Solder Pad Recommendations for Surface-Mount …

1 SBFA015A - January 1998 - Revised May 2003 Application PAD Recommendations FORSURFACE- mount DEVICESBy Wm. P. Klein, and performance requirements continue to push thepackaging of electronic systems into smaller and smallerspaces. At one time, the standard center-to-center pin spac-ing was 100 mils ( ") on through-hole parts (DIPs).The advent of Surface-Mount devices (SMD) has brought pinspacings that differ from one package series to the Solder joint of pin-foot to printed circuit board (PCB) mustprovide the strength to hold the device in place.

2 The closelead spacings make lead-to-lead Solder bridges more preva-lent. These factors increase the importance of an optimizedPCB criteria for a well-designed Solder joint is based on bothempirical data and reliability testing. Solder -joint strength isdirectly related to the total Solder volume. An observablesolder fillet is evidence of proper wetting. Therefore, apositive Solder fillet is usually specified. A joint can bedescribed by the Solder fillets formed between the devicepins and the PCB pads. Figure 1 shows the three fillets: toe,heel, and properly designed Solder pad minimizes Solder bridgingwhile affording a strong and easily inspected goals have conflicting dimensional to consider when determining the dimensions of thesolder pads include part dimension tolerances, PCB produc-tion tolerances, and accuracy-of-placement 2 shows how placement accuracy can affect solderbridge formation.

3 The designer should also consider thelimitations of the soldering process. Boards designed forwave soldering usually have slightly wider pads than thosedesigned for reflow trade organizations provide industry standards. The Elec-tronic Industries Association (EIA)1 represents manufacturers inall areas of the electronics industry. The EIA s Joint ElectronDevice Engineering Council (JEDEC)2 establishes standardpackage dimensions. The Institute for Interconnecting andPackaging Electronic Circuits (IPC)3 has established standardsfor PCB design.

4 The Surface mount Land Pattern Subcommit-tee of the Printed Board Design Committee of IPC has devel-oped standard pad dimensions for the packages defined by theJEDEC committee. The IPC document Surface-Mount Designand Land Pattern Standard is designated further assist the designer, the mathematical relationshipsin the standard have been programmed in a spreadsheetcalculator. Access to this program is available at the IPCHeelToeSideFIGURE 1. Solder Joint 1998-2003, Texas Instruments 2. Device Joint Joint Joint I. Assumed Basic : (1) Electronic Industries Association (EIA)2500 Wilson BoulevardArlington, VA 22201 (2) Joint Electron Device Engineering Council (JEDEC) (3) The Institute for Interconnecting and PackagingElectronic Circuits (IPC)2215 Sanders RoadNorthbrook, IL 60062-6135 Phone: 847-509-9700 Fax: 847-509-9798 web site3.

5 Surface-Mount land patterns are given formany JEDEC standard packages. Capability to customizethe patterns for special designs is also provided. The resultsof this program are tabulated in the appendices of this paperfor some of the more popular packages currently supplied byTexas values listed in the following tables are based on theassumptions shown in Table I. Performance will also dependon process variables. While an effort has been made toselect nominal values for these variables, the design engi-neer should determine the optimum value through LWWTTAABBHHPLEADPACKAGE# II.

6 Package Dimensions 3. Package LWWTTAABBHHPLEADPACKAGE# III. Package Dimensions 4. Pad # IV. Pad Dimensions # V . Pad Dimensions ( ) ( ) ( ) ( )EXSOT223 FIGURE 5. SOT223 Package Dimensions Inches (mm).FIGURE 6. PCB Pad Dimensions for SOT223 Inches (mm). ( ) ( ) ( ) ( ) ( )# OFPKGA AND EBXLEADS DESIGNATORFIGURES 5 AND 6 FIGURE 5 FIGURE ( ) ( ) ( ) ( ) ( ) ( )TABLE VI. Dimensions for SOT-223 Inches (mm).NOTE: Pad sizes are the minimum recommended and maybe increased for improved heat DEVICESThe three DDPAK Surface-Mount power package types allhave the same body dimensions.

7 They differ only in thenumber of leads and their associated lead values are given in Table VIII.# OFPKGA AND EBXLEADS DESIGNATORFIGURES 5 AND 6 FIGURE 5 FIGURE ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )TABLE VII. Dimensions for DDPAK Inches (mm).NOTE: Pad sizes are the minimum recommended and maybe increased for improved heat 8. PCB Pad Dimensions for DDPAK inches (mm). ( ) ( ) ( ) ( )FIGURE 7. DDPAK Package Dimensions Inches (mm). ( ) ( ) ( ) ( ) ( )BIMPORTANT NOTICET exas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications,enhancements, improvements, and other changes to its products and services at any time and to discontinueany product or service without notice.

8 Customers should obtain the latest relevant information before placingorders and should verify that such information is current and complete. All products are sold subject to TI s termsand conditions of sale supplied at the time of order warrants performance of its hardware products to the specifications applicable at the time of sale inaccordance with TI s standard warranty. Testing and other quality control techniques are used to the extent TIdeems necessary to support this warranty. Except where mandated by government requirements, testing of allparameters of each product is not necessarily assumes no liability for applications assistance or customer product design.

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