Tape Automated Bond (TAB)
Tape Automated Bonding involves bonding a gold bumped die to a single layer circuit built on a flexible material, such as polyimide. TAB is used primarily in the flat panel display industry to mount driver chips between the glass of the display and the input circuitry behind the display. The flexible circuit used in TAB allows for the package to be bent up to 180'. TAB is also utilized as a package format for Multi Chip Modules (MCM). In this format, the die and some of the leads are punched from the tape, the leads are formed, and the package is mounted similar to a J-Lead package. In some cases, the leads are not formed, but are soldered directly to the board. Chip Supply is supplying programs in the flat panel display industry and MCM industry with TAB product. See Fig. 1 for an example of a punched TAB circuit.

Figure 1

TAB Technology Overview
TAB is typically a single sided polyimide based circuit, although two-metal tape is available. Copper is either electro-deposited to the tape or rolled copper is attached to the tape using an adhesive. The circuitry is then imaged using a photolithography process. The main advantage of TAB is the tight pitch of the circuit. Currently, line pitches of 45 microns are achievable (22.5 micron lines/spaces). This allows for high-density circuits for high pin count devices.

The polyimide film comes in three widths, 35 mm, 48 mm and 70 mm. This allows for different size circuits to be built maximizing a certain area. The other critical dimension is length of the part, which is typically measured in sprocket pitches (see Fig. 1). Each sprocket pitch is equal to 4.75 mm. Most exposure systems can produce a maximum circuit size of 16 pitches (76 mm). The base polyimide film is typically in the range of 50 to 100 microns thick.
The key to TAB processing is that the circuit traces can be cantilevered over holes punched into the tape. A hole is punched in the tape where the device is to be bonded, and leads are cantilevered over to match the position of each gold bump on the die. Similarly, the leads can cantilever over other punched holes to allow for solder of the package to a board, or to punch the leads out of an opening to form the package. See Fig. 2 to see a TAB lead bonded to a gold bump.

Figure 2
Bend windows can be punched in the tape that allows for the tape to be folded. In the case of a flat panel display, the bend windows match the position of the folds, which allow for the tape to bonded on the front side of a glass panel, and folded around the glass to attach to a PCB behind the glass.
Chip Supply's TAB Capabilities

Chip Supply currently supplies TAB in both JEDEC and reel-to-reel formats to the flat panel display and MCM markets. JEDEC tape is usually used in high reliability applications where burn-in and environmental testing is required. Reel to reel is typically employed in higher volume cost sensitive applications. Thermosonic bonding using Hughes single point bonders is offered in JEDEC format only. Thermo-compression bonding using Shinkawa gang bonders is offered in both JEDEC and reel-to-reel formats. Custom TAB/TCP design and assembly services are available today.