Patriot American Solutions’ Surface Mount Technology (SMT) Process

As the components used in assemblies become smaller the stencils have smaller and smaller apertures. Just a small piece of residue can cause problems for 0201 or 01005 size components.  To overcome the issues due to hand cleaning, PAS has an automated stencil cleaner (shown in the Cleaning Room).

The clean stencil is next placed in the stencil printer. The bare assembly board comes out of the de-stacker and is conveyed into the printer where solder paste is squeegeed through the stencil onto the board and forms the SMT pattern.

The conveyor then sends the patterned board to the stencil printer inspection machine that checks the printed board for positioning of the pads and also the volume of solder paste for each. This is important because an error here just requires a re-cleaning and re-printing.  There are no components involved to be lost.

The printed circuit board continues down the line to our fast machine, where the common components that are in 8MM reels and usually passives, meaning resistors, diodes, and common capacitors, are picked and placed.  These represent approximately 90% of the placed components and can be placed at 30,000 components per hour.

The circuit board is then conveyed to the next pick and place station that is called the flexible placement machine for larger components and IC’s.  It usually places 10% of the SMT components and has a speed of 15,000 components per hour with direct tray feed, large reel feeders, and vibrating tube feeders.

Now all of the SMT components are in solder paste and ready to enter the nine-stage reflow oven to run each different assembly through its particular profile.  Once this assembly has been run, its profile remains in the reflow oven’s memory for future runs. Having passed through the oven, the board is both populated and soldered.

The assembly is conveyed to the final line process and into the automatic optical inspection or AOI where part values and polarities are checked.  PAS also checks the solder joints with visual inspection as the AOI, which is based on optics, cannot accurately discern solder joint integrity.