Patent Application
20180258243
The invention relates to the field of surface treatment for a substrate, particularly but not exclusively, to a composition for adhering a polymer to a substrate, and a method of preparation of such composition.
There has been growing interest in developing surface treatment techniques for electrical and electronic circuit applications, for example, for the purpose of providing insulation between conducting layers in through silicon vias (TSVs). In traditional TSVs, although silicon dioxides have commonly been used as insulating materials, polymer-based insulation layers have recently been found to demonstrate potential advantages of much lower required process temperature, simpler fabrication process, and lower costs than silicon dioxide-based ones.
One commonly used polymer for TSV insulation is Parylene, which is the trade name for a variety of chemical vapor deposited poly(p-xylylene) polymers. Parylene is preferred due to its relatively low cost and low processing temperature when compared with the conventional TSV insulating materials such as silicone dioxide. However, one major challenge in using polymers for TSV insulation is interfacial delamination. The occurrence of interfacial delamination, especially after circuits have been subjected to a highly accelerated stress test (HAST), which is a test widely adopted in evaluating reliability and stability in electronic components and conducted at 130° C., 85% relative humidity for 96 hours, can result in open-circuits in the electronic circuits which is highly undesirable and may even be potentially dangerous.
An object of the present invention is to provide a novel composition for adhering a polymer to a substrate such that interfacial delamination at one or more polymer/substrate interfaces can be substantially minimized, reduced or avoided.
Another object of the present invention is to mitigate or obviate to some degree one or more problems associated with known adhesives for adhering a polymer to a substrate, particularly but not exclusively, for electrical and electronic applications.
The above objects are met by the combination of features of the main claims; the sub-claims disclose further advantageous embodiments of the invention.
One skilled in the art will derive from the following description other objects of the invention. Therefore, the foregoing statements of object are not exhaustive and serve merely to illustrate some of the many objects of the present invention.
In general, the invention provides a composition for adhering a polymer to a substrate, and particularly, for providing and/or enhancing adhesions between a polymer and a substrate for electrical and electronic applications. For example, the composition of the present invention can be applied to adhere and/or to enhance adhesion of one or more insulating polymers, such as Parylene, with an electrically conducting surface such as, but not limited to, one or more silicon substrates of a through silicon via (TSV). The composition can be provided in the form of, for example, a layer-like structure adapted to chemically bond with a surface of the substrate. The composition comprises at least one first compound having one or more grafter units, with each of the grafters having at least one reactive functional head group adapted to chemically react with one or more monomers in forming the polymer. Particularly, the polymerization will result in one or more polymer molecules grafted at the respective grafter sites to thereby adhere the formed polymer chains at the substrate surface. More importantly, the composition also comprises at least one second compound having one or more diluter units, which are arranged to be interspersed among the one or more grafters in the layer-like structure causing a reduction and thus optimization of the grafter density at the layer-like structure. In contrast to the grafters, the diluters do not comprise reactive functional head groups for polymerization, and therefore, are not capable of chemically reacting with the monomers. No polymer chains can thus be grafted at the sites of the diluters. The invention is shown to enable improvement in or even optimization of the grafter density in the layer-like adhesive structure, and consequently, minimize, reduce or avoid chances of premature termination of the growing polymer chains due to overly high grafter density. The invention is thus capable of significantly enhancing the interfacial bonding strength between the polymer and the substrate, and is found to be effective in minimizing, reducing, or avoiding interfacial delamination under the highly accelerated stress test (HAST)
In a first main aspect, the invention provides a composition for adhering one or more polymers to a substrate. The composition comprises at least one first compound adapted to be coated on a surface of the substrate. Said first compound comprises one or more first units each having at least one functional group adapted to chemically react with at least one monomer to form the one or more polymers. The composition further comprises at least one second compound adapted to be coated on the surface of the substrate. Said second compound comprises one or more second units interspersed among the one or more first units of the first compound; wherein each of the one or more second units is not chemically reactive to the at least one monomer.
In a second main aspect, the invention provides a method of preparing a polymer coated surface on a substrate using the composition according to the first aspect. The method comprises the steps of: providing a solution having at least one first compound and at least one second compound, the at least one first compound comprising one or more first units, and the at least one second compound comprising one or more second units; treating a surface of a substrate with the solution thereby forming a treated surface bonded with the one or more first units and the one or more second units, with the one or more first units and the one or more second units being interspersed with one another; reacting the treated surface with one or more monomers thereby grafting one or more polymers only at the one or more first units, but not at the one or more second units.
In a third main aspect, the invention provides a substrate having an intermediate layer on a surface thereof for adhesion of a polymer. Said intermediate layer comprises one or more first surface bonding units interspersed with one or more second surface bonding units, wherein only the one or more first surface bonding units are capable of chemically reacting with one or more monomers to form polymers to thereby adhere the polymers at the substrate surface.
The summary of the invention does not necessarily disclose all the features essential for defining the invention; the invention may reside in a sub-combination of the disclosed features.
The foregoing and further features of the present invention will be apparent from the following description of preferred embodiments which are provided by way of example only in connection with the accompanying figures, of which:
The following description is of preferred embodiments by way of example only and without limitation to the combination of features necessary for carrying the invention into effect.
Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments.
The present invention relates to a composition for adhering one or more polymers to a substrate, particularly but not exclusively, for providing and/or enhancing adhesions between a polymer, for example poly(p-xylene) polymers such as Parylene, and a substrate for electrical and electronic applications. The composition can be used as an adhesive for adhering and/or enhancing bonding of one or more insulating polymers, such as for the purpose of providing heat and/or electric insulation, as well as moisture barriers. Preferably, the present invention can be used as an adhering intermediate layer for polymer insulation in through silicon vias (TSVs).
Referring to
The first compound 20 may comprise one or more first units 22, which are herein referred to as, for example, grafter molecules, grafter units, or grafters 22, with each of the grafters 22 comprising at least one functional group 24, such as but not limited to, one or more ethylenically unsaturated groups adapted to chemically react with one or more monomers via, for example, free radical chain-growth polymerization. The reaction or polymerization will result in the formation of one or more polymer molecules, which will, ideally, propagate into one or more fully-grown polymer chains 50 grafted at the respective sites of the grafters 22. Generally, the polymer chains 50 will then self-assemble into a plurality of repeated domain units at the substrate surface, which allow adhesion of the formed polymers to form a polymer coating at the substrate 5. In one specific embodiment, the monomers comprise para-xylylene (p-xylylene), and the formed polymers comprise Parylene.
The second compound 30 of the composition 10 may comprise one or more second units 32, which are herein referred to as, for example, diluter molecules, diluter units, or diluters 32. Particularly, the diluters 32 are arranged so as to be interspersed among the one or more grafters 22 in the layer-like composition 10, for example, as illustrated in
The interspersed arrangement of the diluters 32 among the grafters 22 is of particular significance in minimizing, reducing, or even preventing the chances of premature termination of the growing polymer molecules, which will result in defective polymer chains with inferior physical and chemical properties. For example, a highly dense grafter population may increase the possibility for reactive sites of one or more grafter molecules to be physically blocked by one or more growing polymer chains nearby. Additionally, the reactive head group of one grafter molecule may tend to react with an adjacent reactive head group of a neighboring grafter molecule, if the grafter density exceeds a certain, optimum level. This may effectively stop the grafters 22 from reacting with the monomers 52, and thus no polymer chains could be formed or at least polymer chain growth is compromised. Accordingly, the premature termination of polymer chains, as well as the blockage of the reactive groups due to overly high grafter density may result in defective polymer, which will adversely affect the interfacial bonding strength between the polymer and the substrate. In other words, the provision and the interspersed arrangement of the diluters 32 in the composition 10 optimize the polymerization condition of the monomers 52 and the growing polymer chains 50, and consequently, significantly enhance the chemical and mechanical stability of the adhesion at the polymer and substrate interface.
In one embodiment, a preferred grafter density can be achieved by having the composition 10 comprise the first compound 20 and the second compound 30, and thus the grafters 22 and the diluters 32, in a volume ratio of at least about 1:1, and more preferably, in a volume ratio of above 1, i.e. with more grafters 22 than the diluters 32 in volume, but always with the presence of diluters 32.
Although the diluters 32 are required to be non-reactive to the monomers 52 and thus unable to initiate a polymerization reaction, it is possible for the diluters 32 to interact non-chemically with the polymer chains grafted at the grafters 22. The non-chemical interaction can be, for example, electrostatic attractions, hydrophobic interactions, etc. as long as the interactions do not interfere with the chemical reactions between the grafters 22 and the monomers 52, as well as with the propagation of the polymer chains 50.
In another embodiment, the one or more grafters 22 and the one or more diluters 32 of the first compound 20 and the second compound 30, respectively, may each comprise one or more reactive tail groups that are adapted to chemically bond among one another and with the surface functional groups of the substrate to thereby bond the first and the second compounds 20, 30 at the surface of the substrate 5. For example, the grafters 22 and the diluters 32 may each comprise one or more hydroxyl functional groups capable of reacting with one or more respective surface hydroxyl groups at the substrate 5 to form one or more chemical bonds to securely adhere the layer-like composition 10 on the substrate 5. Preferably, the diluters 32 are of a smaller molecular size than the grafters 22, for example, as illustrated in
In one further embodiment, both the grafters 22 and the diluters 32 are preferred to be hydrophobic in nature by, for example, comprising one or more hydrophobic organic linkers such as, but not limited to, alkyl or alkyl derivative groups which prevent water from permeating to and hydrolyzing the chemical bonds at the adhesion interface.
Although various examples of the compositions, the grafters and the diluters have been described, the present invention shall not be restricted or limited to these specific embodiments. Instead, a person skilled in the art would appreciate that any possible variations and/or modifications to the embodied structures, as long as they are considered functionally and chemically reasonable and applicable without departing from the inventive concept of the present invention, shall also be encompassed.
The present invention also relates to a substrate 5 having an intermediate layer 10 on a surface thereof for adhesion of a polymer such as, but not limited to Parylene. Said intermediate layer 10 comprising one or more first surface bonding units, such as the grafters 22, interspersed with one or more second surface bonding units, such as the diluters 32, wherein only the one or more first surface bonding units are capable of chemically reacting with one or more monomers 52 to form polymers 50 to thereby adhere the polymers 50 at the substrate surface. In one specific embodiment, the intermediate layer 10 is of a thickness of about 0.4 nm to about 0.8 nm. Preferably, the intermediate layer 10 is of a substantially monolayer-like structure.
Without being restricted to the application on the adhesion of Parylene, most commonly known polymers may actually be potentially applicable to the present invention. A number of possible examples, especially for polymer dialectic materials for electronic applications such as TSV insulation, may include: benzocyclobutene (BCB)-based polymers, epoxy-based polymers such as SU-8, polyimide, epoxy, and silicone. Parylene, being a poly(p-xylylene) polymer, is adopted as an example to demonstrate the efficacy of the present invention due to its availability in the market, relatively low costs and low processing temperature, as well as its good moisture blocking and dielectric insulating properties.
The present invention further relates to a method of preparing a polymer coated surface on a substrate using the composition 10. The method comprises the step of providing a solution having at least one first compound 20 and at least one second compound 30, with the at least one first compound 20 comprising one or more grafters 22, and the at least one second compound 30 comprising one or more diluters 32.
The solution is prepared by dissolving the at least one first compound 20 and the at least one second compound 30 in a solvent. In one embodiment, the solvent may comprise at least one of an alcohol and water. Preferably, the alcohol comprises isopropyl alcohol and the solvent is prepared by mixing isopropyl alcohol and water in about 1:1 volume ratio. In one preferred embodiment, the at least one first compound 20 is provided at a volume ratio of about 0.5%-about 1.0% in respect of a total volume of the solution; and that the at least one second compound 30 is provided at a volume ratio of about 0.2%-about 1.0% in respect of a total volume of the solution.
Specifically, after the solution is prepared, the surface to be coated will be immersed into said solution for about 10 min to about 30 min in ambient condition. After that the substrate will be removed from the solution, washed and be left for curing in ambient condition for over 8 hours to thereby allow the formation of a substantially layer-like coating of the composition 10 on the treated surface. As described earlier, the layer-like composition 10 comprises a plurality of grafters 22 and diluters 32 interspersingly arranged with one another, and more specifically, each of the grafters 22 and the diluters 32 comprises at least one reactive tail groups adapted to chemically bond among one another and with the surface functional groups of the substrate to thereby adhere the composition layer with the substrate.
The next step will be the reacting of the composition-coated surface with one or more monomers 52, such as p-xylylene, to thereby graft one or more Parylene polymers at the one or more grafter sites, but not at the one or more diluters 32. This reacting step can be conducted by any known polymerization or graft polymerization techniques, such as but not limited to, free radical chain-growth polymerization, for example, chemical vapor deposition (CVD) of Parylene. However, a person skilled in the art would understand that any other manner of polymerization technique such as but not limited to, bulk, solution, suspension, and/or emulsion polymerizations, and free radical chain-growth polymerization, ionic chain-growth polymerization, ring-opening polymerization and/or step-growth polymerization, may also be applicable.
To determine the adhesion strength provided by the composition 10, and particularly, whether the adhesion is sufficient to minimize, reduce or prevent interfacial delamination between the adhered Parylene layer and the substrate especially after the highly accelerated stress reliability test (HAST) conducted at 130° C., 85% relatively humidity and for 96 hours, a Tape Test is designed to quantify the degree of adhesion before and after the HAST. The steps of conducting the Tape Test are described as follows:
First of all, a sample substrate is treated under the HAST. After the HAST, the sample substrate adhered with a Parylene layer using the composition 10 in accordance with an embodiment of the present invention is marked by surface cutting the Parylene layer into an array of 10×10 squares, each having an area of about 1 mm2. The number of the undamaged film squares after the cutting are counted (i.e. the first count).
The surface of the Parylene array is attached with a piece of adhesive tape, followed by a manual pulling off of the tape from the Parylene layer. The number of any undamaged film squares in the array, i.e. squares of the undamaged Parylene layer, are counted again (i.e. the second count).
These taping, pulling, and counting steps are repeated up to 4 more times (i.e. the third to the sixth counts). Results of all the six counts are summed up to provide a score of XAH, as presented in the table of
A number of experiments with the respective Parylene layer being adhered to the substrate using different compositions 10 prepared under different grafter-to-diluter ratios—see the table of
It is confirmed by scanning electron microscopy (SEM) that samples with scores above 550 out of 600 demonstrate no interfacial delamination. The score of 550 is thus used as a benchmark in assessing any potential interfacial delaminations.
The Tape Test results as shown in the table of
The invention is advantageous in that it provides a composition for adhering a polymer to a substrate, and particularly, for providing and/or enhancing adhesions between a polymer and a substrate for electrical and electronic applications. For example, the composition of the present invention can be applied to adhere and/or to enhance adhesion of one or more insulating polymers, such as Parylene, with an electrically conducting surface such as, but not limited to, one or more silicon substrates of a through silicon via (TSV). The composition can be provided in the form of, for example, a layer-like structure adapted to chemically bond with a surface of the substrate. The composition comprises at least one first compound having one or more grafter units, with each of the grafters having at least one reactive functional head group adapted to chemically react with one or more monomers in forming the polymer. Particularly, the polymerization will result in one or more polymer molecules grafted at the respective grafter sites to thereby adhere the formed polymer chains at the substrate surface. More importantly, the composition also comprises at least one second compound having one or more diluter units, which are arranged to intersperse among the one or more grafters in the layer-like structure causing a reduction and thus, optimization of the grafter density at the layer-like structure. In contrast to the grafters, the diluters do not comprise reactive functional head groups for polymerization, and therefore, are not capable of chemically reacting with the monomers. No polymer chains can thus be grafted at the sites of the diluters. The invention is shown to allow optimization of the grafter density in the layer-like adhesive structure, and consequently, minimize, reduce or avoid chances of premature termination of the growing polymer chains. The invention is thus capable of significantly enhancing the interfacial bonding strength between the polymer and the substrate, and is found to be effective in minimizing, reducing, or avoiding interfacial delamination under the highly accelerated stress test (HAST).
The present description illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope.
Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only exemplary embodiments have been shown and described and do not limit the scope of the invention in any manner. It can be appreciated that any of the features described herein may be used with any embodiment. The illustrative embodiments are not exclusive of each other or of other embodiments not recited herein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims.
In the claims hereof, any element expressed as a means for performing a specified function is intended to encompass any way of performing that function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. It is thus regarded that any means that can provide those functionalities are equivalent to those shown herein.
In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.
