Patent Application
20070029653
The invention relates to the field of microelectronics and more particularly, but not exclusively, to the application of autonomic self healing composites to integrated circuit packaging.
The evolution of integrated circuit designs has resulted in higher operating frequency, increased numbers of transistors, and physically smaller devices. This continuing trend has generated ever increasing area densities of integrated circuits and electrical connections. To date, this trend has resulted in both increasing power and increasing heat flux devices, and the trend is expected to continue into the foreseeable future. Further, materials used in electronic packaging typically have various coefficients of thermal expansion. Under temperature fluctuations, the various coefficients of thermal expansion may lead to mechanical failures such as cracking and delamination. Still further, mechanical failures may be induced by many other causes, e.g. exposure to shock and vibration during shipping to a system or motherboard integrator, system or motherboard assembly, or shock and vibration during delivery to the end customer.
Often, solder bumps electrically and mechanically couple an integrated circuit die to a package substrate. Further, the package substrate may be electrically and mechanically coupled to a printed circuit board by solder balls. The package substrate may have a coefficient of thermal expansion different from the die and/or the printed circuit board. Under a change in temperature, a mechanical stress may result within the solder balls and solder bumps due to various coefficients of thermal expansion. In some circumstances, the solder balls and solder bumps crack under the thermally induced stress. Once a crack initiates, the crack may propagate at a rate partially dependent on a characteristic dimension of the crack, e.g., diameter at the tip of the crack.
One existing method of preventing solder ball and solder bump cracking includes dispensing a curable material in the regions between the solder balls and solder bumps (“underfilling”). When an underfill is used, some of the stress otherwise taken by the solder balls and solder bumps is taken by the underfill material and thereby reduces the likelihood of solder ball or solder bump cracking. Under the present method, if a crack initiates within the underfill, the crack may propagate through the underfill and through the solder ball and solder bump. Often underfill materials may be brittle, and thus cracks propagate readily once they initiate. In another existing method, underfill materials with increased toughness may be used to slow crack propagation. Though a crack in a brittle underfill may propagate rapidly, even a crack in a tough underfill material may still propagate.
In other circumstances, adjoining layers of material within the package may delaminate due to a mechanical stress transferred through the solder balls and solder bumps. Similar to crack propagation, a region of delamination may propagate at a rate partially dependent on a characteristic dimension of the region of delamination. One well known method of partially managing delamination failures includes applying an adhesive coating to a material interface. Similar to crack propagation, delamination may more readily propagate when an interface coating is brittle than when the interface coating is tough. Likewise, while delamination propagation in a tough interface coating may be slower than in a brittle interface coating, the delamination failure may still propagate.
Material cracking and delamination may occur under circumstances other than expansion and contraction due to temperature cycling. Circumstances under which cracking and delamination failures may occur are many. They include, among others, for example, dynamic warpage of the package during use, fatigue from temperature cycling, shock and vibration arising from shipping, assembly, and handling.
Herein disclosed are a method for including, and an apparatus and system that includes, an autonomic, self-healing material that may arrest delamination and crack growth.
In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. Other embodiments may be utilized and structural or logical changes may be made without departing from the intended scope of the embodiments presented. It should also be noted that directions and references (e.g., up, down, top, bottom, primary side, backside, etc.) may be used to facilitate the discussion of the drawings and are not intended to restrict the application of the embodiments of this invention. Therefore, the following detailed description is not to be taken in a limiting sense and the scope of the embodiments of the present invention is defined by the appended claims and their equivalents.
Reference to “monomers” means monomers, and chain extended forms of monomers, capable of polymerizing upon mixing with other monomers and monomer systems.
Reference to “monomer systems” means a group of two or more monomers that may polymerize upon mixing.
As in
Embodiments of the encapsulated resin 102 may include epoxy resins. Alternative embodiments may include isocyanate resins. Further embodiments of epoxy resins and isocyanate resins may include, among other compounds, bisphenol-A diglycidl ether, chain extended forms of bisphenol-A diglycidyl ether, bisphenol-F diglycidyl ether, chain extended forms of bisphenol-F diglycidyl ether, novolac glycidyl ether, cresol-novolac glycidyl ether, cycloaliphatic moieties, long chain aliphatic moieties, DER 354, DER 332, DER 330, DER 732, DER 736, aromatic diisocyanates, aliphatic diisocyanates, toluene diisocyanate, hydrogenated diisocyante, methylenediphenyl diisocyanate, hydrogenated methylenediphenyl diisocyanate, Desmodur N3200, Desmodur N3300, Desmodur DA, Desmodur DN, equivalents thereof, or a combination thereof.
Embodiments of the encapsulated hardener 104 may include polyols, polyamines, diamines, Ancamide 2137, Ancamide 2349, Ancamide 2353, Ancamide 2424, Ancamide 2445, Ancamide 1637, Ancamide 2089M, Demophen 550U, Multranol 9109, Baycoll ND 2060, Hardener OZ, equivalents thereof, or a combination thereof.
Still other embodiments of monomer systems may include cyanate esters, vinyl or acrylic resins with free radical initiators (e.g., peroxides), and silicone rubbers (e.g., PDMS, RTV).
An embodiment of a self healing material applied at an interface of materials with different properties may retard delamination. Exemplary embodiments of self healing materials applied to an interface of different materials may include an interface between a die-attach and die and a mold compound to underfill. Other embodiments may exist and the partial listing of embodiments is not meant to be limiting. An embodiment of a self healing material applied at an interface between and underfill 308 and a die 312 may slow or prevent delamination cracks from damaging circuits within the package 300 by filling the cracks with monomers that polymerize prior to, or during, crack propagation. Shown in
An embodiment of a self healing material may be used as underfill material. One embodiment of an underfill is a die underfill. Alternative embodiments of self healing materials used as underfill may include underfill to a substrate solder resist and underfill to a die passivation layer. Other embodiments of underfill materials may exist and the partial listing of alternatives is not meant to be limiting.
For an embodiment similar to the embodiment depicted in
Although specific embodiments have been illustrated and described herein for purposes of description of an embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve similar purposes may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. For example, an alternative embodiment may exist where a layer of self healing material may be used between a die and integrated heat spreader. Another embodiment may apply a self healing underfill material between a package substrate and printed circuit board. Yet another embodiment may exist wherein a self healing material forms an underfill of solder balls on a chip scale package. Further, encapsulated monomers may be dispersed through out a material forming part of an underfill, a mold compound, a die-attach, or a stress compensation layer.
Those with skill in the art will readily appreciate that the present invention may be implemented using a very wide variety of embodiments. This detailed description is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.
