1 - Al Kossow's Bitsavers

J-Lead AdvantageTexas Instruments PLCC packages are constructed withthe I-lead structure due to its superior performance whenmounted on a wide spectrum of substrates ranging fromceramic to epoxy-glass. This is possible due to the compliancyof the I-lead which compensates for the possible thermalmismatch between plastic packages and mounting substrates.More care must be taken when using ceramic leadless chipcarriers mounted on nonceramic substrates in order to preventsolder joint fracturing under thermal cycling. The I-leadalso offers advantages over plastic surface-mount packagesusing different lead structures. Figure 3 gives a comparisonof the I-lead used on the PLCC to the "gull wing" commonlyused on small-outline integrated circuits (SOlCs)and "quad packs."GULL WINGDEVICE AREA (16 L-PIN SOIC) = 111.6 mm 2(0.173In 2 )ADVANTAGES- PROVEN PROCESS- POSITIVE SOLDER 'WITNESS"- EASY AUTO-POSITIONING- NESTED STACKING (PERIPHERAL)DISADVANTAGES- EXTENDS X-Y SIZE- LEADS SUBJECT TO DAMAGE- HIGH PIN COUNT PACKAGES IMPRACTICALJ-LEAD:t>"C"2-n'Q)..0':sen5".., d'3...m0'::l- PROVEN PROCESSADVANTAGES- LEADS ARE COMPLIANT. USEABLE WITHPC BOARD AND CERAMIC SUBSTRATES- MINIMUM X-Y SIZE. MAXIMUM BOARD DENSITY- EASY AUTO POSITIONING- LEADS WELL PROTECTED- EASY REPLACEMENT- SOCKETING EASYDEVICE AREA (18-PIN PLCC) = 98.6 mm2- JEDEC STANDARDS EXIST- STAND-OFF FROM THE BOARD ALLOWS EASY CLEANING- LARGEST LINE OF AVAILABLE PACKAGES:FROM 18 TO 68 LEADS. HIGHER PIN COUNTS UNDERDEVELOPMENT(0.1531n2)DISADVANTAGES- TOTAL PACKAGE-HEIGHT THICKER THAN SOIC- INFRARED URI REFLOW DIFFICULTFigure 3. Gull Wing Vs. J-Lead9-18