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# Measurement Method of FCA Joint Resistance adopting a Four-Terminal Circuit

IP.com Disclosure Number: IPCOM000015179D
Original Publication Date: 2002-Apr-11
Included in the Prior Art Database: 2003-Jun-20
Document File: 2 page(s) / 91K

IBM

## Abstract

"Measurement Method of FCA Joint Resistance adopting a Four-Terminal Circuit" is a new method that can detect a minute breakdown of FCA joints connecting power source or ground of a SLC circuit board with that of a bare chip. The outlook of this method is shown in figure-1. In this figure, (A) is a FCA joint for power source or ground that should be measured. On the other hand, (B) and (C) are ones for random signals. (D), (E), (F) and (G) are BGA joints. It is the most important thing that (A), (B) and (C) are connected to each other through the dummy bare chip. First, a constant current I is passed through (D)-(B)-(A)-(E) and the voltage difference V between (G)-(C)-(A)-(F) is measured. Then, when the resistance between (a)-(b)-(c) is defined as R, ther following equation stands up because the constant current I is neither passed through (G)-(a) nor (c)-(F) but (a)-(b)-(c) ;

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Measurement Method of FCA Joint Resistance adopting a Four-Terminal Circuit

"Measurement Method of FCA Joint Resistance adopting a Four-Terminal Circuit" is a new method that can detect a minute breakdown of FCA joints connecting power source or ground of a SLC circuit board with that of a bare chip.

The outlook of this method is shown in figure-1. In this figure, (A) is a FCA joint for power source or ground that should be measured. On the other hand, (B) and (C) are ones for random signals. (D), (E), (F) and (G) are BGA joints. It is the most important thing that (A), (B) and (C) are connected to each other through the dummy bare chip.

First, a constant current I is passed through (D)-(B)-(A)-(E) and the voltage difference V between
(G)-(C)-(A)-(F) is measured. Then, when the resistance between (a)-(b)-(c) is defined as R, ther following equation stands up because the constant current I is neither passed through (G)-(a) nor (c)-(F) but (a)-(b)-(c) ;

R=V / I

And further, because wiring between (b)-(c) is made of copper and its resistance is extremely small and can be ignored, the resistance R is almost equal to that of FCA joint (A).

An example wiring in a dummy bare chip is shown in figure-2. In this figure, power source and ground pads are located along the chip edges and diagonals and each of them is connected to two random signal ones.

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