PCB Assembly manufacturer
Printed tin plate open net shape and size requirements:
1 , General principles: based on IPC-7525 Stencil Design Guidelines requirements, in order to ensure smooth paste can be released from the stencil to the PCB pad openings on the board in the net opening , the main dependent on three factors: 1 ) area ratio / area ratio of width to depth ratio > 0.66 2 ), mesh smooth hole wall . Especially for spacing less than 0.5mm of QFP and CSP, the production process requirements for electricity suppliers polished . 3 ) to the printing surface as above , under the mesh openings should be less than the opening width of 0.01mm or 0.02mm, which open into the inverted cone , to facilitate the release of solder paste is not effective , while reducing the number of stencil cleaning . Typically , SMT components on its web board pad opening size and shape and line , by way of opening 1:1 . Special circumstances, special SMT components, the stencil opening size and shape of a specific requirement.
2 Special SMT components stencil opening :
2.1CHIP components: more than 0603 CHIP components , in order to effectively prevent the formation of tin beads .
2.2SOT89 components: As large pad and the component pad spacing small , prone to quality problems , such as welding tin beads .
2.3 SOT252 components: a pad because SOT252 great , easy to produce solder balling , and the tension is caused by displacement of reflow .
2.4IC: A. The standard pad design , PITCH "= 0.65mm the IC, the opening width of 90% of pad width , length unchanged . B. The standard pad design , PITCH "= 005mm of IC, because of its PITCH small , prone to bridging , steel CAPE way length of the same mouth , open width 0.5PITCH, opening width of 0.25mm.
2.5 Other cases : a pad is too large, usually one side more than 4mm, the other side is not less than 2.5mm , in order to prevent the formation of tin beads as well as the role of tension caused by the displacement of stencil openings proposed grid segmentation approach , Grid line width of 0.5mm, the grid size of 2mm, pad size can be shared equally . India rubber stencil opening shape and size requirements: PCB assembly with glue on the simple process , preferred dispensing , CHIP, MELF, SOT components through plastic stencil printing , IC is as far as possible to avoid dispensing stencil Squeegee . Here, only gives CHIP, MELF, SOT India rubber stencil opening size recommendations , open shape . 1 , mesh panels on the corner to open two pairs of angular positioning holes , select FIDUCIAL MARK point hole . 2 , openings are elongated . Test Method 1 ) by visual inspection openings centered Stretching formation . 2 ) physical check through the stencil openings PCB correctness . 3 ) test with high power microscope with a scale length and width of the stencil openings and the pore wall and the steel surface smoothness . 4 ) steel sheet thickness after solder paste printing by detecting the thickness to verify that the results show . Conclusion stencil design requirements after a period of trial , the printing quality was well controlled , the performance of PPM in SMT solder quality defects around the 1300ppm down to around 130ppm . Because of modern electronic components package directions , on the steel mesh design is also a higher demand. We need to focus future research topics .