The requirements for SMT stencil design -1
Assembled in SMT technology , the printing industry is the first link is a very important part . The quality of the printing quality will directly affect the SMT soldering through -out rate , in the actual production process, we found that 60% -70 % of the welding defects and quality of the print . Therefore, it is necessary to carry out all aspects of printing technology research . Affecting all aspects of the printing process , stencil design plays an important role .
General technical requirements :
1 , the net box :frame size according to the requirement of printing to DEK265 and MPM UP 3000 model , for example, frame size 2929 , use of aluminum , the frame sections 1.5 and 1.5 specifications .
2 Stretching : The way red plastic + aluminum tape , aluminum frame and Adhesives Division , to even scratch the paint layer of protection . To ensure the network board has enough tension and good flatness , the proposed network box from the inside of stainless steel to retain 25mm-50mm.
3 , reference point : According to information provided by the PCB size and shape of openings 1:1 mode , and a negative moment in the printing transflective . In the corresponding coordinates , block PCB open at least two reference points .
4, opening requirements: 1.41 . Location and size of openings to ensure high accuracy , open manner in strict accordance with the provisions of the opening . 1.42 . Independent opening size can not be too large , the width is not greater than 2mm, pad size greater than 2mm in the middle of the bridge need to 0.4mm frame , so as not to affect the net plate strength . 1.43 . Opening area must be centered .
5 characters : To facilitate the production , the proposed lower left or lower right corner of the net plate engraved the following characters : Model; T; Date; network board production company name.
6, stencil thickness : To ensure the quality of solder paste printing and welding , stencil evenly smooth surface , uniform thickness, net thickness refer to the table above , net plate thickness to meet the most fine pitch QFP BGA as the premise. If there 0.5mmQFP PCB and CHIP 0402 components, net thickness 0.12mm; such as PCB and CHIP 0603 there 0.5mmQFP more components, net thickness 0.15mm;