The objective of the solder paste printing process is to consistently deposit the proper volume of solder paste in the right place. In the SMT manufacturing process there are two common material approaches to the fabrication of these stencils: plastic and metal stencils.
Plastic stencils are an economical alternative to metal stencils specifically designed for prototypes and low-volume runs of PCBs. If your design is relatively simple, has larger pitches (> 0.8mm) devices and relatively large (> 5mil) spaces and traces, then it is candidate for a plastic stencil. Also smaller print areas (< 6 x 6”) are a good candidate using plastic stencils.
While these stencils are very capable tools for these limited applications, they should be used with caution.
The other material used for the fabrication of the SMT stencil is metal. Metal stencils are most commonly made from stainless steel or stainless derivative alloys. These alloys can be cut with the laser with few induced problems. They have great side wall release characteristics and they are durable for most low and high volume printing applications. In addition metal stencils can be place into frameless stencils which are under tension of stencil frames which provide good rigidity. In addition these metal stencils work well in environments using todays’ SMT assembly materials such as lead free solders and fluxes and other stencil cleaning chemicals.