Appeal 2006-1454
Application 09/004,524
Patent 5,483,421
13. Referring to Figure 1, a somewhat diagrammatic or schematic
representation of a ceramic chip carrier 10 mounted on a glass filled epoxy organic
circuit card 12 by means of solder ball connections 14 is depicted (col. 4, ll. 2-6).
14. Figure 2 shows the pattern of relative normal displacement between
the card and the chip carrier, which describes the deflection of the card and the
resulting strain in each solder ball under the same 60° C temperature change.
15. Figure 3 shows the stress in the plane of the module (col. 6, ll. 10-14).
16. From an examination of Figures 1, 2, and 3, it can be seen that when a
ceramic carrier is attached to an organic circuit board and the temperature of the
structure is changed, a significant amount of stress is introduced into the unit. This
stress is carried by or impressed upon the solder ball connection (col. 6, ll. 15-20).
17. Applicants state at column 6, lines 20-31, that:
[I]n order to resist this stress, i.e. to prevent failure of the unit at the
solder ball joints 14 or at their connection to the bonding pads on the
chip or carrier, the solder balls have to be of sufficient size and
strength and the bonds to the pads sufficiently strong or reinforced to
withstand the strain without failure. Thus, the solder balls need to act
not only as an electrical connector for the chip carrier and circuit
board in the relaxed or unstrained condition, they must also act as
mechanical structural elements that are "plastic" in nature to prevent
the induced differential expansion movement of the card and the chip
carrier transmitting sufficient stress to cause failure of the structure.
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