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1、Application Report SZZA031 - December 2001 1 A Nickel-Palladium-Gold Integrated Circuit Lead Finish and Its Potential for Solder-Joint Embrittlement Donald Abbott, Douglas Romm, Bernhard LangeStandard Linear multiply by 1.5 to allow for heel filet = 1.575 mm. b. Foot width is 0.51 mm. c.Foot thickne
2、ss is 0.15 mm. d. Surface area Foot area is 1.575 0.51 = 0.8033 mm2. Edge area is (assuming fillet goes to top) (1.575 2) + 0.51 0.15 = 0.549 mm2. e. Total soldered surface area per lead is 1.3523 mm2 per lead. 3. Calculated thickness of Au for 3 weight % Au in joint a. 6.59 104 g Sn per pad 0.03 =
3、1.3523 mm2 per lead 19.32 g/cm3 (Au density) 1 cm3/1000 mm3 Au thickness in mm b. Solve for Au thickness in mm = 7.57 104 mm or 0.757 ? or 7570 c.Nominal thickness in production does not exceed 50 . To get to the 3 weight % Au level, Au thickness would exceed the minimum by 150, if there were no Au
4、on the PWB pad. Part B. Thickness Data on PWBs and Components Used in Study The XRD/EDX data are for the PWBs and the components evaluated in this study. Ten leads per component were evaluated, except as noted. PWB pads (see Table A1) Table A1. XRD/EDX Data PWB PADS THICKNESS OF Au (?) (Au ?) AVERAG
5、EMAXMINSD 5 NiAu0.550.670.480.04 Std NiAu0.200.280.090.05 SZZA031 20A Nickel-Palladium-Gold Integrated Circuit Lead Finish and Its Potential for Solder-Joint Embrittlement Devices (see Table A2) Table A2. XRF/EDX Data COMPONENTS THICKNESS OF Au () COMPONENTS AVERAGEMAXMINSD 3000 289343252225722 150
6、18025012542 18353337303 Sub-50- data obtained by EDX NOTE 1:1 ? = 10,000 = 10 103 mm Part C. Calculations of Au Concentration in Parts Used in the Study This part gives calculations of the percentage of Au in the joints we made, accounting for the Au on the PWB pads. The averages of measured Au valu
7、es are used in the calculations. 4. Boards (see Table A3) a. Pad size is 0.7 mm 1.4 mm = 0.98 mm2. b. Au thickness on board 38a is 0.55 ? or 5.5 104 mm. c.Au thickness on board 39a is 0.20 ? or 2.0 104 mm. d. Mass of Au on 38a is 0.98 mm2 5.5 104 mm 1 cm3/1000 mm3 19.32 g/cm3 = 1.04 105 g Au/pad. e.
8、 Mass of Au on 39a is 0.98 mm2 2.0 104 mm 1 cm3/1000 mm3 19.32 g/cm3 = 3.79 106 g Au/pad. 5. Components (see Table A4) a. Total soldered surface area per lead is 1.3523 mm2. b. For the nominal 3000- leads: 1.3523 mm2 2.893 104 mm 1 cm3/1000 mm3 19.32 = 7.56 106 g Au/lead c.For the nominal 150- leads
9、: 1.3523 mm2 1.80 105 mm 1 cm3/1000 mm3 19.32 = 4.70 107 g Au/lead d. For nominal 30- leads: 1.3523 mm2 3.3 106 mm 1 cm3/1000 mm3 19.32 = 8.62 108 g Au/lead 6. Percentage of Au in solder joints (general formula) (see Table A5) a. Percentage of Au = (mass Au on lead + mass Au on pad)/(mass of Sn + ma
10、ss Au on lead + mass Au on pad) 100 b. Mass of solder joint = 6.59 104 g Table A3. Calculations for Boards FOR BOARDS MASS OF Au (g) THICKNESS USED IN CALCULATION (?) 38a 1.04 1050.55 39a3.79 1060.20 SZZA031 21 A Nickel-Palladium-Gold Integrated Circuit Lead Finish and Its Potential for Solder-Joint
11、 Embrittlement Table A4. Calculations for Components NOMINAL LEAD THICKNESS () MASS OF Au (g) THICKNESS USED IN CALCULATION () 30007.56 1052893 1504.70 107180 308.62 10833 Table A5. Calculated Percentage of Au in the Solder Joints ACONTRIBUTION CALCULATED WEIGHT % Au IN THE JOINT Au CONTRIBUTION FRO
12、M COMPONENT OSP Std NiAu PWB (0.28 ?) 5 NiAu PWB (0.67 ?) NiPd (no Au)00.571.55 NiPdAu (Std finish 30- Au)0.010.591.57 NiPdAu (150- Au)0.070.611.63 NiPdAu (3000- Au)1.131.702.66 NOTES:2. The contribution of the lead finish to the percentage Au in the solder joint in the 50- to 150- thickness range i
13、s 0.01 weight % and 0.07 weight %. The Au from the PWB, even at the level of 0.2-? Au on the board overwhelms the contribution of the Au on the lead. 3.The percentage of Au in a joint can be estimated from EDX data or, possibly, from a wet chemical analysis for the percentage of Au in the joint. IMP
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