BACKGROUND OF THE DISCLOSURE

This disclosure relates generally to methods for attachment of electronic components to a substrate or lead frame, and more specifically to methods incorporating sintering materials that are used to perform such methods.

Sintered silver die attach films combine unique physical properties of nanosilver powder and innovative chemical formulations into innovative products that allow joining various electronic devices to produce extremely reliable high thermal and electrical conductivity interfaces. Reference can be made to U.S. Patent Application Publication No. 2012/0114927 A1, which is incorporated herein in its entirety for all purposes, for processes in which sintered silver die attach films are uniquely positioned to fit into existing manufacturing equipment and processes to enable high volume manufacturing. This technology covers wide variety of devices and applications from large area thyristors and power modules for electrical and automotive equipment to miniature discrete components for mobile technology and LED lighting. The technology improves performance of existing devices by either increasing power or light output or reliability as compared to traditional joining techniques. The sintering films enable use of the new high temperature SiC and GaN semiconductors and new device designs that produce electrical efficiency unattainable with the existing technologies.

Silver die attach pastes and films are the joining materials that attach an electronic device to a passive substrate or to another device. A silver film is unique because it can be applied or laminated to an individual die, to the back side of the die or to the wafer. In one embodiment, the die is placed on the preheated substrate with a force sufficient to densify the film and establish intimate connection between the material and the connected parts. Under the applied heat and pressure, the film sinters and connects the die to the substrate. The resulting joint between the die and the substrate is metallic silver with the structure and properties shown with reference toFIG. 1.

In many semiconductor packages, an electrical connection of the device is provided through clip bonding to the top of the die. This arrangement ensures low electrical resistance of the package and improved performance compared to wire bonding. Clip bonding is done by soldering a copper clip to one or both bond pads and their corresponding leads. The process typically uses high lead solder material and requires a good control of the soldering process, especially the positioning of the die and clips during the molten phase of the solder reflow process.

SUMMARY

A process for die and clip attachment using sinterable silver films is well suited for high volume manufacturing of discrete packages. The process utilizes technology of dispensable tack agent to position the dies and clips on the lead frame before sintering. The clips can also be used in a matrix connected to a lead frame. The following sintering step can be done in any commercially available sinter press.

In one aspect of the present disclosure is directed to a method of die and clip attachment comprising: providing a clip, a die and a substrate; laminating a sinterable silver film on the clip and the die; depositing a tack agent on the substrate; placing the die on the substrate; placing the clip on the die and the substrate to create a substrate, die and clip package; and sintering the substrate, die and clip package.

Embodiments of the present disclosure further may include laminating the sinterable silver film with an application of a pressure of 2-3 MPa or higher and a temperature of 130° C. applied for 30 seconds. The die can be laminated individually or as a whole wafer followed by dicing. The clip can be laminated individually or in the form of a copper plate followed by dicing or stamping. Laminating the sinterable silver film can be done in a lamination press capable of providing specified pressure and temperature or in a die bonding machine. The laminated die may be collected and stored in a waffle pack or on a dicing tape. The laminated clip may be collected and stored on the tape, reel or waffle pack. The tack agent may be dispensed on the substrate to place and held in position the components of the package before the components have been moved to the sintering press. The tack agent provides temporary attachment of the die and the clip to the substrate. The tack agent evaporates during the sintering of the substrate, die and clip package without interference with the sintering process. The die may be placed on the substrate with a die bonder, and secured in the position with the tack agent. The clip may be placed on the substrate with a pick and place machine or an epoxy die bonder, and secured in the position with the tack agent. Sintering the substrate, die and clip package may include a sintering press having a pressure tool and a heated platen. Sintering may include application of a pressure of 10 MPa and a temperature of 250° C. for 60 seconds. Clips may be laminated with the sinterable silver film in a form of a matrix connected to the substrate. A spacing between the clips may be matched to the dies positioned on the substrate. A solder joint can be created by the method described herein. A clip can enables a uniform transfer of pressure to a die and a foot pad of a substrate.

