Glass Serves as Wafer Level Packaging

Company News

A new company, Inspectech Ltd. (Carmiel, Israel), has been formed to produce equipment for inspecting diced 300 mm wafers.

F&K Delvotec (Ottobrunn, Germany) is shipping an order for Model 6400 wire bonders to Hewlett Packard (Colorado Springs, Colo.). The company received orders for Model 6400 and Model 4400 die bonders from RF Monolithics (Dallas, Texas).

PADS Software (Marlborough, Mass.), along with InterChip Systems (North Andover, Mass.), re-leased a new package layout software line, PowerBGA. The first offering focuses on direct chip attachment to PC boards and will expand to BGAs, CSPs and laminate MCMs.

Integrated Packaging Assembly Corp. (IPAC, San Jose, Calif.) has obtained a $7.5 million commitment for equipment financing. Immediately available was $3 million, with the remainder to become available after IPAC raises an additional $10 million in equity or other financing.

ESEC (Asia Pacific) Pte. Ltd. (Singapore, Malaysia) signed a $30 million contract to supply wire and die bonders to PT Astra Microtronics Technology (AMT, Batam, Indonesia). The agreement covers equipment deliveries from July 1998 through June 2000.

Walsin Advanced Electronics (Kaosiung, Taiwan), Winbond Electronics (Hsinchu, Taiwan), Toshiba Corp. and Mitsui & Co. (Tokyo, Japan) are funding a new company, Walton Advanced Electronics Ltd. (WAE, Kaohsiung, Taiwan), to assemble 64 Mb DRAM and other memory devices.

Glass Serves as Wafer Level Packaging

ShellCase Ltd. (Jerusalem, Israel) has developed a wafer level chip scale packaging technology, ShellPack, in which a thinned die is sandwiched between two glass plates. The "shell" is 300 to 500 mm thick and no more than 100 mm longer or wider than the die. It is intended for ultrathin applications like smart cards and portable products. It is also being offered as a replacement for direct chip attach (DCA). The packaged device is said to have 15% greater break resistance than bare silicon of the same thickness.

The wafer is bonded to a glass plate, and it is lapped down to a 100 mm thickness. Etching is then performed to thin the wafer to 50 mm and to separate the dice (Figure). Another glass plate is bonded to the backside of the devices, encapsulating the devices in epoxy. The assembly is then flipped, and grooves are made in the front side glass, exposing the I/O pads on the devices. Metal is evaporated on the front side and patterned to make the I/O connections.

Since the package completely encases the die in adhesive, the die is protected on all sides before the devices are singulated. The packaged device is about the same size and thickness as a bare die, but it does not require as much care in handling. With the glass and a choice of a transparent epoxy, optoelectronic devices can be packaged without special windows.

ShellCases's technology starts by bonding a wafer face down onto a plate of glass (a). After thinning and singulation by etching, a second plate is bonded to the back, encapsulating the devices in adhesive (b). Grooves are made in the first plate, exposing the bond pads on the dice, and metal is deposited and patterned for the I/Os (c) before singulation.

One practical concern for smart cards is reverse engineering. Many believe that the software technology used on smart card chips is sufficient to defeat "black box" reverse engineering of a stolen card. However, if the card is taken apart and the chip removed, the chip can be reverse engineered with available equipment. The ShellPack package is designed to be resistant to being opened. The company claims that it cannot be taken apart without destroying the chip.

Testing and burn-in of the devices is done at the wafer level, so the packaged parts are ready to use. The leads are also very short, reducing parasitics and improving electrical performance. Thermal paths to air or to a heat sink are also very short, aiding in heat removal. The package can be attached to a PC board using conventional soldering rather than TAB or wirebonding, so the part requires no additional contact area.

Lead counts for a 12.5312.5 mm die in this package can be as high as 320. Peripheral and BGA configurations may be used with lead pitches from 0.3 to 0.5 mm. For high heat dissipation applications, aluminum nitride can be used instead of glass.