Conductive epoxy bumps

Conductive Epoxy Bumps Placed on the Newly Formed Bond Pads... 

Figure 5.15 Conductive epoxy bumps on redistributed bonding pads.

Conductive Epoxy Bumps Conductive Epoxy Bumps... 

Flip-chip devices have solder bumps, other metal bumps, or even conductive adhesive bumps on the face of the device for I/O connections. During assembly, the devices are flipped face down, then mated and bonded to corresponding solder or metal pads on the package or interconnect substrate. In the quest to eliminate tin-lead solders, electrically conductive epoxy adhesives are beginning to be used for the bumps. 

Once the epoxy bumps have been formed, the wafer is thinned from the backside, the devices are singulated, and their edges beveled at 45° to expose gold pads at the periphery of die. The chips are then stacked and bonded with thermally conductive, electrically insulative epoxy (Figure 5.16). Paste adhesives are cost effective and can be dispensed with existing epoxy dispensing equipment. However, with... 

Other characteristics of electrical interconnects are current-carrying capacity and interconnect resistance. Current-carrying capacity is important for the qualification of adhesives for flip-chip interconnects. Typical cmrent densities for conductive epoxies used as flip-chip bumps are 10-20 A/mm and typical bump resistances are 12 mQ. 

Figure 32 Process for the fabrication of polymer bumps (a) bumping sites delineated by screen printing silica-filled polyimide paste (b) silver-filled epoxy resin composition is printed over the metal pads (c) polymer bumps are formed by screen printing a second layer of conductive epoxy. Steps (d) and (e) sketch the subsequent flip chip process using a layer of conductive adhesive coated on the substrate bonding pads.

A conductive epoxy adhesive is screen printed over the connecting pads of the wiring board on top of which the integrated circuit carrying gold stud bumps is flip... 

In a similar process, known as polymer-film interconnect (PFI), an insulative thermoplastic film is laminated over the devices at the wafer stage, and vias are opened over the bonding pads using a laser. At that point, either the normal solder bumps can be formed or a silver-filled conductive adhesive can be stencil printed into the vias to form polymer bumps. After printing, the epoxy is B-staged and the flip-chip devices are diced. In assembly, the devices are heated to a temperature that completes the cure of the B-staged bumps and simultaneously reflows the thermoplastic underfill material. 

Flip-chip bonding Screen or stencil printable or z-axis (anisotropic conductive), or isotropic conductive bumps. anisotropic and isotropic conductive pastes or films, underfill epoxies or modified epoxies... 

Figure 40 Flip chip process using gold stud bumps and epoxy conductive adhesive (1) silicon substrate (2) silicon dioxide (3) metal bonding pad (4) silicon nitride passivation (5) stud gold bump (6) silver-filled epoxy adhesive (7) metal bonding pad (8) printed...

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