Circuit board welding is an important part of electronic technology. Correct welding joint design and good machining technology are the key factors to obtain reliable welding. Xiaobian for you to finish the circuit board welding technology paper, I hope you like.
Circuit board welding technology paper I
Some understandings on the welding and wiring of printed circuit board
Abstract: PCB welding is an important part of electronic technology. Correct welding joint design and good machining technology are the key factors to obtain reliable welding. “Reliable” means that the solder joint not only has all the properties required when the product is first produced, but also works correctly throughout the life of the electronic product.
Key words: circuit board welding wiring principle
Welding is one of the important links in the manufacturing of electronic products, if there is no corresponding process quality assurance, any well-designed electronic products are difficult to meet the design requirements. The function of electronic products depends on the correct interconnection of electronic components, and the interconnection of these components is mostly based on the circuit board welding. The circuit board welding has been playing an important role in the assembly of electronic products. Even though there are many connection technologies available today, circuit board welding remains the dominant technology.
Although the physical-chemical principles of all welding processes are the same, the welding of electronic circuits has its own characteristics, namely high reliability and miniaturization, which is consistent with the characteristics of electronic products. The welding quality of circuit board is affected by many factors. For example, the type of the substrate material and its surface layer and coating type and thickness, processing technology and method, the surface state before welding, flux composition, welding method, welding temperature and time, the gap size of the substrate to be welded, flux type and performance, welding tools, etc. Not only the oxides on the surface of the lead wires of the components being welded and the intermetallic compounds in the internal structure of the lead wires are the important factors affecting the solderability of the lead wires, but also the oxides on the surface of the printed board are the main factors affecting the solderability of the pads.
The quality of the solder depends mainly on the ability of the solder to wetting the surface of the solder, that is, the wetting and solderability of the two metal materials. If the weldability of the weldment is poor, it is impossible to solder a qualified joint. Weldability refers to the ability of the weldment and solder to form a good combination under the action of appropriate temperature and flux. Not all materials can be connected by tin welding, only some metals have good weldability, generally copper and its alloy, gold, silver, zinc, nickel and so on have good weldability, and aluminum, stainless steel, cast iron and so on are very poor weldability. Special fluxes and methods are generally required to solder.
In order to achieve a good combination of solder and weldment, the weldment surface must be kept clean. Even for weldables with good weldability, if there is oxide layer, dust and grease on the weldments surface, it must be cleaned up before welding, otherwise the formation of alloy layer around the weldments will be affected, thus the welding quality cannot be guaranteed. Manual welding is a traditional welding method. Although the production of bulk electronic products is less manual welding, it is inevitable to use manual welding in the maintenance and debugging of electronic products. The quality of welding also directly affects the maintenance effect. Manual welding is a practical skill, after understanding the general method, to practice more; More practice, can have better welding quality. The circuit board welding wiring should pay attention to several principles I summarized as follows.
1. The edge lines of the input end and the output end should be avoided to be parallel to each other to avoid reflection interference. If necessary, ground wire should be added for isolation. The wiring of two adjacent layers should be perpendicular to each other. Parallelism is easy to produce parasitic coupling.
2. Common ground processing of circuit and analog circuit. Many PCBs are no longer single-function circuits (digital or analog), but consist of a mixture of digital and analog circuits. Therefore, it is necessary to consider the interference between them when wiring, especially the noise interference on the ground wire. The sensitivity of the high frequency digital circuits, analog circuits, the signal wire, high-frequency signal lines as far as possible away from the sensitive analog devices, for the ground, the PCB to the outside world is only one node, so must be within the PCB processing, mold has problem, and inside the plate to digital and analog is actually are divided between them, only Is in the PCB and the outside connection interface (such as plug, etc.). There is a short connection between the digital and the analog. Note that there is only one connection point. There are also on the PCB, this is determined by the system design.
3. The bending of the wire is generally taken as a circular arc, while the right Angle or included Angle will affect the electrical performance in the high-frequency circuit. If a right Angle must be taken, two 135° angles are generally used to replace the right Angle.
4. Handling of connecting legs in large area conductors. In a large area of grounding (electricity), the legs of commonly used components are connected with it. The treatment of the connecting legs needs comprehensive consideration. In terms of electrical performance, it is better for the solder pad of the component legs to be fully connected with the copper surface, but there are some bad hidden dangers for the welding assembly of components, such as: (1) Welding requires a high-power heater. ② easy to cause virtual solder joint. Therefore, taking into account the electrical performance and process needs, we make cross-shaped welding pads, which are called heatshield, commonly known as Thermal welding pads. In this way, the possibility of creating a virtual solder joint due to excessive heat dissipation of the section during welding is greatly reduced. The same is done for the grounding leg of the multilayer board.
The grounding wire should be thickened as far as possible. If the grounding wire is very thin, the grounding potential changes with the current, so that the anti-noise performance is reduced. Therefore, the grounding wire should be thickened so that it can pass three times the allowable current on the printed board. If possible, the grounding wire should be above 2-3mm.
6. Correct single and multi-point grounding. In the low-frequency circuit, the signal operating frequency is less than 1MHz, its wiring and the inductance between the devices have little influence, and the grounding circuit formed by the circulation has a greater influence on the interference, so a point grounding should be used. When the signal operating frequency is greater than 10MHz, the length of the ground wire should not exceed 1/20 of the wavelength if one point grounding is used, otherwise the multi-point grounding method should be used.
7. When the signal wire is distributed on the electrical (ground) layer and the multi-layer printed board is distributed, because there are not many wires left in the signal wire layer, adding more layers will cause waste and increase the workload of the production, and the cost will increase accordingly. To solve this contradiction, it is possible to consider wiring on the electrical (ground) layer. The power supply layer should be considered first and the formation should be considered second. It is best to preserve the integrity of the formation.
8. As far as possible, shorten the wiring between high-frequency components and try to reduce their distribution parameters and electromagnetic interference between each other. Vulnerable components should not be placed too close to each other, and input and output components should be kept as far apart as possible. There may be a high potential difference between some components or conductors, so the distance between them should be increased to avoid an accidental short circuit. Components with high voltage should be arranged as far as possible in a place that is not easy to touch when debugging.
9. Design rule check. Wiring design is completed, it is necessary to carefully check the wiring design by the designers is in line with the rules, rules at the same time also need to confirm whether accord with the demand of the PCB production process, general examination has the following several aspects: line to line, line with element bonding pad, the line and communicating pores, element bonding pad and communicating pores, through hole and the distance between the through hole is reasonable, whether to meet the production Please? Are the power cords and ground wires of appropriate width and tight coupling between the power and ground wires (low wave impedance)? Is there any place in the PCB where the ground wire can be widened? Are the best practices used for critical signal lines, i.e. minimum length, guard lines, and clear separation of input and output lines? Are there separate ground lines for analog and digital circuits? Will the graphics (such as icon, mark) added to PCB cause signal short circuit? Modify some undesirable lines. Is there any process line on PCB? Is the solder stopper consistent with the manufacturing process, is the solder stopper size appropriate, and is the character mark pressed on the device pad? So as not to affect the quality of Denso. Are frame edges of the power source formation in multilayer panels reduced? If the copper foil of the power supply layer is exposed, it is easy to cause a short circuit.
The purpose of this paper is to explain the process of PCB PCB design and some matters needing attention, to provide design specifications for designers, facilitate the designers to communicate and check each other.
 Gao Chuanxian. Electronic technology application basic project course.
 Han Guangxing, et al. Practical training on basic application skills of electronic technology.
Circuit board welding technology paper II
Research on the key technology of assembly unit of circuit board assembly and welding automatic production line
Abstract: This paper first describes the general situation of the circuit board assembly and welding automatic production line, comprehensive analysis of several more common production line transportation scheme, for the circuit board assembly and welding of the main characteristics of the analysis, the design of the suitable production line transportation scheme and the key technology in the process, Finally, the paper summarizes the related process of the circuit board assembly and welding automatic production line.
Key words: circuit board; Assembly welding; Automatic assembly; The key technology
1 the introduction
The circuit board assembly welding automatic production of many main technology and a part of the small parts of the automatic assembly has many similar characteristics, the results obtained can also be widely used in many other products of the automatic assembly. Moreover, the automatic assembly and welding production line is relatively soft and intelligent, so it has paved the way for the application of automatic assembly line in various fields, so that the production line has a great advantage compared with other similar technologies. Therefore, it is of great significance for manufacturing industry to study the technology of automatic production of key parts of assembly unit in circuit board assembly and welding, and it has certain practical application value.
A comprehensive description of the automatic production line during the circuit board assembly and welding
The circuit board assembly and welding automatic production line is a relatively perfect automatic assembly line, composed of a moderate number of small parts, high precision, faster production speed. It is mainly used for welding and assembly of base shell and high dielectric circuit board. The conveying process of the product of the production line plays a very important role in the overall efficiency. The structure, positioning mode, assembly precision and efficiency of the assembly line and many other operations are all determined by the quality of the conveying technology of the product of the production line.
2.1 Selection of conveying scheme in automatic production line during circuit board assembly and welding
Based on the summary analysis of the production needs of circuit board assembly and welding and the reference of some advanced experience at home and abroad, the following transportation schemes are analyzed and compared.
The first is the multi-station rotary scheme, this transport scheme is to take the rotating table as the main body, all kinds of assembly stations are fixed on the edge of the table respectively in a certain order, the bottom plate of the product is placed on the rotating table at the same time, after the table starts to rotate, the product is then allocated to each specific position. The process of this method is simple, the actual operation is easier, and because of the concentration of the station, the failure is easy to be eliminated, and the product can meet the requirements of high precision. But there are also some disadvantages, the device covers a large area, and “affect the whole body”, that is to say, as long as a station failure, it will lead to the whole process can not be carried out normally.
The second is the following pallet step-by-step transportation scheme. The operation method of this scheme is to fix the bottom plate on the pallet first, and then operate it after the pallet is all fixed in a specific position. The advantage of using the following tray step transportation scheme is that the positioning hole size of the following tray is basically the same, the accuracy is very high, and the operation is relatively soft, and it can put different kinds of products on an assembly line without the release device. However, as with the first mode of transport, once a problem occurs in one part, the whole unit can not carry out the normal work.
The third is the accompanying tray asynchronous transport scheme. The structure of the device is basically the same as that of the accompanying tray transport scheme, but the accompanying tray is continuously conveyed along the conveyor belt, so the device should be put. This solution can set buffer distance on the conveying line, so that if a station fails, the whole production line can not stop working, so that the technical personnel can remove the obstacles in time.
Direct synchronous transmission, the fourth is the product bottom positioning scheme for many times, can use this solution conveying mechanism to base shell directly to travel for, in this way, each station can directly positioning the base shell, the scheme combines the advantages of the first three solutions, so in general have chosen in the process of actual production adopts synchronous transport, multiple positioning solution.
2.2 Briefly analyze the process of automatic production line in circuit board assembly and welding
First in the shell welding paste, check no problem before positioning and base shell material on the circuit board, after the image measurement, after assembling the base shell with fixture, and around the seam and the hole place coated with rubber resistance welding, after curing, welding, final fixture is removed and the products are to clean .
In the base shell feeding, because the device is soft, the connection is not rigid, the basic can operate freely, suitable for various sizes of the base shell feeding work, the following introduces a can store different sizes of the base plate and can be freely adjusted feeding device. That is, the self-made transmission belt equipped with the material frame on both sides rotates in the opposite direction, and the base shell is sent from the feeding device to the production line below in a top-down order. And the position of the transmission belt can be adjusted appropriately according to the base shell of various sizes .
With the continuous progress of science and technology, circuit board plays an extremely important role in radar, aviation and other high-tech fields. The problem of product failure caused by poor contact of circuit board has been paid more and more attention. In order to improve this situation, the voids in the welding of high dielectric circuit board and base shell must not exceed 10%, especially the surrounding welds are not allowed to leak. Therefore, the operation of inspection of welding points should be increased after welding and printing .
The details of the related scheme in the circuit board assembly
There are many details that need to be paid attention to in the circuit board assembly station. The following is a brief analysis of the design scheme of the material mechanism on the circuit board to enable the base shell to accurately locate these two problems.
(I) Make the circuit board station to form an operating production line, place several groups of circuit boards on the accompanying tray, and the robot will use the image to distinguish the signal displayed on the circuit board and then assemble the circuit board into the base shell. In this process, a feeding device for recovering the empty tray should be set up . The whole device is shown in Figure 1:
Figure 1 circuit board stacking, feeding mechanism design scheme
(2) the use of conveyor belts to base shell to the circuit board assembly station, under the condition of the circuit board assembly accuracy is higher, the shell of the positioning accuracy of the corresponding also improve a lot, and because to simplify the work completes the assembly station, as far as possible to reduce the process cost, to the other design operating process, can make the base shell in the XY plane fully.
The above introduces several automatic production line transportation scheme, and through the comparison finally established the most appropriate overall transportation scheme, and then for the circuit board assembly welding automatic production line problems were analyzed and determined the process flow. China’s scientific and technological level continues to develop, in the efforts of all the staff, circuit board assembly and welding automatic production line will be more and more perfect.