1. The evolution of wave soldering technology and lead-free applications

 

  1. Evolution of wave soldering technology

 

Wave soldering is a mature technology and an efficient large-scale soldering process that has been widely used in the production of electronic products and remains so today. However, the discreteness and complexity of wave soldering control parameters also make people find it very difficult. The complexity of wave soldering is specifically reflected in the diversification of process variables, such as conveying speed, flux chemical composition, preheating temperature, solder tank temperature, PCB design, solderability of components, PCB and soldering during the soldering process. The interaction of material waves, equipment maintenance and operator training, etc.

 

 

 

Although many test carriers have been designed to evaluate SMT placement capabilities and reflow soldering process operations, there is still no comprehensive and statistically convenient test carrier suitable for SMT devices in the wave soldering process. This also fully illustrates the variability and complexity of the wave soldering process.

 

 

 

Wave soldering technology is constantly being improved and improved in its application, with the goal of producing perfect wave soldering joints in the first time. Repairs will not improve the quality of the original solder joints, and repairs to any solder joints will degrade the quality of the solder joints because they will undergo another temperature cycle, which will increase the thickness of the intermetallic compound.

 

 

 

From the perspective of technological development, the extensive application of narrow-pitch QFP, area array packaging devices BGA, CSP, and FCOB has made the reflow soldering process more and more dominant in the interconnection between devices and PCBs. Although this does not mean that the wave soldering process has disappeared, it does make it gradually withdraw from its original dominant position.

 

 

 

Judging from the current situation, through-hole assembly still occupies a certain proportion in some lower-level electronic products. The main reason why this state persists is that many occasions do not require the higher performance of SMT technology. In this case, through-hole assembly is undoubtedly a low-cost solution and is therefore continued to be used. Therefore, wave soldering technology still occupies a mainstream position in the production of such products.

 

 

 

   2. Technical characteristics of lead-free wave soldering

 

With the continuous growth of lead-free production of electronic products, the current reflow soldering process has shifted its focus to lead-free processes, which drives the wave soldering process to also be converted to lead-free technology to avoid lead-containing solder on the same component. Mixing with lead-free solder will cause unnecessary trouble.

 

 

 

If the lead-free wave soldering process is to be successful, changes to the entire process must be considered. Although most lead-free solders have good solderability to the base metal, compared with tin-lead solders, they exhibit reduced wettability. Since wettability is a critical factor in welding and is affected by multiple variables, these changes will affect most machine parameters.

 

 

 

The technical characteristics of lead-free wave soldering are mainly reflected in the following aspects.

 

(1) The melting temperature range of the solder used is generally high.

 

At present, the solder alloys for lead-free wave soldering with good application performance and low cost mainly include Sn-Cu, Sn-Cu (Ni), Sn-Cu (Co), Sn-Ag-Cu (such as SAC305), etc. Its main process temperature characteristics are shown in the table below

 

 

For example, the welding temperature of SAC305 solder is 255~265℃, while Sn-0.7Cu requires 265~270℃, and 275℃ is also selected. However, as the welding temperature increases, the operating temperature window available for selection will also narrow due to the limit temperature limit of thermal damage to the PCB substrate and components. In order to ensure the reliability of welding, it is necessary to first determine the appropriate contact time with the molten solder when the minimum temperature to obtain good wettability is above 240°C.

 

 

 

Excessive temperature not only has a great impact on the reliability of PCB and components, but also increases the corrosion of the solder tank, as shown in the figure below. Fe melts into the lead-free solder to form iron-tin crystals, which will increase the viscosity of the solder and affect the fluidity of the solder.

 

 

(2) Poor wettability

 

   The wettability of lead-free alloys is generally worse than that of Sn-37Pb, as shown in the figure and table below.

 

 

 

(3) Oxidation is more serious during welding

 

Lead-free solders popularized in industry are basically composed of Sn, Ag, Cu and other elements. The most common main oxides in Sn-Pb alloys are SnO and SnO2; in lead-free solder, not only the Sn content is higher, but other added elements such as Ag, Cu, etc. are also very reactive to oxygen, so the work More and more complex oxides and more solder slag will inevitably be formed. Chemical reaction kinetics tells us that for every 10°C increase in temperature, the rate of chemical reaction will double. The increase in lead-free wave soldering temperature further aggravates the formation of large amounts of oxide slag. Some foreign scholars claim that the amount of solder slag produced during lead-free wave soldering operated in air will be 5 to 7 times greater than that of Sn-37Pb, and 70% to 85% of the welding cost will be spent on solder slag. superior.

 

(4) Traditional solder wave generators face serious corrosion problems

 

Sn is corrosive to the solder tank at high temperatures, so high Sn-based lead-free alloys will cause corrosion of structural metal parts such as pumps, guide plates, and solder tanks. For example, rust spots often appear on the surface of stainless steel or cast iron, and obvious corrosion will occur after being in contact with lead-free alloys for a longer period of time, as shown in the two figures below. If it contains Ag, it will accelerate the corrosion process.

 

 

Erosion of Fe-based alloys by Sn-based alloys

 

 

Sn’s corrosiveness to the solder tank

 

The solder pump, guide plate and nozzle in traditional wave soldering equipment will frequently wear out when used in lead-free soldering. The iron element in stainless steel will dissolve in the solder to form FeSn2 crystals (as shown in the figure below). This crystal has a melting point as high as 510°C and will remain in the solder. Since the solder flow rate is slower at the corners of the solder tank, crystals usually accumulate in these corners. If these crystals are pumped out with the solder, the crystals may remain at the solder joint causing bridging. Therefore, people have to consider replacing corrosion-resistant materials, such as nitrided steel, titanium, ceramic coatings, and titanium alloys, to manufacture turbines, guide plates, and solder nozzles to meet the long-term application requirements of lead-free solder.

 

 

(5) Cu pollution will become more serious

 

The temperature of lead-free soldering is much higher than that of Sn-Pb solder, so the Cu on the PCB pad and component pins is dissolved much faster, as shown in the figure below.

 

 

The dissolution rate of Cu in solder

 

 

 

        As the Cu content in the solder increases, the wettability of the solder and the corresponding welding temperature will change (as shown in the figure below). The excess Cu6Sn5 formed will contaminate the solder in the solder tank.

 

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Effect of increasing Cu content on wettability and welding temperature

 

 

 

(6) The welding defect rate will increase significantly

 

Due to the high surface tension and poor scalability of lead-free solder alloys, welding defects such as solder beads, bridges, virtual soldering and poor through holes will increase. This will directly affect the quality, reliability and manufacturing pass rate of solder joints, and the requirements for welding process design will also be more stringent. For example, the soldering temperature will directly affect the through-hole filling effect. As shown in the figure below, the filling effect of SAC305 solder at 240°C, 250°C, and 260°C respectively.

 

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Effect of soldering temperature on through-hole porosity

 

 

 

(7) Requires the use of high boiling point flux

 

Due to the higher process temperatures, lead-free wave soldering requires the use of different high-boiling point solvent fluxes than lead-based wave soldering. The flux type will determine which preheat configuration is best for the process.

 

 

 

At the same time, the activity and thermal stability of the flux must be optimized to reduce the soldering defect rate and ensure the filling ability of the through holes.

 

(8) The influence of welding environment atmosphere on the quality of solder joints

 

Compared with tin-lead solder alloys, most lead-free alloys will oxidize quickly when the solder liquefies due to the increased Sn content. Due to the high temperature of the welding process, oxides and dross composed of SnO and SnO2 will quickly form during the working process.

 

 

 

Using N2 in the solder tank area can minimize the exposure of the liquid solder to the O2 atmosphere, thereby reducing solder oxidation, improving wettability, improving welding performance, and reducing welding defects. N2 also reduces oxidation of boards and components to compensate for the poor wettability of lead-free solder. Taking Sn-Cu lead-free solder alloy as an example, under the protection of N2 atmosphere, the time to reach the maximum wetting force is significantly reduced, as shown in the figure below.

 

 

Maximum wetting power

 

 

 

The following figure shows the situation of wave soldering without using N2 protection and using N2 protection. The quality of solder joints using N2 protection is obviously better.

 

 

Solder joints without N2 protection

 

 

Solder joints protected by N2

 

 

 

Especially for OSP-coated PCB boards, which have experienced high temperatures several times before wave soldering, the use of N2 is particularly important. N2 can also reduce bridging and tipping, and improve through-hole filling of thicker veneers.

 

 

 

2. Equipment technology suitable for lead-free wave soldering process

 

    1. Flux ultrasonic spray technology

 

Due to environmental protection requirements, alcohol solvents in traditional fluxes are VOCs, and there are increasing calls for their ban. The use of VOC-free fluxes is one of the trends replacing alcohol-based solvent-based fluxes.

 

 

 

Applying the finest possible flux particles with the lowest possible air pressure is key to achieving good through-hole penetration and successful water film evaporation. Higher air pressure settings may cause the particles to rebound and thus will not improve the wetting of the flux to the PCB surface. Obviously, ultrasonic atomization spray is the most ideal choice because it can deliver enough fine flux particles deep into the through holes to improve the porosity of the lead-free solder alloy.

 

    2. Long infrared and hot air composite preheating zone

 

Due to the high melting temperature and poor scalability of lead-free solder alloys, a long preheating zone is often required to reach a higher temperature and avoid overheating of the PCB after loading into the PCB. The top of the PCB reaches the appropriate preheating temperature, which has the greatest impact on reducing welding defects.

 

 

 

During the heating time of the preheating zone, in order to ensure that components with different heat capacities can achieve the same heating effect, it is best to use a composite heating method that uses both far-infrared heating and hot air circulation heating. Combining far-infrared heating from the bottom of the PCB with convection heating from the top of the PCB results in optimal PCB preheating.

 

    3. Adjustment of the structural layout of the solder wave peak generator

 

Because lead-free alloys have poor wetting characteristics, higher soldering temperatures and longer contact times are required. Therefore, in lead-free wave soldering equipment, it is usually necessary to change the structural layout between the traditional wave nozzles, as shown in the figure below. The distance between the two wave peaks should be as short as possible to prevent thermal shock to the PCB due to excessive temperature drop in the middle.

 

 

Increasing the width of the second wave (laminar wave) improves wettability, producing an effect similar to increasing preheating heat. Reduce the height of the laminar flow nozzle from the liquid surface to reduce the lift of overflowing solder, thereby achieving the purpose of reducing the amount of oxidized slag.

 

 

 

    4. The transmission guide rail should add intermediate support

 

Due to the high temperature of lead-free wave soldering and the long soldering time (3 to 5 seconds), the temperature endured by the PCB substrate may far exceed the glass transition temperature (Tg) of the substrate material itself, causing the substrate to become soft and deform and bend downward in the middle. For large-size PCBs, in order to prevent the above phenomenon from occurring, the transmission guide rail should be added with intermediate support.

 

    5. Cooling device

 

Similar to reflow soldering, after wave soldering, it is necessary to prevent the heat from dissipating too slowly on the solder joints. The residual heat will cause the solder joints to be exposed to high temperatures for too long and cause the following defects.

 

① The long solidification time of solder joints caused by high temperature can easily cause the solder crystal grains in the solder joints to grow too much. The increase in coarse grains will lead to the deterioration of the strength of the solder joints.

 

② Causes the welding edge of the solder joint to rise, as shown in Figure 3.15. Its occurrence rate is also closely related to the cooling speed after passing the wave peak, as shown in the figure below.

 

 

The welding edge of the solder joint is lifted

 

 

The relationship between pad edge lift and cooling rate

 

 

 

Therefore, the welding surface of wave soldering equipment should have a faster cooling rate to quickly cool down the solder joints. However, the cooling speed of the component surface must be appropriate. Too fast may cause damage to chip components with ceramic body structure. In addition, when speeding up the cooling rate, care should be taken to avoid affecting the temperature of the solder tank.

 

 

 

  6. Oxide separation system

 

The Sn content in lead-free solder alloy is higher than that in Sn-Pb alloy, and the lead-free soldering temperature is also higher than that of lead soldering. Higher temperatures will cause more oxidation and more solder slag.

 

 

 

Measures can be taken to reduce the amount of solder slag. An axial seal is installed on some wave soldering machines to eliminate the formation of solder slag around the pump shaft, as shown in the figure below.

 

 

 

Other solder slag is formed on the wave crest, and the amount of oxidized slag can be reduced by reducing the drop height of the wave (the distance from the top of the wave crest nozzle to the solder liquid level).

 

 

 

    7. Application of hot air knife (HAK)

 

   As the spacing of device leads decreases from 1.27mm to 0.635mm in SOIC packages or QFP packages, ICs with pin spacing less than 0.635mm are now appearing, such as IDC connector terminals of ribbon cables. In input/output connectors, the large number of terminal blocks with more than three rows also makes welding more difficult. Especially when the plugs and sockets are located at the entrance or exit of the solder wave peak, where the shape of the wave peak is the worst, the welding quality is difficult to guarantee.

 

1) Working principle of Hollis hot air knife

 

  In the early 1980s, researchers from Motorola Corporation in the United States systematically studied the inherent characteristics of solder and solder joints, and proposed an exposure technology to remove bridges and virtual solder joints in wave soldering. Based on the above principles, Hollis Company developed a transverse linear bridge-breaking technology, the so-called Hollis hot air knife system, and obtained a patent.

 

The working principle and structure of Hollis hot air knife are shown in the figure below.

 

 

How the hot air knife works

 

 

 

Hot air knife structure

 

 

 

The application of hot air knife (HAK) can avoid solder bridging. Of course, to be honest, many welding equipment can achieve satisfactory welding quality without HAK. That is due to the better processing level and design capabilities of well-trained employees.

 

 

 

Hot air knife can help solve some difficulties often encountered in PCB assembly. If advanced fine-pitch technology is not used and the defect rate can be stabilized at less than 100ppm, HAK does not need to be used.

 

 

 

The parameters that affect the performance of the hot air knife mainly include: ● The distance from the bottom of the PCB; ● The angle of the hot air knife; ● The temperature of the hot air; ● The pressure of the hot air.

 

2) Bridge breaking mechanism

 

Wendell Hutchinson, a researcher at Motorola Company, concluded after research and experiments that the adhesion force on the solder joints can reach 114 times the cohesive connection force between liquid solder. Apparently, excess cohesive solder (bridging) can be easily removed from the sample, while solder that adheres firmly and directly to the pads and component leads has strong adhesion and surface energy, and It cannot be removed easily. The bridge connection is purely based onThe result of excess solder connected by the cohesion between solders is shown in the figure below.

 

A structural model of bridge points

 

 

PCB surface after HAK

 

 

 

    8. Closed-loop control of solder wave peak height

 

According to the latest international research and test results on the mechanism of wave soldering, the key factor affecting the effect of wave soldering is the interaction between the PCB and the solder wave peak. By improving the interaction between PCB and solder wave peaks and adding the wave peak height closed-loop control function, digital-to-analog automatic control of the wave soldering process can be achieved. This provides a strong guarantee to further ensure the high quality of solder joints and eliminate the interference and influence of human factors.

 

1) Mechanical pump type solder wave peak height closed-loop control

 

(1) Structure and function: The wave crest height control system is designed to maintain the precise height between the transfer guide rail and the solder wave crest. As long as the height of the clamping claw of the welded PCB into the guide rail is constant, the PCB will be in precise contact with the wave crest. can be maintained, as shown in the figure below.

 

Wave crest height sensor

 

 

Installation location requirements

 

 

 

This system invented by the American ELECTROVERT company is called ExactaWaveTM. The system compensates for changes in solder wave crests that may occur due to solder slag accumulation, mechanical instability or poor maintenance. In order to maintain the stability of the wave peak, ExactaWaveTM allows the sensor to be very close to the PCB, so the sensor readings are very accurate, as shown in the figure below.

 

 

 

Positioning of solder peak height sensor

 

 

 

(2) Control principle

 

In the conveying system, the purpose of the ExactaWaveTM system is to control the height of the solder wave crest and the PCB. It transmits the real-time detection data of the solder wave peak height to the control computer through the real-time detection of the solder wave peak height sensor. After the computer processes the collected data and compares it with the set value, the Vectra's software system (supporting software) that controls the computer can calculate the deviation from the set value, and then automatically adjusts it based on the size and direction of the deviation. The rotation speed of the solder pump in the solder tank is used to correct the deviation and achieve the purpose of stabilizing the wave peak.

 

 

 

Vectra's software controls the average height of the wave peaks and troughs. It continuously collects data from the sensors, arranges and analyzes the data, and the average value of the data series is used to control the solder pump motor. If there are only peak or trough readings, Vectra's software cannot correctly control the peak height.

 

 

 

When the situation is abnormal, the input data column will stop new data input and the original data will be deleted, so that the data in the data column will always remain up-to-date. Of course, the shorter the data column, the faster the response; and the longer the data column, the more precise the control. For better control, faster response times are better, so shorter data columns are better. Through experiments, it was found that when the column length is set to 100 points, if there are 10 continuous anomalies, the collected data column length can be reduced to about 15 points to help correct more anomalies faster, such as just Boot time.

 

 

 

Vectra's software can control the wave soldering machine to stay in pause mode (that is, the wave is turned off for a short time), and resources will be automatically saved when no board is loaded. In order to start quickly and obtain suitable solder wave peak height, the pump speed before the last wave peak is saved periodically. When the PCB reaches a certain height with the wave crest (selected by the user), the pump will return to the previously saved speed; when the wave becomes stable (approximately 4s), the software begins to collect data again.

 

 

 

Through wave height mode control, a special sensor is used to measure the wave height and feed it back to the software to keep the wave height constant. The set point is the actual distance from the center line of the PCB. Adjust the set point up and down to keep the wave height higher or lower on the PCB. The actual value reflects the size of the wave height.

 

 

 

In order to reach the set point as quickly as possible, the following rules should be followed:

 

① Set the machine parameters according to the predetermined requirements, especially the foot spacing;

 

② Turn off wave height control;

 

③ Turn on the main wave and adjust the set point to the optimal value;

 

④ Save the set point and turn on the wave height control function.

 

The wave height control should use the set point of the main wave as the reference point. When the situation changes, the software will significantly adjust the motor speed to keep the wave height stable at the set point.

 

2) Single-phase AC electromagnetic pump-type solder wave peak height closed-loop control

 

The following introduces the application of conductive fluid magnetic flow stabilization technology, taking the pump groove action area of a single-phase liquid metal induction electromagnetic pump as an example, as shown in the figure below.

 

 

 

In the pump ditch area, under normal circumstances, due to the combined effect of the cohesion and adhesion of the fluid, the velocity distribution of the fluid when flowing through the pipeline is as shown in the figure below. The flow velocity is maximum along the center of the pipeline, and the velocity is zero close to the pipe wall. The uniformity of speed is very poor.

 

 

 

When a magnetic field is added to the rectangular flow tube, the situation changes significantly. Since the wire cutting the moving magnetic field lines is subject to the damping effect of the magnetic field, and the greater the speed, the greater the magnetic field damping force. The smaller the speed, the smaller the damping force. Therefore, the flow velocity distribution in the flow tube becomes very uniform, as shown in the figure below. Show.

 

 

Flow velocity distribution in flow tube under the influence of magnetic field

 

 

 

Due to the use of conductive fluid magnetic current stabilization technology, it has a relatively complete adaptive (self-learning) control capability against the impact of grid voltage fluctuations on the peak height stability. Its adaptive adjustment process is described below.

 

(1) Parameter setting

 

● According to process requirements, the peak height required to set the reference state is H0±10%;

 

● The corresponding pump excitation voltage is U0 (such as 220V);

 

● The magnetic flux is Φ0, the thrust is F0, and the magnetic damping force is f0;

 

● The fluid velocity is V0.

 

(2) Automatic stabilization process of excitation voltage (E) and wave speed (V) when the grid voltage fluctuates (U0±ΔU)

 

① When U0→U0+ΔU (grid voltage increases)

 

● The changing trend of parameters is E→U0+ΔU; Φ→Φ0+ΔΦ; F→F0+ΔF; V→V0+ΔVF.

 

● The action trend of induced electromotive force: As V and Φ increase, more magnetic lines of force are cut by the fluid per unit time. The direction of induced electromotive force is opposite to the direction of the grid voltage, and is -Δu, so there is

 

E→U0+ΔU-Δu; Φ→Φ0+ΔΦ-Δφ; F→F0+ΔF-Δf; V→V0+ΔVF-Δv

 

∵ |ΔU|≈|Δu|; |ΔΦ|≈|Δφ|; |ΔF|≈|Δf|; |ΔVF|≈|Δv|

 

∴ E→U0; Φ→Φ0; F→F0; V→V0

 

In this way, it is possible to automatically offset the impact on the stability of the wave peak height when the power grid voltage fluctuates upward, and achieve the purpose of automatically stabilizing the wave peak, as shown in the figure below.

 

 

 

The stabilizing effect of magnetic damping on the flow velocity in the flow tube (1)

 

 

 

② When U0→U0-ΔU (grid voltage drops)

 

● The changing trend of parameters is E→U0-ΔU; Φ→Φ0-ΔΦ; F→F0→ΔF; V→V0-ΔVF

 

● The action trend of the induced electromotive force: due to the decrease of V and Φ, the direction of the induced electromotive force is the same as the direction of the grid voltage, and is +Δu, so there is

 

E→U0-ΔU+Δu; Φ→Φ0-ΔΦ+ΔΦ; F→F0-ΔF+Δf; V→V0-ΔV+Δv

 

∵|ΔU|≈|Δu|; |ΔΦ|≈|Δφ|; |ΔF|≈|Δf|; |ΔV|≈|Δv|

 

∴ E→U0; Φ→Φ0; F→F0; V→V0.

 

In this way, the impact on the wave peak height caused by the downward fluctuation of the grid voltage can be automatically offset, and the purpose of automatically stabilizing the wave peak can be achieved, as shown in the figure below.

 

 

 

The stabilizing effect of magnetic damping on the flow velocity in the flow tube (2)

 

 

 

In the single-phase electromagnetic pump peak generator, the use of conductive fluid magnetic flow stabilization technology is my country's original solder peak flow stabilization technology. It does not require special structural design. It completely uses thrust magnetism to serve as both a heating magnetic field and a steady flow magnetic field. It is a solder wave peak stabilization technology with adaptive control capabilities. Compared with the actual flow stabilization effect of similar foreign technologies, as shown below shown.

 

 

 

 

 

 

 

    9. Closed-loop control of preheating temperature

 

Closed-loop control of preheating temperature is an effective means and prerequisite for realizing the optimization of preheating process parameters and the replicability of application effects.

 

    10. Nitrogen shielded wave soldering

 

Compared with Sn-37Pb, lead-free solder produces more oxides during welding and has poor wettability, especially during wave soldering.

 

 

 

In wave soldering, no matter what kind of lead-free alloy it is, if it is welded in N2 protection, the oxidation phenomenon of the solder will be significantly suppressed, and the amount of oxidized slag formed can be reduced by about 20 times compared with that in the air. The maximum wetting force and zero-crossing time are both better than in air. When welding is performed under N2 protection, the welding temperature can be lowered by about 15°C than in air.

 

 

 

The ideal situation is for a wave soldering equipment to have the ability to operate in air or N2. For cost reasons, N2 gas protection may not be used for general products; however, for complex designs such as high-density assembly, N2 gas protection should be used in a timely manner depending on the situation.

 

 

 

3. Equipment technology in the post-wave soldering era

 

    1. Raising the question

 

For high-density PCBA components that use a large number of SMC/SMD, the welding of a small number of special-shaped components (such as connectors, transformers, relays, electrolytic capacitors, etc.) is usually done by equipment and processing systems other than SMT in conjunction with wave soldering. Completed by the production line. High energy consumption, large amounts of flux, solder and N2 consumption make the wave soldering process very uneconomical, so complex solder masks have to be used to prevent devices on the PCB soldering surface from coming into contact with flux and solder. . These solder mask plates affect the uniform preheating of the assembled circuit board and increase contamination and flux residue on the assembled circuit board. In addition, its disordered solder flow also leads to an increase in welding defects.

 

 

 

Using solder mask to solve high-density mixed installation PCBA is a last resort and expedient. A high-power solder tank with a loading capacity of 500kg and a consumption of tens of kilowatts and a flux spray system with a large consumption are used to solder perforated solder joints that account for a few percent of the total number of PCBA solder joints. Resources (including auxiliary materials and electric energy ), the utilization rate is less than a few percent, which is really a huge waste.

 

    2. Equipment technology in the post-wave soldering era

 

To solve the welding problem of a small number of perforated components (such as connectors, etc.) on PCBA components that use a large number of SMC/SMD, and avoid the thermal damage and solder joint reliability problems caused by some existing welding methods, in the later wave Alternative technologies in the welding era include the following forms.

 

1) Point wave selection welding equipment system

 

   There are currently about 4 models of point wave selection welding equipment systems in the world, among which German ERSA is better, as shown in the figure below. However, this type of equipment has problems such as low production capacity, inability to be directly connected to high-efficiency SMT production lines, unsuitable for mass production, high cost of use, and high price, so its application is very limited.

 

picture

 

2) Local gap wave soldering system

 

(1) European model

 

① Pure local gap type. The German SEHO company has launched a pure local gap wave soldering system product on the market. The block diagram of the pure local gap type and the structural composition of the welding station are shown in the figure below.

 

 

② Local gap + click compound type. The block diagram of local gap + click selection and the structure of the welding station nozzle are as shown in the figure below. Companies such as German SEHO and ERSA have launched products of this model.

 

picture

 

(2) Japanese model

 

The device uses a piston drive controlled by a servo mechanism to generate local solder wave peaks. It is said that the state of the wave peaks can be finely controlled in this way.

 

(3) Advantages and disadvantages of local gap wave soldering system

 

① Advantages: ● High efficiency; ● Can be run in line with SMT production line.

 

② Disadvantages: ● It requires a large number of nozzle templates and has poor flexibility; ● It is too specific and lacks versatility, so it is not easy to market.

 

3) High-efficiency programmable multi-mode parallel wave selection welding system

 

The problems with existing welding methods include the following two points:

 

● The local selective welding system has insufficient versatility and poor flexibility;

 

● Point selective welding system has low productivity and high usage cost.

 

In view of the thermal damage and solder joint reliability problems caused by the above welding methods, we should implement energy conservation and emission reduction, reduce repair rate, reduce product production costs, and develop a new alternative equipment for the post-wave soldering era to meet the needs of modern electronic equipment. The interconnection needs in high-density mixed installation situations is what the industry is pursuing.

 

 

 

"High-efficiency programmable multi-mode parallel wave selective welding system" is a new design concept proposed to effectively overcome the shortcomings and deficiencies of point selective welding and local gap selective welding technologies.

 

The outstanding advantages of this method are: ● High efficiency, comparable to the wave soldering process; ● Can be connected to the SMT production line for operation. ● Low cost of use, good performance-price ratio, and large space for promotion and application.