Patent Application
20060234427
The invention relates to the manufacture of integrated circuit assemblies. More particularly, the invention relates to the dispensation of underfill material between an IC device and a substrate.
Semiconductor devices are subject to many competing design goals. Since it is very often desirable to minimize the size of electronic apparatus, surface mount semiconductor devices are often used due to their small footprint. Solder nodules or “bumps” having spherical, near-spherical, or other shapes are frequently used to join an IC to a substrate, such as a printed circuit board (PCB). The IC and substrate have corresponding metallized locations generally known as contact points, or bond pads. The components are aligned, typically using sophisticated optical aligning tools. Solder bumps positioned at the prepared metallized locations are heated, and solder bonds are formed between the contact points upon cooling. When completed, the IC-to-substrate assembly solder joints are typically “blind,” that is, they are not readily accessible for visual inspection. Often the gap between the IC and substrate is filled with a dielectric underfill material. The IC assembly is then encapsulated in a protective plastic package in order to in order to provide increased strength and protection.
Among the problems encountered with packaged IC assemblies, some of the most common and debilitating are the separation of layers, and open or short circuits caused by separation of materials, or the ingress of moisture between separated materials. For these reasons, void-free underfill processes and materials are highly desirable. Various combinations of underfill materials, dispensing patterns, and flow techniques have been used in efforts to reduce the formation of voids and reduce underfill process time. Common underfill dispensing techniques include “I” pass dispensing as shown in the cut-away view of an IC assembly 10 of
Problems persist in the efforts to achieve void-free underfills while optimizing throughput. Leaving aside the properties of the underfill fluid itself, the geometry of the die, substrate, and solder bumps in an assembly also have an effect on underfill fluid flow rate and coverage. In general, smaller vertical gaps increase flow rate and larger horizontal distances tend to reduce flow rate. The flow rate is also increased as the density of solder bumps increases, due to the stronger capillary action provided by the increased surface area. Fillets are often formed at the edges of the die-substrate gap during the underfill process. Dispensing a relatively large volume of underfill material can enhance flow, assure an adequate supply of fluid, and reduce voids, but excessive fillet size can increase stress on the edges of the completed package. Generally, stress increases with distance from the center of the die, and the larger the die, the greater the stress. Efforts to increase flow rate by force such as pumps and vacuums are sometimes successful. However, in addition to increasing flow rate, prevention of void formation is a challenge. Voids form when air becomes entrapped by the flowing underfill material. Flow rate, flow pattern, temperature, drag, and fluid viscosity are all intertwined in the completion of the underfill process and in the potential formation of voids. Many instances of void formation can be attributed to the differences in flow rate in different areas of an assembly. For example, in assemblies such as those shown in
Due to these and other problems, improved methods for the manufacture of integrated circuit assemblies with reduced potential for underfill voids and increased throughput would be useful and advantageous in the arts.
In carrying out the principles of the present invention, in accordance with preferred embodiments thereof, IC assemblies are provided with underfill using methods designed to decrease the propensity for void formation.
According to one aspect of the invention, a method for dispensing underfill material into the gap between a die and substrate of an IC assembly includes steps for providing an aperture in the substrate for receiving underfill material into the gap. Underfill material is dispensed into the gap through the aperture, filling the gap with underfill material with a reduction in the propensity for the formation of voids.
According to another aspect of the invention, a method for dispensing underfill material through a substrate aperture to fill the gap between a substrate and die uses capillary action.
According to yet another aspect of the invention, a method for dispensing underfill material through a substrate aperture to fill the gap between a substrate and die uses the application of force to the underfill material.
According to still another aspect of the invention, a method for dispensing underfill material through a substrate aperture to fill the gap between a substrate and die uses the application of force with a vacuum.
According to another aspect of the invention, a method for dispensing underfill material through a substrate aperture to fill the gap between a substrate and die uses the application of positive pressure.
According to one aspect of the invention, a method for dispensing underfill material into the gap between a die and substrate of an IC assembly includes steps for providing an aperture in the substrate for receiving underfill material into the gap wherein the aperture is positioned in the approximate geographic center of the substrate and material is dispensed into the gap through the aperture.
According to yet another aspect of the invention, a method for dispensing underfill material into the gap between a die and substrate of an IC assembly includes steps for providing more than one aperture in the substrate for receiving underfill material into the gap. The underfill material is dispensed into the gap through the apertures.
The invention has advantages including but not limited to improved underfill material dispensing and IC assemblies with improved strength and resistance to stress. These and other features, advantages, and benefits of the present invention can be understood by one of ordinary skill in the arts upon careful consideration of the detailed description of representative embodiments of the invention in connection with the accompanying drawings.
The present invention will be more clearly understood from consideration of the following detailed description and drawings in which:
References in the detailed description correspond to like references in the various drawings unless otherwise noted. Descriptive and directional terms used in the written description such as first, second, top, bottom, upper, side, etc., refer to the drawings themselves as laid out on the paper and not to physical limitations of the invention unless specifically noted. The drawings are not to scale, and some features of embodiments shown and discussed are simplified or amplified for illustrating the principles, features, and advantages of the invention.
In general the invention provides methods for underfill dispensing in the manufacture of semiconductor device assemblies.
Those reasonably skilled in the arts will recognize that various alternatives exist for the adaptation of the methods of the invention to specific applications. For example, the dispensed underfill material 12 may be flowed using capillary action or may be assisted using force applied to the underfill material 12 such as by a vacuum or by pressurized dispensing means. Although the aperture 32 shown in the examples of
The methods and apparatus of the invention provide advantages including but not limited to promoting electrical and mechanical bonding in IC assemblies. While the invention has been described with reference to certain illustrative embodiments, those described herein are not intended to be construed in a limiting sense. It will be appreciated by those skilled in the arts that the invention may be used with various types of semiconductor device packages. Various modifications and combinations of the illustrative embodiments as well as other advantages and embodiments of the invention will be apparent to persons skilled in the arts upon reference to the drawings, description, and claims.
