K6c. tape automated bonding (TAB) - is a means of electrically connecting chips to circuit boards, other substrates or packages. Instead of using fine gold or aluminum wires to connect chips, TAB utilizes thin, flat metal conductors that are mounted on a tape of polyimide film. The tape facilitates the positioning of the conductors to pads on the chip. The copper conductors are either deposited as a layer on the tape by using sputtering or vacuum deposition, or made from a layer of copper foil. The copperlead pattern in the layer is produced by photolithographic processes or by mechanical blanking. The copper conductors are then plated with nickel for corrosion protection, and with gold to facilitate bonding. A window opening is made in the tape for bonding the inner leads to the chip, and another for bonding or soldering the outer leads. The windows are made either by blanking before the foil is added, or by chemical blanking after the leads are in place. Fig. 13K6c illustrates the tape with leads affixed, and shows the means of bonding the leads to a chip. Bonding to the chip is the first connection. Thermo-compression bonding is used to connect the inner leads to gold bumps on the pads of the chip. One tool, called a thermode, provides the heat and pressure for all chip connections simultaneously. The operation is highly automatic and quick. After bonding of the tape to the chip, the chip is normally covered with a liquid resin encapsulant that, when the resin hardens, provides protection to the chip and the connections. Another advantage of TAB is that the tape connecting leads are very thin, helping provide a low profile for the IC, if that is needed. The other ends of the tape leads are connected to the circuit board or other substrate by one of several methods: reflow soldering, conductive adhesives, or thermo-compression bonding. A portion of the plastic tape backing is retained.

Fig. 13K6c Tape automated bonding (TAB) of an integrated circuit chip: a) a plan view of the copper leads affixed to a polyimide tape with window openings for connection to a chip and later for connection to a package substrate or circuit board. b) a cross section of the chip bonded electrically to the copper leads with a protective resin coating over the chip and the connections.

K6d. flip-chips - constitute a method for connecting integrated circuits to printed circuit boards with no wire leads and very short connections. The design facilitates the operation of high speed devices such as PC microprocessors. With this method, the chip is first connected to the substrate of the IC package. Solder bumps are provided on the top of the chip by plating, or by stenciling solder paste on the connection pads and then reflowing. The chip is inverted (“flipped”) and positioned on the package substrate. Pads on the substrate match the spacing and position of the bumps on the chip. The chip is then reflow soldered again to connect the chip circuits to the substrate. The balance of the package then can be assembled to the chip. There is a small space between the pads on the chip and the pads on the substrate so that the solder connection is almost spherical in shape. This provides some flexibility in the connection. The substrate has internal wiring channels that connect to underside wiring pads, which are larger and more widely spaced than the pads on the chip and the top of the substrate. These pads are used to connect the packaged chip to the circuit board, using the ball grid array method. Solder spheres are positioned and held in place on the circuit board with a tacky flux. When these spheres are reflowed, a very short connection with minimum capacitance effects is achieved. Fig. 13K6d illustrates the completed arrangement.

For added reliability of the solder joints, some flip chips receive underfilling . This involves the addition of a plastic encapsulant to the solder joint area. The encapsulant helps to distribute stresses caused by thermal cycling of a group of solder joints. Epoxy or silicone resins in low-viscosity form are dispensed to the joint from hollow needles and flow into the space between the solder bump connections by capillary action. Jet dispensing is also used.

Curing temperatures are in the 280 to 360 ° F (140 to 180 ° C) range.

Fig. 13K6d Example of a flip-chip connected to a circuit board with a solder sphere ball grid array.