[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

Although the cu thickness is not of interest it has

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Although the Cu thickness is not of interest, it has to be measured to cor- rectly calculate the spectral overlap of the Cu and Ni peaks. WinFTM can suppress the display of the Cu result if desired. Flexible pc-boards do not contain Br additives, but the design of the sample support requires particular care [256].
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594 V. R¨oßiger and B. Nensel Table 7.14. Measurement evaluation of two samples using instruments that differ in detector D and size of measurement spot M Standard deviation from a minimum of 20 single readings Sample Measuring time Measured quantity (layer) XDVM-WD: Proportional counter tube M : 0.27 mm XDALD: PIN diode M : 0.7 mm XDVM- µ SSD-MoD: PIN diode M : 0.1 mm × 0.1 mm Pc-board 20 s 86 nm Au 5 nm 4 nm 3.3 nm Au/NiP/Cu/* 4.4 µ m NiP 0.16 µ m 0.05 µ m 0.05 µ m Lead frame 100 s 5 nm Au 1.2 nm 0.8 nm 0.5 nm Au/Pd/Ni/* 30 nm Pd 2 nm 3.8 nm 3 nm 0.6 µ m Ni 0.02 µ m 0.005 µ m 0.01 µ m Small Measurement Spots for Lead-frames and pc-boards Miniaturization of Si chips and their large number of lead connections re- quires a large number of small bonding surfaces that are coated with chem- ical nickel and thin Au (Fig. 7.110). The XDVM- µ is well suited to perform these measurements; it uses an X-ray mirror as described in Fig. 7.102 for beam focusing. Due to the proportional counter tube with its large entry window, the fluorescence radiation can be detected very efficiently such that one can expect to achieve about the same precision as with the XDVM- W, in spite of the very small measurement spot (cf. Table 7.14). Using the small spot, which is very well defined in the x-direction, one can still ana- lyze the lateral thickness distribution even on such small areas as shown in Fig. 7.111. Plug-Type Connector Contacts The layer sequence is an Au/Ni/Cu-alloy or an Au/PdNi/Ni/Cu-alloy. This traditional application has changed in the course of recent times. Not only have the effective areas become smaller, the geometry may have become more complex as well [257]. For this reason, the requirement of a plane-parallel layer in the area of interaction (cf. Sect. 7.4.2 The Equipment) is essentially no longer fulfilled. With a radius of curvature < 1 mm, problems arise which however can be resolved taking certain provisions [258]. These are primarily proper positioning and an adapted measurement spot size. Another difficulty with analyzing contacts is the frequent change in sub- strate materials. Depending on the desired material properties, various alloys such as CuFe, CuZn, CuNiZn, or CuSn with varying compositions are used. This means a new “substrate material correction” (normalization for a new
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Methodological Developments and Applications 595 Fig. 7.110. Bonding surfaces of a printed circuit, overview above and detail below. The shown measurement spot of the XDVM- µ is here 40 µ m × 60 µ m substrate) has to be performed with every change of the substrate material.
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