1 - Al Kossow's Bitsavers

INTRODUCTION TO SURFACE MOUNT TECHNOLOGYABSTRACTThe demand for high-density, cost-effective printed circuitboards has prompted the electronics industry to seek alternativemethods to traditional plated-through-hole technology.One such alternative is surface mounting, a technology traditionallyused in hybrid fabrication. The advantages· of surfacemounting are numerous but the bottom line is that itis cost effective and will begin to displace plated-throughholetechnology as the a~ailability of surface-moUlit componentsincreases.Texas Instruments is fully supporting the growth of thesurface-mount industry with its line of plastic leaded chipcarriers. An introduction to the surface-mount technologywill be given in this application report.INTRODUCTIONThe post molded leaded chip carrier (pLCC) wasdeveloped by Texas Instruments in 1980 to improve the packingdensity of ICs on printed circuit (PC) boards and overcomesome of the size constraints normally caused by dualin-line(DIP) packages. The PLCC was also designed to beused under the same environmental conditions as the DIPwithout any reliability degradation. The PLCC occupies approximately40% to 60% of the PC board area of anequivalent DIP, and requires no through holes (surfacemount), therefore, it lowers the cost on PC boards. Unlikesome surface-mounted packages, TI's PLCC requires nospecial PC board material considerations. The design of thelead provides compliance allowing the use of any commercialsubstrate. Digital, Linear, Gate Array, and MOS deviceswill be offered in 18-, 20-, 28-, 44-, 52-, 68-, and 84-pinpackages through TI.Package OutlineThe mechanical data for the PLCCs is given in Figures1 and 2; their thermal properties are listed in Table 1. Thefollowing general statements apply to the packages:1. Each of the chip carrier packages consists of a circuitmounted on a lead frame and encapsulated within anelectrically nonconductive plastic compound. The compoundwithstands soldering temperatures with no deformation,and circuit performance characteristics remainstable when the devices are operated in high humidityconditions.2. These packages are intended for surface mounting onsolder pads with 1,27-mm (0.050-inch) centers. Theleads require no additional cleaning or processing whenused in soldered assembly.3. All dimensions shown are metric units (millimeters),with English units (inches) shown parenthetically. Inchdimensions govern.4. Lead spacing shall be measured within the zonesspecified.5. Tolerances are noncumulative.6. Lead material CD-155. T60 (Copper Alloy).7. Dimple in top of package denotes pin 1.s::::o'+IaJ...E.....o.Etns::::o'+IaJCJ'=a•0.~9-15