solder and different technology, the development trend of the future will tend to the same alloy solder.
(1) high melting point, higher than the Sn, Pb, about 30 degrees;
(2) the ductility decreased, but there is no long-term degradation problems;
(3) the welding time is commonly 4 seconds;
(4) the strength of tensile strength in the early and late strength is superior than that of Sn, Pb eutectic.
(5) the fatigue resistance is strong.
(6) on the flux of higher thermal stability requirements.
(7) high Sn content, high temperature of Fe strong solubility
Given the nature of the lead-free solder determines the new lead-free welding technology and equipment
2) resonant components and PCB
In lead-free soldering process, the components and PCB plating resonant technology is relatively complicated, involving fields widely, and this is the international environmental group delay resonant process, one of the reasons for a period of time, lead-free solder PCB plating coexist with Sn, Pb, and "stripping (Lift - Off)" welding defects, such as equipment manufacturers have to overcome this phenomenon from the device. In addition to the requirements of the PCB production process is also relatively improve, PCB and components of the material requirements better heat resistance.
3) utilizing of welding equipment
Due to the particularity of lead-free solder, lead-free soldering process requirements for lead-free welding equipment must be solved and lead-free solder welding defects of solder on the equipment, the influence of preheating/tin stove temperature, nozzle structure, oxide, corrosion resistance, rapid cooling after welding, flux coating, nitrogen protection, etc.
A) lead-free welding required temperature curve analysis:
Through the graph and the metal material science knowledge, we know that in order to obtain reliable and best solder joints, best value should be greater than the temperature T2 lead-free solder eutectic temperature, liquid tin soldering temperature control in the 2500 plus or minus 20 degrees c (more strict than the temperature of the pewter), generally have high reliability requirements of military products, delta T < 300 c, for ordinary civil products, it is recommended that the temperature difference can be relaxed to delta T2 < 500 degrees (according to the requirements of Japan panasonic); T1 is slightly higher than lead welding preheating temperature, concrete numerical value according to the flux and PCB process and so on to decide, but delta T1 must be controlled within 50 degrees, to ensure that the flux of activation and give full play to improve the performance of solder invasive; After welding cooling from temperature T32500 fell to temperature T4100 ~ 1500 degrees, suggested by 10 ~ 150 degrees/S drop gradient control; Temperature curve on the time requirement is mainly preheating time t1, immersion tin time t2, t3, t4 and cooling time, the time the determination of the specific numerical want to consider the heat resistance of components, PCB and solder the specific factors, such as t1 in 1 minutes, usually the t2 + t3 between 3 ~ 5 s.
B) from the above temperature curve analysis can determine the structure of the equipment and the control requirements:
Preheat the way
Preheat time t1 in 1 minutes delivery PCB at a speed of 1.2 m/min, preheating length to ensure more than 1.8 m; In order to guarantee the thermal stability of the preheat preheat structure must adopt closed structure, preheating method recommended: 1) hot air preheating way; 2) way of far infrared heating tube; 3) ceramic heating tube (or stainless steel heating tube). From the wave soldering equipment factory developed at home and abroad, and customers to use analysis, adopts 1 kind of hot air preheating method is more ideal, because the heating principle is a kind of like reflow furnace heating principle, which can effectively prevent PCB by sudden thermal shock and improve the thermal efficiency, good effect, safe and reliable, and avoid rosin before dripping ON the heating tube caused by fire, the resultant force in shenzhen xin company production of 1000 sets of equipment for use this way (since 2001), especially for lead-free wave soldering and develop a new control method: PID + analog voltage regulation mode, solve the impact of the traditional way ON - OFF control ON temperature, achieve better preheating curve, guarantee the preheating zone and welding of the temperature drop of value within 50 degrees. Preheat divided into 3 zones length 1.8 M, welding preheating process will be flexible. Of course for some products for a far infrared heating tube way.
Tin furnace nozzle
To overcome poor wettability of lead-free solder (spread out) for welding defects, need more than 4 seconds time of immersion tin, if with double wave soldering, the minimum temperature between the two peaks to above 2000 degrees tin furnace nozzle structure must be able to meet the above temperature curve, equipment manufacturer by widening nozzle design, reduce the two peaks spacing to achieve.
Due to the high content of Sn lead-free solder easier oxidation, in addition the high cost of lead-free solder, control the tin oxide generation is welding equipment manufacturers must consider the question, some domestic and foreign manufacturers have launched a new wave nozzle structure, oxide generation compared to the past to reduce doubled, drink; Resultant force xin's dual wave nozzle structure has been widely applied to many Japanese companies and domestic well-known companies, and recognized by our clients.
corrosive
High Sn content of lead-free solder, at high temperatures have very strong ability to dissolve to Fe, the traditional wave soldering solder slot and the vent most adopt stainless steel material, thus dissolving reaction, with the passage of time, leads to the corrosion damage of components, especially the nozzle and wheel parts. Now most of the overseas manufacturer with cast iron solder bath and coating protective layer, most domestic manufacturers with titanium alloy materials.
Oxygen is changed
Compared with Sn, Pb alloy solder, lead-free solder in high temperature welding high Sn content more easily oxidized, which formed in tin stove liquid surface oxide residue (SnO2), excessive oxide not only affect the welding quality, and the solder cost waste, especially the lead-free solder are expensive now. Most equipment manufacturer USES improved nozzle structure to reduce oxide tin furnace, such as the above mentioned the cologne company of new nozzle. Of course the best countermeasure is to add nitrogen protection, nitrogen protection system equipment upfront investment is larger, if from long-term interests to consider is reasonable. So many equipment manufacturers at home and abroad have been introduced wave soldering, nitrogen protection technology has been mature.
Quick cooling after welding
Under lead-free welding technology application, the stature plate wave soldering defects often occurred "stripped" (Lift - off, or Fillet lifting), the cooling process, the reason is that the solder alloy caused by different cooling rate and cooling rate on the printed circuit board. Utilizing prophase, lead-free solder and coated components of Sn, Pb coexist, there will be a period of time if the Bi lead-free solder containing this kind of phenomenon is more prominent, the solution is in wave soldering and cooling system at the exit, as for cooling and cooling rate requirements according to the specific conditions and decide, because the cooling rate of more than 60 degrees/SEC. The equipment cooling system to adopt cold source, most use cold water machine or air cooler, study abroad is mentioned in cold fluid way, can reach 200 m/SEC. Above the cooling effect, the cost is very high, is unbearable for large-scale electronic products manufacturers, belong to the early experiments, really was applied, most manufacturers in Japan by fully utilizing scheme (such as solder/components/substrate all resonant), equipment cooling structure adopt compulsory natural wind cooling, for domestic manufacturers of electronic products, recommended Sn Ag - Cu alloy or Sn - Cu alloy solder, fast cooling rate control in 6 ~ 80 degrees/SEC. / SEC. Or 8 ~ 120 degrees, use natural wind cooling way forced cooling or machine with cold water cold source.
flux
The particularity of lead-free solder in welding process must be in the corresponding flux, matching based on considerations of environmental protection, low alcohol solvent used, gradually promote the VOC - FREE flux of environmental protection.
Due to poor wettability of lead-free solder, overcome weld defects in the very great degree by flux composition and spray way to change, with traditional foam spray structure has not adapt to the current process, spray some equipment manufacturer, improved structure, some manufacturers of spray mobile adopts stepper motor method, flux supply the equilibrium pressure system, strong convulsions filtration system, the purpose is to make uniform spray effect, reduce the emissions of volatile substances.
control
The developing direction of control system is mainly the digital control and management.
Control system in addition to the requirements of transportation speed, flux coating uniformity, preheat temperature and tin stove temperature and cooling rate on precise control, should also be in the process of production of all process parameters (transport speed, flux coating thickness, density, width and Angle, preheating temperature, tin furnace temperature, cooling rate, nitrogen concentration, etc.) all digital control, parameters for reuse. Cologne's ADS series wave soldering all digital control as the core target, adopts the man-machine interface or industrial control computer to monitor the production process, not only can monitor, PCB parameters and machine parameters, the PID parameters, temperature, also support the parameters setting, open, save, convenient parameter of reuse, minimize model to replace the adjustment parameters of time. On the full computer control models, random comes with lead-free soldering is very concerned about the temperature curve of test and analysis function, can test and analysis of the three temperature curve of preheating, preheat slope, preheating temperature, wave 1 time, wave 2 time, wave 1 temperature, wave 2 temperature, dropping time, dropping temperature, cooling time, cooling slope, beyond time and so on, and support the temperature curve, print, functional testing, lead-free welding of all parameters can be clear at a glance.
Another direction of the development of the control system is a customer cost concept.
Customer cost refers to the production of a certain number of products in production process consumption of materials, time, energy, etc. Resultant force xin company's products always follow the principle of utmost reduce customer costs, the flux consumption, reduced the volume of solder oxide, power loss, the aspects of nitrogen loss comprehensive control, to achieve the purpose of saving the cost of customer. Manufacturer of solder, or production equipment manufacturers, the products should conform to the welding process and balancing the costs of the end user, with the development of technology, lead-free welding process will be gradually maturing,
JOINT XIN company with many years of cooperation, both at home and abroad for the above features developed is suitable for the special double crest welder WS series of lead-free requirements,, and has been beautiful, SANYO, jia, XuDong sakata and other Japanese companies and adopted by domestic and foreign well-known companies. Technology has reached the international level, and exported to international markets.
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