Requirements of SMT technology for components inst

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The requirements of surface mount SMT technology for components

the emergence of surface mount technology promotes electronics and ensures that the speed accuracy is within ± 1% of the indicated value. The equipment is moving towards miniaturization, lightness, high reliability, multi-function and other directions, so as to meet the needs of military and civil electronic equipment. Due to the difference between the surface mounting and the original component assembly technology, the following requirements are put forward for the components and related materials used for surface mounting:

(1) miniaturization

on the premise of ensuring the electrical parameters, the volume of components and parts is reduced and the weight is reduced, which is generally made into pieces to meet the needs of surface mounting

(2) heat resistance

specific welding process is adopted for surface installation. During the welding process, the components installed on the printed circuit board or substrate need to enter the high-temperature welding area, which generally needs to withstand the thermal shock between 210 ℃ -260 ℃ for about 10 seconds, and some components work under the conditions of high heat flux and poor heat dissipation conditions. Therefore, the components should have heat resistance, so that they can withstand thermal shock and maintain their original electrical parameters when working at the allowable working temperature

(3) the experimental force weldability of elastic yellow can be measured accurately or under specific length

electronic equipment using surface mounting technology generally adopts high assembly density structure, and components are made of leadless or short leads. Poor weldability will lead to the hidden danger of false soldering and reduce the working reliability of electronic equipment. In order to ensure the stable and reliable operation of electronic equipment, we must pay attention to the weldability of welding areas and components, and carefully check the quality of welding joints

(4) coefficient of thermal expansion

components are welded on the printed board or substrate. If the coefficient of thermal expansion of the two materials is different, after welding and cooling, shear stress will be formed in the solder joint, and tensile and compressive stress will be produced in the components and substrate. These stresses will cause damage and tear of the solder joint and reduce the working reliability. Therefore, in the design, the thermal expansion system should be selected according to different working requirements, so VRB batteries can either charge materials matching the number of charges, or adopt compensation structure to reduce and eliminate thermal stress

(5) high accuracy

at present, the wiring spacing has reached 0 1mm, and it is progressing towards less than 0.1mm. During assembly, the components and parts are pasted on the printed board by an automatic mounter. If the processing error is large, so that the components cannot be accurately pasted on the original set position, there will be open circuit or faulty soldering, and the circuit will not work normally. Therefore, the machining accuracy must be guaranteed

(6) tightness

according to the current process, cleaning is required after welding. In order to ensure the performance of components, the cleaning fluid should not enter the components. During the welding process, components (such as electrolytic capacitors) are heated, the internal medium expands and the internal pressure increases, and the medium will flow out and become invalid. Therefore, it is necessary to ensure and improve the sealing of component packaging

(7) small deformation and high stability

both printed boards and components need to enter the high-temperature area during welding. During the processing of ceramic substrates, baking and high-temperature alkane bonding are required. If the stability of materials is poor, deformation will occur after processing, and the printed board will warp, resulting in a gap between the welding feet of components and the bonding pads on the printed board. Excessive gap will cause false soldering. Experiments show that the warpage before welding is greater than 0.3%, which is prone to false soldering. After high-temperature welding, if the printed board is deformed and warped, the stress of the solder joint will be increased, and finally the solder joint will tear, resulting in open circuit

(8) standardization

automatic mounter is used for surface mounting to paste components and parts as one of the official partners of the project. On the printed board, if there is no unified standard for components and parts, it will bring unnecessary difficulties to circuit design and automatic mounting. Therefore, while studying the components for surface mounting, it is necessary to formulate general standards. (end)

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