Patent Application
20150305145
This disclosure relates to bulk metallic glasses and more particularly to methods of joining bulk metallic glasses useful for, for example, electronic packaging.
Metallic glasses are metal alloys with non-crystalline microstructures. They are typically obtained by fast quenching from the molten state, which hinders crystallization. The preparation of metallic glass foil of an Au—Si alloy was first reported in 1960. Noble metal alloy metallic glass rods around 1 mm in diameter were reported in the mid-1970s to 1980s. Interest in metallic glasses increased rapidly in the late 1980s and 1990s, however, when bulk metallic glasses (BMGs), greater than a few mms in diameter, were successfully prepared from alloys of common metals.
The disordered atomic structure, lack of grain boundaries, and metastable state of metallic glasses leads to unique properties. Metallic glasses conduct electricity like conventional metals, but deform and fail brittly in tension, similar to conventional glasses. Typical carriers of plastic flow, dislocations, are not present leading to high tensile strengths and elastic limits but different kinds of failure modes than conventional metals. The formation of metallic glass composites, by either mixing in or precipitating a second phase within the glassy matrix, has been reported as a method for tuning the mechanical, thermal, and electrical properties of these materials.
Like conventional glasses, metallic glasses exhibit a glass transition temperature (Tg) and crystallize at a temperature (Tx) above Tg. Within this supercooled liquid region (SCLR, Tx-Tg), metallic glasses can be thermo-plastically formed into precise and complex shapes using methods similar to those used for conventional glasses—e.g. compression molding, blowing, embossing. They can also be cast directly into molds and quenched to a glassy state with very low shrinkage.
These properties of BMGS have made them attractive for applications in aerospace, naval, sports equipment, electronic packaging, MEMS and biomedical devices. In order to enable the applications in most of these fields, it would be advantageous to have joining technologies which enable two BMGs or BMGs and other classes of materials to be joined.
One embodiment is a method comprising:
Another embodiment is a bulk metallic glass submount comprising:
One such joining technology which may be suitable for electronic packaging is disclosed here. Further disclosed is an application for BMGs in the fields of micro- or opto-electronics packaging. Some embodiments may provide substrates with good CTE match to GaN, while also having good thermal stability, chemical durability, and surface polish characteristics. Further advantages may be ease of package formability or significant cost savings due to reduced bill of materials and less process steps. This is advantageous because in some products, 70-80% of the cost is the bill of materials. If the application of the product is in consumer electronics where cost is a factor, BMG packaging may provide a significant advantage. Further, the BMG joining methods disclosed herein are compatible with standard soldering materials and process equipment.
A new joining process is disclosed and an application for bulk metallic glasses (BMGs). A method to join a semiconductor material or any other class of material with bulk metallic glass through soldering is also disclosed. The BMG can be coated with Cr—Ni followed by dull-sulfamate nickel and then with Au. The other material is recommended to have gold coating on the face that is going to be joined to the BMG. In some embodiments, the other face has the three layers described above. In semiconductors like GaAs, the metallization is Ti/Pt/Au, in InP, the metallization typically followed is Ti/W/W etc. There are several other combinations but these are examples. The solders can be pre-deposited on the substrate after the cap layer, for example, Au or the solder can be in the form of a pre-form layer.
The two materials can be joined using soldering. Solders that can be used include any conventional solders that are routinely used in micro-electronics and opto-electronics packaging such as eutectic Au—Sn, SAC305, SAC405 etc. The application disclosed is that the entire opto-electronics package can be formed from a BMG by taking advantage of the ease of formability of BMGs. This may eliminate the need for substrates, the need for processes to attach the substrates and sub-mounts, package bases etc. The whole package would be just one single piece comprised of a BMG.
Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.
Reference will now be made in detail to various embodiments of glass-ceramics and their use in LED articles, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.
Apart from the chip, there are three additional components: hybrid, molybdenum block, and package base. In a typical package, there are primarily four process steps: solder attachment between the chip and the hybrid, solder attachment between the hybrid and the molybdenum block, solder attachment between the molybdenum block and the package base, and finally wire-bonding. Each of the components has to be coated separately to facilitate the soldering processes.
Exemplary joining methods disclosed herein uses a bulk metallic glass to form the whole base structure 200 as shown in
For convenience, this structure is referred to herein as the “BMG package structure”. The composition of the bulk metallic glass 20 can be selected from any system which exhibits good glass formability (large critical thickness). Critical thickness (tmax, in mm) is the maximum thickness that an alloy can be cast into and still remain amorphous. This thickness is related to the critical cooling rate (Rc, in deg K/s) of the alloy (i.e. how fast it must be quenched to be amorphous) through the expression Rc˜1000/tmax2. Thus, if a 2 mm thick part is required, the alloy needs to have an Rc˜250 K/sec or for a 3 mm thick part, Rc-100 K/sec) including, for example, Zr-based alloys (e.g. Zr55Al10Ni5Cu30, Zr52.5Cu17.9Ni14.6Al10Ti5), noble metal-based alloys (e.g. Pd40Cu30Ni10P20), Cu-based alloys (e.g. Cu49Zr45Al6) , rare-earth based alloys, and Ti-based alloys.
Further shown in
One embodiment, an example is shown in
Another embodiment is a bulk metallic glass submount comprising:
An exemplary method for joining a semiconductor chip to the BMG package is as follows: first a surface of the bulk metallic glass onto which the semiconductor chip is to be attached is prepared. The bulk metallic glass is deposited with Cr—Ni coating using, for example, an evaporation technique. An entire surface or a portion of a surface of the bulk metallic glass can be coated. This is followed by nickel flash and then gold coating. For the solderable applications, dull sulfamate nickel deposits can be used. Sulfamate nickel deposits provide the corrosion resistance. After these steps, there are two options, for example, a solder preform can be used or solder can be pre-deposited onto the coated BMG. This can facilitate soldering of the semiconductor chip to the BMG.
In some embodiments, an insulating layer, e.g. SiN, is deposited on the uncoated portion of the BMG surface and Au pads are coated which can serve as pads for wire-bonding. In some embodiments, only one component and two joining process steps (chip-attach to BMG package structure and wire-bonding) are needed and may result in cost savings through reduced bill of materials, process time, and number of steps. The chip reliability will not be compromised if the CTE of the BMG material is tailored to that of semiconductor chip and the thermal conductivity is sufficiently high (e.g. ˜200 W/m-K).
As an example, a bulk metallic glass substrate was formed and joined to a GaAs chip using the disclosed methods. A BMG substrate of a Zr-based metallic glass, Zr52.5Cu17.9Ni14.6Al10Ti5, was made by the following method. Pieces of high purity Zr, Cu, Ni, Al, and Ti wire were weighed in an Ar-purged glovebox. The metals were arc melted in a clean Ar atmosphere on a water-cooled copper hearth to form a button of the alloy. The button was remelted 3-4 times in order to homogenize the material. The alloy button was then re-melted in the arc melter and suction cast into a water-cooled copper mold with dimensions 1.5 mm×8 mm×30 mm. The as-cast BMG was polished on one surface.
The Tg of the Vit105 BMG was measured by DSC-TGA as ˜395° C. and Tx (onset) as ˜453° C. The BMG substrate was cleaned and metalized or coated. Next, these BMG substrates were coated with Cr—Ni followed by dull-sulfamate Ni and then Au coated. Eutectic Au—Sn solder preforms were cut into the required shape and sandwiched between the BMG substrate and the semiconductor chip. This multi-layer stack was held tight with the chip and was carefully transferred to a solder reflow oven. The highest temperature in the oven was 320° C. and was cooled down to room temperature. This is because the melting point of the Au—Sn solder is 280° C. Once the bond was formed, the soldered assembly was removed from the solder reflow oven and, as a first step, a needle was poked at the chip to make sure it was strongly adhered to the substrate. Next, one of the assembled samples was loaded into the dage machine and a shear test was performed. The shear force required to shear off the chip was approximately 0.5 Kg.
It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.
This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 61/731,146 filed on Nov. 29, 2012, the entire content of which is hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US13/71433 | 11/22/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61731146 | Nov 2012 | US |
