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PCB Reverse Welding Technology stencil, Sn paste, Components selection

Stencil
(1) should be used cast steel plate
Commonly used in the printing of solder paste steel plate made of stainless steel by laser, but in the welding for 0201 components, the laser made of steel plate wall finish is not high, should be made by electroforming template, it can Get excellent solder paste printing effect.
(2) to correct the steel window size
PCB Reverse graphics actual size is not equal to the PCB graphic design size, it should be based on the actual size of the PCB graphics to determine the size of the steel window, and do PCB-related graphics size records, not free to replace thePCB Reverse manufacturer, metal mesh plate size accuracy Control in lOym (± 0.01% accuracy).
Paste
Paste is a very important process in the welding process of auxiliary materials, solder paste in the 0201 components in the welding more important role, the choice of solder paste can refer to the following requirements:
(1) solder paste printing
Micro-graphic printing is to ensure that 0201 component patch one of the key factors, usually combined with AOI detector, control solder paste printing accuracy within ± lOpm, the printing accuracy of the stability of continuous production is guaranteed.
(2) a comprehensive inspection of the physical properties of solder paste
Paste physical properties include: solder paste flow characteristics (viscosity), adhesion, flux content, slump, tin powder particle size and distribution and other indicators. Often, the solder paste drying time is short, will appear in the printed circuit process due to downtime and bring the printing graphics quality degradation or can not use the phenomenon; solder paste adhesion weak, dry and fast after printing, in the placement of 0201 components, There will be flying film phenomenon; solder paste easy to collapse will appear after the phenomenon of reflow after welding, it should be emphasized that the high temperature solder paste does not slump, the test conditions in the 150 0C oven put 60s, solder paste should not appear collapse drop.
(3) PCB Reverse solder paste electrical performance test
In the use of no-clean solder paste, the solder paste electrical indicators should be comprehensive, qualified, including copper corrosion, insulation (high temperature and humidity), residues in the ionic (permanent solution after the resistivity), otherwise it will be direct Affect the performance of mobile phones.
The dimensional accuracy and packaging of components
0201 components are ultra-small components, components should have a good appearance size, the surface should be smooth to ensure that the placement machine with the precision of the nozzle, the components can be precisely after the patch on the pad, Component size error or placement machine accuracy is not enough will cause flaw defects. 0201 components of the electrode size is also an important indicator, the electrode size is different, the occurrence of different ball phenomenon. In addition, most of the 0201 components using disc-like packaging, so the required size of the cavity to be stable, no burr or deformation, dimensional stability, which is to ensure that the components after the patch can accurately fall on the conditions of the pad One, it should be fixed-point selection of components manufacturers to ensure that the size of the consistency of components.
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