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How to install PCB board components in SMT chip processing

时间:2017/05/07  点击量:14
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For the PCB copy board, the quality of the components have three elements: the correct components, accurate location, pressure (patch height) appropriate.

1 components are correct - requires the assembly of the number of components of the type, model, nominal value and cabinet polarity, such as the characteristics of the product to meet the assembly drawings and detailed list requirements, can not be affixed to the wrong location.

2 accurate position - the end of the component or the pin and the pad to be as far as possible alignment, center. Component placement position to meet the process requirements. Because the role of the two ends of Chip element positioning effect is relatively large, Mount element length direction of the two ends as long as lap to the corresponding pads on the width direction 1/2 lap on the pad, reflow soldering will be able to self localization, but if one is not to end lap welding disk, reflow soldering will be generated when the shift or suspension bridge: for SOP, SOJ, QFP, PLCC and other components of the self localization effect is relatively small, Mount offset is not through the reflow correction. Must therefore mount that pin width 3 / 4 in the pads, pins of the toe and heel portions should also be on the pad. If the placement position exceeds the allowable deviation range, must be set right before entering the artificial reflow soldering welding. Otherwise reflow welding must be repaired, will cause work hours, material waste, and even affect the reliability of the product. In the production process, it is found that the mounting position should be corrected in time. Manual placement requires accurate placement, the pin and the pad is aligned, centered, do not stick to the right, in the solder paste on the right, so as to avoid the paste pattern adhesion, resulting in bridging.

3 pressure (patch height) - patch pressure (height) should be appropriate, the welding end of the component or pin is not less than 1 / 2 thickness to dip into the solder paste. For the patch elements like paste extrusion quantity (length) should be less than 0.2mm, for the narrow spacing of the patch components of solder paste extrusion amount (length) should be less than 0.1mm. The pressure of the chip is too small, the solder end or the pin of the component is floating on the surface of the solder paste, and the solder paste can not adhere to the components. In addition, due to the height of the Z axis is too high, when the chip components from the height of the drop, will cause the placement of the patch offset. Patch pressure is too large, excessive amount of solder paste, solder paste is easy to cause adhesion, reflow soldering prone to bridging, serious damage to components.


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