Semi-automatic Surface Mount Technology Instruction For PCB Board

Surface-mount technology (SMT) is a method to mount components directly onto the surface of printed circuit boards. An electronic device so made is called a surface-mount device (SMD). In the industry it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of solder balls (BGAs), or terminations on the body of the component. More and more engineers would like to chose SMD parts instead of DIP parts, but SMT equipment is so big and expensive. Wonderful PCB suggest a much better method for engineers who want to SMD himself but don’t want to pay too much for SMT machine.  We called it  semi-automatically Surface mount.  Wonderful PCB suggest customer to do as following processes, 

1. Buy solder paste.  Solder paste 500g imported one around USD 100, Solder paste 500g made in China around USD 80. Two kinds of solder paste, Tin lead and leadfree. Leadfree is around USD 20 per 500g higher than Tin lead. The solder paste should be kept in 0-10°C condition.
2. Make the stencil according to the PCB Gerber( pads needed hollow out). Serval kinds of size of stencil. Normal size is 370mm*470mm,420mm*520mm,470mm*570mm. Nomral thickness of stencil is 0.13mm. it have to be with fiducial marks half etched or hollow out. Fiducial marks size usually is dia. 1.5mm.
3. Fix the stencil on the machine as pic 1 shows.
4. Fix the PCB on the machine. Usually PCB board should have borders at least 5mm at two sides with tooling holes . Then PCB could be fix steadily to the machine. Tooling holes size usually is 3.2mm.
5. Put stencil on the PCB 
6. Print solder paste on the stencil, then when you lift up the stencil, PCB are with solder paste.
7. Put the components on the solder paste on PCB.
8. Put the PCB with solder paste and components to reflow Oven. Reflow Oven temperature is around 225-240℃ for tin lead solder paste and 250℃ for lead free solder paste. the solder paste will melt and assemble the components.