In the traditional electronic cable assembly process, the wave soldering technology is generally used for the soldering of printed board components with PTH.

However, wave soldering has many shortcomings:

① High-density and fine-pitch patch components cannot be distributed on the surface.

(2) bridging, welding leakage is more.

(3) It needs to be sprayed with flux, and the printed board is warped and deformed by large thermal impact.

As the current circuit assembly density is getting higher and higher, there will inevitably be high-density and fine-pitch patch components distributed on the soldering surface. The traditional wave soldering process can't do anything about it. Generally, only the patch components on the soldering surface can be reflowed separately, and then the remaining plug-in solder joints can be repaired manually, but there is a problem of poor consistency of solder joints.

The following five new mixed welding processes of Kable-X

1 Selective Welding

In selective welding, only some specific areas are in contact with solder waves. Because PCB itself is a bad heat conduction medium, it will not heat and melt the solder joints of adjacent components and PCB areas during welding.

Before soldering, flux must also be applied in advance, which is only applied to the lower part of PCB to be soldered, but selective soldering is not suitable for soldering patch components.

2 Immersion Welding Process

Using immersion selective welding process, 0.7 mm ~ 10 mm solder joints can be welded. The welding process of short pins and small size pads is more stable, and the possibility of bridging is small. The distance between adjacent solder joint edges, devices and welding nozzles should be greater than 5 mm.

Select the immersion welding process, and the following parameters can be set:

① Solder temperature is 275℃ ~ 300℃

(2) the immersion speed is 20 mm/s ~ 25 mm/s.

③ Immersion time is 1s ~ 3s.

④ The speed after soaking is 2mm/s.

⑤ The speed of shock pump is determined by the number of welding nozzles.

3 Through-Hole Reflow Soldering

Through-hole reflow soldering technology (THR) is to use reflow soldering technology to assemble through-hole components and special-shaped components.

Because products pay more and more attention to miniaturization, increasing functions and increasing component density, many single-sided and double-sided panels are mainly surface mount components.

However, due to inherent strength, reliability and applicability, in some cases, through-hole devices are still superior to SMC, especially connectors at the edge of PCB.

The disadvantage of using through-hole devices on circuit boards with surface-mounted components is that the cost of a single solder joint is very high. For this kind of assembly, the key is to provide synchronous reflow soldering for through-holes and surface-mounted components in a single comprehensive process.

Compared with the general surface mount process, the amount of solder paste used in the through-hole reflow process is more than that of the general SMT, which is about 30 times. At present, through-hole reflow process mainly adopts two solder paste coating technologies, including solder paste printing and automatic solder paste dispensing.

(1) Solder Paste Printing

Screen printing is the first choice to deposit solder paste on PCB. The thickness of screen is the key factor, which will affect the amount of solder paste missing from PCB. A stepped screen can be used, in which the thicker area is specially designed for through-hole devices. This steel mesh design can meet the requirements of different solder paste content.

⑵ Automatic Soldering Paste.

Automatic solder paste dispensing successfully deposits the correct volume of solder paste for through holes and special-shaped components, which provides flexibility and ability for depositing a large amount of solder paste that screen printing may not be able to achieve. It is recommended to use a nozzle with a slightly larger diameter than the exposed plated through hole (PTH) when dispensing solder paste. In this way, when soldering paste, the solder paste is forced to cling to the hole wall of PTH, and the material is slightly extruded from the bottom of PTH, and then the component is inserted from the opposite direction of soldering paste. If a nozzle with a smaller diameter than PTH is used, solder paste will be discharged from the hole and cause serious solder paste loss.

Through-hole reflow soldering can replace wave soldering in many aspects to realize the soldering of plug-in components, especially the soldering of plug-in solder joints with high-density patch components (or SMD with fine spacing) on the processing welding surface, which greatly improves the welding quality, which is enough to make up for the lack of expensive equipment.

The appearance of through-hole reflow soldering is of great help to enrich welding methods, improve the assembly density of circuit boards, improve welding quality and reduce technological process.

4. Wave Soldering Process Using Shielding Mold

Because the traditional wave soldering technology can't cope with the soldering of fine pitch and high density patch components on the soldering surface, a new method arises at the historic moment: using shielding die to shield the patch components to realize wave soldering of lead inserted on the soldering surface.

⑴ Advantages of Wave Welding Technology with Shielded Mould

(1) wave soldering production of double-sided mixed PCB can be realized, which can greatly improve the production efficiency of double-sided mixed PCB and avoid the problem of poor quality consistency in manual welding.

(2) reduce the preparation time for pasting solder resist, improve production efficiency and reduce production cost.

③ The output is equivalent to that of traditional wave soldering.

⑵ shielding mold material

① The mold must be antistatic, and the common materials are: aluminum alloy, synthetic stone and fiberboard. When using synthetic stone, it is recommended not to use black synthetic stone in order to avoid non-induction of wave soldering sensor.

(2) that thickness of the base material of the mould is made, and the base material with the thickness of 5-8 mm is selecte to make the mould according to the thickness of the back component of the machine disc.

⑶ Requirements of Die Process Size

① overall dimensions of the mold: the length and width of the mold are respectively equal to the length and width of the PCB plus the width of the carrier side of 60mm, and the width of the mold must be ≦350mm. When the width of PCB is less than 140mm, it can be considered to place two PCBs in one mold for welding.

(2) The technological edge is 8mm away from the edge, and 10mm wide and 10mm high bakelite strips are installed at the other two sides close to the edge to increase the strength of the mold and reduce the deformation of the mold.

(3) each reinforcing bar must be fixed with screws, and the space between screws is below 150 mm.

(4) After the mold is made, it is necessary to install snap fasteners (fixing PCB on the mold) around and within 100mm distance, and pay attention to the following points:

Rotate once without touching the parts.

Does not affect DIP plug-ins

The PCB can be firmly fixed to the mold.

(PCB punching die)

⑤ Four corners of the mold should be chamfered with R5.

⑥ When PCBA on the mould passes through the tin furnace, some parts will float due to the impact of tin wave, so some parts that are easy to float will be solved by pressing parts.

At present, the main methods are:

Metal iron block pressing piece

A pressing piece is installed on the die.

Fixture for manufacture anti-floating high-pressure parts

5 Automatic Soldering Machine Technology

(1) Because the traditional wave soldering technology can't cope with the welding of double-sided patches, high-density patch components and components that can't withstand high temperature, a new method arises at the historic moment: using automatic soldering machine to realize the welding of welding surface plug-ins.

(2) Advantages of using automatic soldering machine technology:

① Small investment and quick results.

(2) Realizing automatic welding production can improve the consistency of solder joints, save manpower, improve production efficiency and reduce manufacturing cost, and avoid the problem of poor consistency of solder joints in manual welding.

summary

Which welding technology to choose depends on the product characteristics:

(1) If the products are small in batch and varied, the selective wave soldering technology can be considered, and there is no need to make special molds, but the equipment investment is large.

⑵ If the product category is single and the batch is large, and it wants to be compatible with the traditional wave soldering technology, the wave soldering technology using shielded mold can be considered, but special mold needs to be invested. These two welding technologies are well controlled, so they are widely used in electronic assembly production at present.

⑶ Through-hole reflow soldering is more difficult to control, and its application is less than the former, but it is of great help to improve welding quality, enrich welding methods and reduce technological process, and it is also a very promising welding method.

⑷ Automatic soldering machine is easy to master, and it is a new welding technology that has developed rapidly in recent years. It has the characteristics of flexible application, low investment and low maintenance cost, and it is also a very promising welding technology.

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