1 - Al Kossow's Bitsavers

Surface Mount Component AvailabilityMost IC manufacturers are presently producing surfacemountcomponents for a large part of their product line. Thedevices available range from the sophisticated VLSI to thediscrete transistor. Non-integrated circuit components rangingfrom chip resistors and capacitors to surface-mount connectorsare also being produced in volume by major manufacturers.As the demand for surface-mount components increases,most products now produced for standard throughholetechnology will also be available in surface mount. Asof the printing of this application report TI produces over700 ICs in surface mount packages.Surface mounting consists of five basic steps:1. PC board design2. Solder paste application3. Component mounting4. Oven drying (optional)5. Solder retlowA brief description of each step will be given; detaileddescriptions of the various steps can be obtained by componentand equipment suppliers and from numerous technicalarticles on surface mounting.PC Board DesignTo produce reliable surface-mount PC boards the designerhas to pay particular attention to IC solder pad (also termedfootprint) layout. Not providing adequate footprint area andproper orientation will generally yield poor solder joints andlack of self-centering during retlow. Figure 5 shows therecommended footprints for the I8-pin PLCC. When layingout the IC footprints, as a general rule the footprint shouldextend approximately 10-15 mils past the outer edge of thePLCC lead. This provides a good solder fillet that will extendup the outer edge of the PLCC lead to yield a reliablesolder joint that is easily inspected. The 70-80 mil lengthof the footprint should be a minimum, however a longer footprintcan be used. It is recommended that the dimensionsA and B never be less than the minimum width or lengthof the IC.l>"C'2.,.Cr... mci"~en:r .....0~3... ms·~A8.81 (0.347)8.05 (0;317)~r0.762 (0.030)00.635 (0.025)L ( )T ( )( )( )... J.... ""-12.03 (0.080)1.78 (0.070)00000 00 0 0( )( )( )( )~......12.4 (0.487)11.6 (0.457)BFigure 5. I8-Pin PLCC Footprint9-20