BRIEF DESCRIPTION OF THE DRAWINGS
In order to facilitate a fuller understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be exemplary only.
FIG. 1 is a table of IMC thickness and Nickel (Ni) layer consumption of aged pure Indium (In) and 2% Germanium (Ge)/Indium (In) samples in accordance with an embodiment of the present disclosure.
FIG. 2 shows a scanning electron microscopy (SEM) picture, magnified ×1000, of a pure Indium (In) sample on a Nickel (Ni)/Gold (Au) substrate aged for 1000 hrs at 150° C. in accordance with an embodiment of the present disclosure.
FIG. 3 shows a scanning electron microscopy (SEM) picture, magnified ×1000, of a 2% Germanium (Ge)/Indium (In) sample on a Nickel (Ni)/Gold (Au) substrate aged for 1000 hrs at 150° C. in accordance with an embodiment of the present disclosure.
FIG. 4 shows a scanning electron microscopy (SEM) picture, magnified ×3000, of a 2% Germanium (Ge)/Indium (In) sample on a Nickel (Ni)/Gold (Au) substrate aged for 1000 hrs at 150° C. in accordance with an embodiment of the present disclosure.
FIG. 5 is a table of IMC compositions of aged pure Indium (In) and 2% Germanium (Ge)/Indium (In) samples in accordance with an embodiment of the present disclosure.
FIG. 6 shows a graph of oxide formed in a 85° C./85% relative humidity chamber for pure Gallium (Ga) and 0.05% and 0.1% Germanium (Ge)-doped Gallium (Ga) in accordance with an embodiment of the present disclosure.
FIG. 7 shows a graph of oxide formed in a 85° C./85% relative humidity chamber for 0.5%, 1%, 2%, and 5% Germanium (Ge)-doped Gallium (Ga) in accordance with an embodiment of the present disclosure.
FIG. 8 shows a graph of oxide formed in a 85° C./85% relative humidity chamber for 0.0001% and 0.0005% Germanium (Ge)-doped Gallium (Ga) in accordance with an embodiment of the present disclosure.
FIG. 9 shows a graph of oxide formed in a 85° C./85% relative humidity chamber for Gallium (Ga)/Indium (In) alloys with and without 0.5% Germanium (Ge) in accordance with an embodiment of the present disclosure.
FIG. 10 shows a graph of oxide formed in a 85° C./85% relative humidity chamber for Indium (In)/Bismuth (Bi) alloys with and without 0.5% Germanium (Ge) in accordance with an embodiment of the present disclosure.
FIG. 11 shows a graph of oxide formed in a 85° C./85% relative humidity chamber for Gallium (Ga) alloys containing 0.5% Phosphorus (P), 0.5% Titanium (Ti), 0.5% Manganese (Mn), and no dopants in accordance with an embodiment of the present disclosure.
FIG. 12 is a table of relative peak intensity of Germanium (Ge) to Gallium (Ga) with different laser power for 2% Germanium (Ge)/Gallium (Ga) in accordance with an embodiment of the present disclosure.
FIG. 13 shows a graph of ICP-MS spectrum of 2% Germanium (Ge)/Gallium (Ga) for 15% laser power in accordance with an embodiment of the present disclosure.
FIG. 14 shows a graph of ICP-MS spectrum of 2% Germanium (Ge)/Gallium (Ga) for 25% laser power in accordance with an embodiment of the present disclosure.
FIG. 15 shows a mounting configuration wherein a metallurgical bond is formed between a pad of an electronic component and a pad of a substrate through an interconnecting material, such as solder, in accordance with an embodiment of the present disclosure.
FIG. 16 shows an application of a TIM in an electronic assembly in accordance with an embodiment of the present disclosure.
FIG. 17 shows a simplified example of a first TIM in the form of a phase change material, a thermally conductive gel, a thermally conductive tape, or a thermal grease that comprises a polymeric matrix filled with a thermally conductive filler between an IHS and an electronic component in accordance with an embodiment of the present disclosure.
FIG. 18 shows an example wherein a first TIM is a PSH where a thermally conductive filler stays as a liquid at service temperature and a polymeric matrix gives mechanical adhesion between an IHS and an electronic component in accordance with an embodiment of the present disclosure.
FIG. 19 shows an example wherein TIM material may be placed directly between an IHS and an electronic component without a polymeric matrix in accordance with an embodiment of the present disclosure.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Alloy compositions and techniques for reducing IMC thickness and oxidation of metals and alloys in accordance with embodiments of the present disclosure are described. Such alloy compositions and techniques were discovered through experimental testing. For example, in order to solve problems of solder joint reliability, an IMC growth test was used to reveal a technique for preventing IMC growth of interconnect material such as solder and TIM in accordance with an embodiment of the present disclosure. That is, significant, unprecedented effects were observed when IMC growths of 2% (wt) Germanium (Ge)/Indium (In) and pure Indium (In) on an electrolytic Nickel (Ni)/Gold (Au) substrate after aging in a 150° C. oven for 1000 hours. IMC thickness and Nickel (Ni) layer consumption of samples were measured after aging the samples. As shown in the table of FIG. 1, total IMC thickness of pure Indium (In) was about 18.8-19.6 microns while the IMC thickness of 2% Germanium (Ge)/Indium (In) was about 2.0-3.4 microns. The original thickness of Nickel (Ni) layer of the substrate was 5.3 microns and the Nickel (Ni) layer consumption of samples with pure Indium (In) and 2% Germanium (Ge)/Indium (In) were determined as 45.3-49.1% and 3.8-7.5%, respectively. FIGS. 2 and 3 show scanning electron microscopy (SEM) pictures of a pure Indium (In) sample and a 2% Germanium (Ge)/Indium (In) sample, respectively, on an electrolytic Nickel (Ni)/Gold (Au) substrate after aging in a 150° C. oven for 1000 hours. The decrease in IMC in the 2% Germanium (Ge)/Indium (In) sample is readily apparent. When seen at higher magnification, it is also apparent that the IMC consists of three layers (see FIG. 4).
In order to understand the mechanism for thinner IMC in germanium-doped indium, energy dispersive spectrometry (EDS) is helpful and thus was performed. The table of FIG. 5 summarizes EDS analysis results for the pure Indium (In) sample and the 2% Germanium (Ge)/Indium (In) sample.
Summarizing, as shown in FIG. 2, only one layer of IMC is found in the pure Indium (In) sample. However, as shown in FIGS. 3 and 4, three layers of IMC are found in the 2% Germanium (Ge)/Indium (In) sample. As shown in the table of FIG. 5, the composition of the IMC in the pure Indium (In) sample was determined to be (Ni, Au)28In72, Meanwhile, the composition of the first IMC layer (i.e., closest to solder) of the 2% Germanium (Ge)/Indium (In) sample was determined to be 54% Indium (In), 32% Nickel (Ni), 13% Germanium (Ge), and 1% Gold (Au). It should be noted, however, that the actual composition of the first IMC layer of the 2% Germanium (Ge)/Indium (In) sample may not be precisely accurate because the first IMC layer of the 2% Germanium (Ge)/Indium (In) sample was thinner than the measurement resolution. Thus, materials in areas other than the first IMC layer of the 2% Germanium (Ge)/Indium (In) sample may be included in the composition of the first IMC layer of the 2% Germanium (Ge)/Indium (In) sample. The second IMC layer of the 2% Germanium (Ge)/Indium (In) sample, however, was thicker than the first IMC layer of the 2% Germanium (Ge)/Indium (In) sample and thus it was possible to determine the exact composition of the second IMC layer of the 2% Germanium (Ge)/Indium (In) sample as (Ni, In, Au)50Ge50. The composition of third IMC layer of the 2% Germanium (Ge)/Indium (In) sample was same as the composition of the IMC in the pure Indium (In) sample.
It is believed that Germanium (Ge) reacts with Nickel (Ni) in the early stages of aging to form Germanium (Ge)-rich IMC layers and that these Germanium (Ge)-rich IMC layers protect the Nickel (Ni) layer from reaction with solder. It is also believed that when a certain IMC layer forms a dense and stable layer that can block inter-diffusion between solder and a substrate material, thinner total IMC and less consumption of the substrate material such as for UBM is observed. Thus, it is further believed that formation of such a protective IMC layer results in better reliability. From the discussion above, it may be concluded that the thin layer(s) of Germanium (Ge)-rich IMC plays a role as diffusion barrier to slow down solder diffusion to substrate.
In order to solve problems of oxidation of metals, including low melting temperature metals, an oxidation test was used to reveal a technique for preventing oxidation in accordance with an embodiment of the present disclosure. Indeed, the above-described significant, unprecedented effects of Germanium (Ge) were also observed in low melting temperature metals such as gallium in the oxidation test. That is, samples of low melting temperature metals 99.95% Gallium (Ga)/0.05% Germanium (Ge), 99.9% Gallium (Ga)/0.1% Germanium (Ge), and pure Gallium (Ga) were placed in a 85° C./85% relative humidity chamber. Metal oxide formed on top of the metals in a vial. The amount of oxide was determined by measuring the height of the oxide part (volume) formed on top of the metals. The amount of oxide for the pure Gallium (Ga) sample increased rapidly and showed about 90% oxide in 10 days. In contrast, the samples of Gallium (Ga) containing small amounts of Germanium (Ge) showed much slower oxidation rates. Indeed, the 99.95% Gallium (Ga)/0.05% Germanium (Ge) and 99.9% Gallium (Ga)/0.1% Germanium (Ge) samples didn't show a significant amount of oxide until after 80 days in the 85° C./85% relative humidity chamber (see FIG. 6).
To see if higher concentrations of Germanium (Ge) may give better oxidation properties, samples of Gallium (Ga) containing 0.5, 1, 2, and 5% (wt) Germanium (Ge) were tested. As shown in FIG. 7, there is no big improvement by using higher concentrations of Germanium (Ge).
To check for a lower limit of the effective amount of Germanium (Ge), 0.0001% Germanium (Ge)/Gallium (Ga) and 0.0005% Germanium (Ge)/Gallium (Ga) were tested. As shown in FIG. 8, only a slight effect was observed for these alloys.
Gallium (Ga)/Indium (In) is a eutectic alloy and thus may also be a good thermal interface material. The anti-oxidation effect of Germanium (Ge) on such an alloy would therefore be of interest in view of the above findings. Therefore, the oxidation rate of a 78.6% Gallium (Ga)/21.4% Indium (In) alloy was compared with a 0.5% Germanium (Ge)/78.2% Gallium (Ga)/21.3% Indium (In) alloy. As shown in FIG. 9, the Germanium (Ge)-containing Gallium (Ga)/Indium (In) alloy showed a much more stable oxidation property.
Bismuth (Bi)/Indium (In) is also a eutectic alloy and thus may also be a good thermal interface material. The anti-oxidation effect of Germanium (Ge) on such an alloy would therefore be of interest in view of the above findings. Therefore, the oxidation rate of a 66.7% Indium (In)/33.3% Bismuth (Bi) alloy was compared with a 0.5% Germanium (Ge)/66.4% Indium (In)/33.1% Bismuth (Bi) alloy. As shown in FIG. 10, only a slight anti-oxidation effect was observed for the Germanium (Ge)-containing Indium (In)/Bismuth (Bi) alloy.
For comparison purposes, the anti-oxidation effect of other dopants on Gallium (Ga) would be of interest in view of the above findings. Therefore, the oxidation rate of 0.5% Phosphorus (P)/Gallium (Ga), 0.5% Titanium (Ti)/Gallium (Ga), and 0.5% Manganese (Mn)/Gallium (Ga) were compared with pure Gallium (Ga). As shown in FIG. 11, some anti-oxidation effect was observed for the Phosphorus (P), Titanium (Ti), and Manganese (Mn)-doped Gallium (Ga), but not as much as Germanium (Ge)-doped Gallium (Ga).
The mechanism for using Germanium (Ge) to protect Gallium (Ga) from oxidation was investigated. It was assumed that a thin Germanium (Ge)-containing protective layer was formed and that this layer protected further reaction of Gallium (Ga) with oxygen. A laser ablation ICP-MS method was used to verify this mechanism. The laser ablation ICP-MS method is widely used for surface composition analysis. During this method a high energy laser ablates a small area of the surface of a sample. The ablated material is then transferred into an ICP-MS analysis chamber. The higher the laser intensity, the deeper the ablation.
When lower laser power (15%) was used so that the ablation was shallow, the relative intensity of the Germanium (Ge) major peak (68.8-68.9) was 31-32% to the Gallium (Ga) major peak (68.8-68.9) for 2% Germanium (Ge)/Gallium (Ga). When the higher laser power (25%) was used, the relative intensity of Germanium (Ge) was 8-10%. The results give qualitative evidence that the Germanium (Ge) atoms go to the surface to protect the alloy from oxidation. The test has repeated at a different spot of the sample and showed the same result. FIGS. 12-14 show the analysis results.
Referring to FIG. 15, there is shown a mounting configuration wherein a metallurgical bond is formed between a pad 2 of an electronic component 1 and a pad 4 of a substrate 5 through an interconnecting material 3, such as solder, in accordance with an embodiment of the present disclosure. IMC layers build up between the solder interconnecting material 3 and the component pad 2 and/or the substrate pad 4. The compositions described herein may reduce IMC growth between the solder interconnecting material 3 and the component pad 2 and/or the substrate pad 4 to increase reliability of the electronic component 1.
Referring to FIG. 16, there is shown an application of a TIM in an electronic assembly in accordance with an embodiment of the present disclosure. The electronic assembly comprises a substrate 5 connected to an electronic component 1 through interconnecting material 10. An integrated heat spreader (IHS) 8 is attached to a top side of the electronic component 1 using a first TIM 9 to dissipate heat generated from the electronic component 1. The IHS 8 is also connected to a heat sink 6 by a second TIM 7 for further dissipation of heat.
One of the most effective materials for the first TIM 9 and the second TIM 7 is a thermal solder such as indium, indium alloys, gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, indium-lead alloy, indium-lead-silver alloy, bismuth-tin alloy, and indium-tin-bismuth alloy. The compositions described herein may reduce IMC growth between the electronic component 1 and the IHS 8 and/or between the IHS 8 and the heat sink 6 to increase reliability.
Referring to FIG. 17, there is shown a simplified example of the first TIM 9 in the form of a phase change material, a thermally conductive gel, a thermally conductive tape, or a thermal grease that comprises a polymeric matrix 12 filled with a thermally conductive filler 11 between the IHS 8 and the electronic component 1 in accordance with an embodiment of the present disclosure. The conductive filler 11 may include indium, indium alloys, gallium, gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, cadmium, cadmium alloys, indium-lead alloy, indium-lead-silver alloy, mercury, mercury alloys, bismuth-tin alloy, and indium-tin-bismuth alloy. The compositions described herein may improve oxidation properties and reduce reactivity of the thermally conductive filler 11.
Referring to FIG. 18, there is shown an example wherein the first TIM 9 is a PSH where a thermally conductive filler 13 stays as a liquid at service temperature and the polymeric matrix 12 gives mechanical adhesion between the IHS 8 and the electronic component 1 in accordance with an embodiment of the present disclosure. The thermally conductive filler 13 may include indium, gallium, gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, cadmium, cadmium alloys, indium-lead alloy, indium-lead-silver alloy, mercury, mercury alloys, bismuth-tin alloy, and indium-tin-bismuth alloy. The compositions described herein may improve oxidation properties and reduce reactivity of the thermally conductive filler 13.
Referring to FIG. 19, there is shown an example wherein TIM material 15 may be placed directly between the IHS 8 and the electronic component 1 without the polymeric matrix 12 in accordance with an embodiment of the present disclosure. The TIM material 15 may be liquid metal such as gallium or low melting point metals or alloys. A confiner 14 may be used to prevent the TIM material 15 in liquid form from leaking out from between the IHS 8 and the electronic component 1. The compositions described herein may improve oxidation properties and reduce reactivity of the TIM material 15.
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.
Patent Application
20070256761
