Describe about major SBT process

     The major substrate process primarily focuses on subtractive(tenting) and semi-additive(mSAP). You can see the graph showed that the top and bottom width of copper trace shape is different. In order to achieve better reliability criteria, mSAP has better performance than tenting, as its trace width is better and resist to trace to broken earlier.

    Subtractive manufacturing is started by attaching the photo-sensitive dry film to the surface(CCL), then cover by negative film, and then use UV-light to irradiate dry film through negative film. The pattern will be transferred to the dry film. The rest of the unpolymerized will be dissolved by using sodium carbonate solution. The uncovered copper will be etched by solution. Finally, the polymerized dry film is removed and then we get the circuit traces.

    Semi-additive(mSAP) was come up to manufacture the finer traces design. Firstly, partly copper is plated on CCL and then electroplating with covering areas that do not need to be plated. The dry film has good plating resistance is attached to the surface of CCL. And then, cover with positive film (the non-transparent portion is a pattern to be retained), the dry film is irradiated with UV light, and then uncovered dry film will polymerize, and then transfer the pattern on the dry film. The unpolymerized dry film will polymerize was dissolved using solution , circuit pattern will appear while leaving exposed dry film. The copper is electroplated and plating tin on the copper to protect the pattern from etching away. Next the polymerized dry fil is removed and the undesired copper is visualized, and etched away by solution, will get the cricruit traces which has protected by tin. The final process will remove tin.