Epoxy bumps

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

Figure 5.15 Conductive epoxy bumps on redistributed bonding pads.

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... 

Conductive Epoxy Bumps Conductive Epoxy Bumps... 

A similar structure to the structure discussed in JP-A-63281460 above is disclosed in JP-A-63296272. In the latter, the HgCdTe wells are not connected by indium bumps but by Au films supported by an epoxy resin. 

A substrate 10 of HgCdTe having detectors 14 and 16 and bumps 20, 22, 24, 26 and 28 is shown. The substrate is bump bonded to a second read-out substrate 18 having bumps 30, 32, 34, 36 and 38 thereon. A dam member 46 extends vertically between the two substrates so as to prevent the flow of epoxy 40 from entering into the region around detectors 14 and 16. The epoxy, when hardening, will draw the substrates closer together in the areas near the detectors but not in the areas of the detectors. 

In an alternative embodiment, channels 22 are etched through the detector layer 16 and into the transparent substrate 14 to a depth slightly exceeding the required thickness. The detector array portion and the silicon circuit 12 are bonded together by the aid of indium bumps 18, and an epoxy material 20 is back-filled into the space between the detector array portion and the read-out chip. 

The structure is bonded to a substrate 24 which is chosen to have a coefficient of thermal expansion that is selected for providing the resultant read-out chip assembly with an effective coefficient of thermal expansion that is approximately the same as an HgCdTe detector array 36. The substrate material may be GaAs (4.5-5.9 x 10"6 m/mK), CdTe, Ge (5.5-6.4 x 10"6 m/mK), and a-plane sapphire (3.5-7 5 x 10" m/mK) where the coefficients of thermal expansion are given in parentheses. The coefficients of thermal expansion for silicon, HgCdTe and epoxy are 1.2 x 10"6 m/mK, 3.8-4.5 x 1 O 6m/mK and 30-50 x 10"6 m/mK, respectively. Next, the substrate 16 is removed and aluminium pads 34a are formed. Indium bumps 34b are cold welded to corresponding indium bumps 36b. 

As with most items on a vacuum line that contain mercury, place the Toepler pump in a secondary container that is firmly attached to another surface to contain any mercury that may spill from an accident as well as protect the pump from accidental bumps (see Fig. 7.28). Plastic containers (such as plastic milk cartons) are particularly good because the mercury will not affect plastic. Conversely, mercury may amalgamate with the metals in a metal can, which could destroy any containment capabilities. In addition, it is easier to get mercury out of a plastic container (with smooth walls) than out of a metal one (with a narrow rim). The plastic tub can be glued onto the table with some epoxy. The epoxy will stick better if you roughen up the bottom surface of the plastic container with sandpaper. Because not all epoxies stick to plastic, test the epoxy before assuming that it will hold. 

Tertiary amine salts of DMP-30 provide extended room temperature pot life (6 to 10 h at 20°C) when used at concentrations of 10 to 14 pph in liquid DGEBA epoxy resins. They cure at moderately elevated temperatures (4 to 8 h at 60°C), or even at room temperature with a heat bump. The acid moiety blocks the tertiary amine centers and deactivates them. The salt then dissociates on heating, freeing the amine groups, which are then able to react with the epoxy group. 

Quarry Tile Tile is used in much of the food process and food preparation areas, also toilet and change areas. In general, it is installed without an asphaltic membrane but with a thin adhesive membrane usually an epoxy type. As noted above, the concrete substrate must be true to line without irregularities such as humps and bumps. All such flaws will telegraph through to the finished surface. Cleanliness is a major attribute of the quarry tile installation. For example, in a synthetic elastomer plant the raw latex when spilled stuck tightly to the concrete floors. Quarry tile was used with an epoxy bed and a furan joint (very narrow, Vie"). Due to the greater density of the quarry tile the unvulcanized material cleaned up easily. 

Choice of adhesive. Use neoprene adhesive for applications where vibration, bumps, etc., are encountered such as over-the-road trailers. For higher temperatures epoxy is preferred. Neoprene-based adhesive should be allowed to dry to touch before the sheets are applied over it. Neoprene adhesive is used for application temperature not exceeding 107°C while epoxy adhesive is used for up to 121°C. It is important to note that adhesive can become a weak link in an otherwise strong chain. 

Table 8. The effect of a 5 mln/150 degree C post UV thermal bump on the film properties of epoxy acrylate and AM...

One way in which vinyl ether monomers may be used is as reactive diluents in epoxy systems. The addition of a vinyl ether greatly increases the cure speed of the system. The rapid change to a tack-free state appears to be the result of the polymerization of the vinyl ether component of the mixture. A "thermal bump" Is still necessary to cure the epoxy and bring the coating to a fully cured state(16). There is little evidence for any copolymerization of the vinyl ether and the epoxy groups. 

Winchester discs are molded as blanks in engineering plastics, usually General Electric s Ultem polyetherimide, then coated with an epoxy-ferric oxide layer. The main requirement in manufacturing these discs is absolute flatness because the magnetic read/write head moves only 8-20 microinches above the disc surface and is spinning at a high speed of 3,600 rpm. Any microscopic bump can thus cause damage to both the disc and head. 

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. 

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. 

Fill the vias by screen printing or stencil printing sufficient silver-filled epoxy to form bumps or leave the vias open for wire bonding. 

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. 

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