Patent Application
20230199972
The present invention relates generally to an oxide coating composition and a method of using the same to improve adhesion of metal surfaces, such as copper, to an inorganic material or polymeric resin material, in the manufacture of multilayer circuit boards.
A multilayer circuit board comprises, among other things, a number of metal layers circuit patterns, and a number of insulating layers there~between. These respective layers can have a wide variety of thickness. For example, they can be on the order of only microns thick, or much thicker.
In the typical fabrication of a multilayer circuit board, patterned circuitry innerlayers are first prepared by a process in which a copper foil-clad dielectric substrate material is patterned with resist in the positive image of the desired circuitry pattern, followed by etching away of the exposed copper. Upon removal of the resist, there remains the desired copper circuitry pattern.
One or more circuitry inner layers of any particular type or types of circuitry pattern, as well as circuitry innerlayers which might constitute ground planes and power planes, are assembled into a multilayer circuit by interposing one or more partially-cured dielectric substrate material layers (so-called “pre-preg” layers) between the circuitry innerlayers to form a composite of alternating circuitry innerlayers and dielectric substrate material. The composite is then subjected to heat and pressure to cure the partially-cured substrate material and achieve bonding of circuitry innerlayers thereto. The cured composite will then have a number of through-holes drilled therethrough, which are then metallized to provide a means for conductively interconnecting all circuitry layers. In the course of the through-hole metallizing process, desired circuitry patterns will typically be formed on the outer-facing layers of the multilayer composite.
An alternate approach to the formation of a multilayer printed circuit board is through additive or surface iarniner circuitry techniques. These techniques begin with a non-conductive substrate, upon which the circuit elements are additively plated. Further layers are achieved by repeatedly applying an imageable coating upon the circuitry and plating further circuit elements upon the imageable coating.
It has long been known that the strength of the adhesive bond formed between the copper metal of the circuitry inner layers and the cured pre-preg layers, or other non-conductive coatings, in contact therewith can be problematic, with the result that the cured multilayer composite or the coating is susceptible to delamination in subsequent processing and/or use. Based thereon, it is desirable to enhance the adhesion between the conducting and insulating layers to avoid delamination in subsequent manufacturing operations or in service. So called “black oxide” processes have been used for years to create a strongly adherent copper oxide layer to which an insulating layer would better adhere.
The assembled and cured multilayer circuit composite is provided with through-holes which require metallization in order to serve as a means for conductive interconnection of the circuitry layers of the circuit. The metallizing of the through-holes involves steps of resin desmearing of the hole surfaces, catalytic activation, electroless copper depositing, electrolytic copper depositing, and the like. Many of these process steps involve the use of media, such as acids, which are capable of dissolving the copper oxide adhesion promoter coating on the circuitry innerlayer portions exposed at or near the through hole. This localized dissolution of the copper oxide, which is evidenced by formation around the through-hole of a pink ring or halo (owing to the pink color of the underlying copper metal thereby exposed), can in turn lead to localized delamination in the multilayer circuit.
The art is well aware of this “pink ring” phenomenon and has expended extensive effort in seeking to arrive at a multilayer printed circuit fabrication process which is not susceptible to such localized delamination.
A major problem with the current use of oxide alternative compositions is the overall etch rate of the process. Etch rates in excess of 0.5-1.5 microns (20-60 microinches) generally create too much topography on the copper substrate. While this is advantageous for innerlayer bonding adhesion, it is unacceptable for the high-speed applications in the printed circuit board (PCB) market.
It has been found that traditional roughened copper surfaces create significant signal loss at these higher frequencies. Furthermore, with the move towards 5G technology, the market is in need of low-roughness innerlayer bonding applications.
Based thereon it is desirable to provide an improved low-roughness innerlayer bonding process that overcomes the deficiencies of the prior art.
The present invention relates generally to a nano oxide coating composition that exhibits low-roughness and promotes innerlayer bonding by creating a nano crystalline oxide structure on the copper surface.
Other low-roughness technologies that have been suggested include a tin process (a commercial product of which is available under the trade name FlatBond GT from Uyemura International Corporation), an organic coating ( a commercial product of which is available under the trade name GLiCAP from Shikoku Chemicals), and an oxide technology (a commercial product of which is available under the trade name NovaBond from Atotech).
However, these technologies have some deficiencies that it would be desirable to overcome. For example, the FlatBond GT product requires new, expensive equipment and the cost of tin is much higher than the oxide used in the instant invention. The GLiCAP product has been shown to exhibit poor adhesion after thermal process. Finally, the NovaBond oxide operates at a very high temperature and can only run in vertical applications. The NovaBond oxide process also requires additional process steps for the post dip application,
Thus, it would be desirable to develop an improved new process for improving adhesion of inorganic materials to metal surfaces that exhibits low-roughness that overcomes the deficiencies of the prior art.
It is an object of the present invention to provide an improved process for the adhesion of inorganic materials to metal surfaces.
It is another object of the present invention to provide a process for the adhesion of inorganic materials that does not require a post dip step to ensure acid resistance.
It is another object of the present invention to provide a process that improves adhesion without etching the surface of the metal substrate.
It is still another object of the present invention to provide a process of promoting innerlayer bonding without etching the copper substrate,
It is yet another object of the present invention to provide a process of promoting innerlayer bonding by creating a nano crystalline oxide structure on a copper substrate.
It is still another object of the present invention to provide an improved adhesion promoting process that can be installed in existing equipment.
It is still another object of the present invention to provide an improved adhesion promoting process that can be used at a lower operating temperature.
To that end, in one embodiment, the present invention generally relates to a process for enhancing adhesion between a metal conducting layer and an inorganic material or polymeric resin material during manufacture of a multilayer circuit board, the process comprising the steps of:
The present invention will now be described with reference to the following figures, in which:
The present invention relates generally to a process for improving the adhesion of inorganic materials and polymeric resin materials to a metal surface, especially copper or copper alloy surfaces. The process proposed herein is particularly useful in the production of multilayer printed circuits. The process proposed herein provides optimum adhesion between metallic and polymeric surfaces (i.e., the circuitry and the intermediate insulating layer), and eliminates and/or substantially minimizes pink ring.
The inventors of the present invention have discovered a nano-oxide process that exhibits low-roughness and does not require a post dip step to ensure acid resistance. The novel one-step oxide bath described herein also allows the process to be installed into existing oxide alternative equipment.
This novel nano oxide process does not require a post dip step to ensure acid resistance (i.e., elimination and/or minimization of “pink ring”). The one-step bath allows for the chemistry to be installed into existing oxide alternative equipment, including horizontal equipment. In addition, the lower operating temperature afforded by the process allows the one-step bath to be implemented into existing equipment.
As used herein, “a,” “an,” and “the” refer to both singular and plural referents unless the context clearly dictates otherwise.
As used herein, the term “about” refers to a measurable value such as a parameter, an amount, a temporal duration, and the like and is meant to include variations of +/-15% or less, preferably variations of +/- 10% or less, more preferably variations of +/- 5% or less, even more preferably variations of +/-1% or less, and still more preferably variations of +/-0.1% or less of and from the particularly recited value, in so far as such variations are appropriate to perform in the invention described herein. Furthermore, it is also to be understood that the value to which the modifier “about” refers is itself specifically disclosed herein.
As used herein, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, are used for ease of description to describe one element or feature’s relationship to another element(s) of feature(s) as illustrated in the figures. It is further understood that the terms “front” and “back” are not intended to be limiting and are intended to be interchangeable where appropriate.
As used herein, the terms “comprises” and/or “comprising,” specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
As used herein, the term “substantially free” or “essentially free” if not otherwise defined herein for a particular element or compound means that a given element or compound is not detectable by ordinary analytical means that are well known to those skilled in the art of metal plating for bath analysis. Such methods typically include atomic absorption spectrometry, titration, UV-V is analysis, secondary ion mass spectrometry, and other commonly available analytically techniques.
All amounts are percent by weight unless otherwise noted. All numerical ranges are inclusive and combinable in any order except where it is logical that such numerical ranges are constrained to add up to 100%,
The terms “composition” and “bath” and “solution” are used interchangeably throughout this specification.
The term “alkyl,” unless otherwise described in the specification as having substituent groups, means an organic chemical group composed of only carbon and hydrogen and having a general formula: CnH2n+1.
The term “average” is equivalent to the mean value of a sample.
In one embodiment, the present invention generally relates to a process for enhancing adhesion between a metal conducting layer and an inorganic material or polymeric resin material, the process comprising the steps of:
In one embodiment, the metal conducting layer comprises copper or a copper alloy.
The method described herein is capable of treating smooth copper surfaces to produce a nano oxide crystalline oxide structure thereon without having any measurable effect on surface roughness. The nano oxide crystalline oxide structure of the treated copper surface exhibits excellent adhesion and thermal resistance when used with various inorganic materials and polymeric resin materials, including pre-preg materials. These inorganic materials include, for example, silicons, ceramics, inorganic materials used as fillers, and glass.
Examples of the polymeric resin materials include: an acrylate resin, an epoxy resin, a polyimide resin, a bismaleimide resin, a maleimide resin, a cyanate resin, a polyphenylene ether resin, a polyphenylene oxide resin, an olefin resin, a fluorine-containing resin, a polyetherimide resin, a polyether ether ketone resin, and a liquid crystal resin, and may be a combination thereof by mixing or modifying with each other.
Exemplary polymeric resin materials include multifunctional resin systems, including those that are designed for multilayer printed wiring board applications that require high thermal performance and reliability. Examples of these resin systems include, for example, an 370HR epoxy laminate available from Isola, Megtron Series dielectric circuit board materials available from Panasonic, Inc. (including, for example, Megtron M, Megtron 2, Megtron 4, Megtron 6, Megtron 7, and Megtron 7N), 6 and Megtron 7N, and microfilms such as Ajinomoto Build-up Film (ABF), available from Ajinomoto Group.
In one embodiment, the copper surface is treated to pre-clean the copper surface prior to contact with the oxide coating composition. One suitable pre-cleaner is an acid precleaner, commercial products of which are available under the tradenames 717 Acid Cleaner, MultiBond Acid Cleaner S and M-Speed Clean from MacDermid Enthone, Inc.
Thereafter, the copper surface is subjected to a pre-dip step. The pre-dip composition is generally selected to be compatible with the oxide coating composition. In one embodiment, the pre-dip composition comprises the same alkali and acid as the adhesion promoting composition, without the organic component (i.e., corrosion inhibitor) or the oxidizing agent. The main function of the pre-dip is to seed the copper surface with a thin layer of oxide so that the main oxide coating bath can initiate oxide uniformly and more quickly. In one embodiment, the pre-dip is performed using a different concentration of the oxide coating composition described herein.
In one embodiment, the metal conducting layer is contacted with the pre-dip composition for a period of about 10 to about 240 seconds, more preferably about 30 to about 45 seconds, and is thereafter contacted with the oxide coating composition for a period of about 10 to about 240 seconds, more preferably about 30 to about 90 second, more preferably about 45 to about 60 seconds to produce the nano oxide crystalline oxide structure on the surface of the metal conducting layer.
Contact with the oxide coating composition may be by any conventional means, including immersion in a bath of the oxide coating composition or other means of contact for the period of time.
In an alternate embodiment, the process described herein does not require a pre-dip step prior to the adhesion promoting step. That is, the metal conducting layer is contacted directly with the oxide coating composition without first contacting the metal conducting layer with a pre-dip composition.
It has been found that the improved process of the invention results in no increased topography of the copper surface substrate, improves cosmetic appearance, and improves thermal and chemical resistance to post lamination processes. The method can be incorporated in printed circuit board manufacturing processes to improve bonding between innerlayers used in high frequency applications while maintaining excellent signal integrity.
The process described herein can be used in both, horizontal and vertical process configurations. One skilled in the art would know that horizontal and vertical process configurations may require different times or temperatures to achieve the same desired result. In one embodiment, the process described herein can be used in existing horizontal equipment that is configured for use with oxide alternative chemistry and the composition described herein replaces such oxide alternative chemistry. In another embodiment, the process described herein is used in a vertical configuration.
The alkali usable in the oxide coating composition may be a hydroxide, including, for example, sodium hydroxide, potassium hydroxide, or ammonium hydroxide, In one embodiment, the alkali comprises sodium hydroxide. The alkali is typically used in an amount. sufficient to maintain the pH of the composition within the desired range. In a preferred embodiment, the concentration of the alkali in the coating composition is in a range of about 1 to 50 g/L, more preferably about 5 to about 20 g/L,
The oxidizing agent is chosen for its stability in the composition and is preferably sodium chlorite. The inventors have found that sodium chlorite provides a good result due to its stability, while other oxidizing agents such as chloryls, perchloryls, hypochlorites, chlorates, and perchlorates are generally not preferred because they are not stable in the composition. The oxidizing agent is preferably used at a concentration within a range of about 10 to about 240 g/L, more preferably within a range of about 70 to 180 g/L, most preferably within a range of about 140 to 150 g/L.
The acid used in the composition described herein is typically an inorganic acid. In a preferred embodiment, the acid comprises phosphoric acid due to its grain refining capability. preferred embodiment, the acid comprises phosphotic acid due to its grain refining capability. The concentration of the acid in the composition is preferably within a range of about 1 to about 20 g/L, more preferably about 2 to about 10 g/L, and most preferably about 2.5 to about 5.0 g/L.
The corrosion inhibitor is preferably a nitrogen heterocyclic compound. In one embodiment, the nitrogen heterocyclic compound is a 5 and 6 membered nitrogen heterocyclic compound which may be selected from azoles, pyridines, pyrimidines, piperidines, and morpholines. In one embodiment, the nitrogen heterocyclic compound is incorporated in the formulation to form an acid resistant coating on the metal conducting layer and reduce and/or eliminate pink ring. This nitrogen heterocyclic compound is incorporated into the plating composition in an amount sufficient to bond with the oxide coating to produce an acid resistant surface on the metal conducting layer.
While many nitrogen heterocyclic compounds attribute some sort, of acid resistance to the metal conducting layer, preferred compounds also result in a good cosmetic appearance and are compatible with the other ingredients of the composition. By “good cosmetic appearance” what is meant is a surface that is uniform in color, with no blotchy spots or discoloration.
The inventors have found better success with smaller inhibitors with respect to acid resistance due in part to their ability to coordinate more readily with the oxide structure. Based thereon, in one embodiment, the corrosion inhibitor is an unsubstituted or substituted azole.
In one embodiment, the nitrogen heterocyclic compound is unsubstituted or substituted with a halogen substituent, where efficacy is generally inversely proportional to the molecular weight of the halogen substituent.
Examples of preferred azole-based inhibitors include substituted or unsubstituted pyrazoles, imidazoles, triazoles, tetrazoles, thiazoles, carbazoles, indazoles, benzimidazoles, benzotriazoles, benzothiazoles, benzoduadiazoies, and combinations of one or more of the foregoing. In one embodiment, the azole-based inhibitor has a ring structure that includes a halogen substituent, which halogen substituent may be, for example, chloride or bromide. In another embodiment, the azole-based inhibitor is a sulfur substituted azole-based inhibitor, such as a sulfur substituted benzotriazole.
Examples of suitable azole based inhibitors usable in the compositions of the invention include, but are not limited to, imidazole, 14-dichlobenzotriazole, 4,5-dichioro-2H-benzotriazole, 1,4-dichlorobenzotriazole, 5,5-dichlorobenzotriazole, 5 6-dichlorobenzotriazole, 2,5-dichlorobenzotriazole, 2,4-dichlorobenzotriazo!e, 2,6-dichlorobenzotriazole, 2,7-dichlorobenzotriazole, 5-chlorobenzotriazole, 1-chlorobenzotriazole, 2-chlorobenzotriazole, 2bromo-1H-indazole, 4-bromo-1H-indazole, 5-bromo-1H-indazole, 6-bromo-1H-indazoIe, 7-bromo-1H- indazole, 4-bromo-1H-imidazole,5-bromo-1H-imidazole-2-carboxylic acid, 1,2-dibronroimidazole-d-carboxylic acid, 2,4-dibromo-1H-imidazole, 4,5-dibromo-1H-imidazole, 1,4-dibromo- 1H-imidazole, 4,4-dibromo- 1H-imidazole, benzimidazole, 2-4-dibromoimidazole, 4,5-dichloroimidazole, 1,5-dichloromidazole, 3,4-dichloroimidazole, 4,5-dichloroimidazole-1-carboxylic acid, 1 ,2-dicloroimidazole, 4,5-dicbloro- 1H-imidazole, 2,2-dichloroimidazole, 1,4-dichloroimidazole, 4,4-dichloroimidazole, 2,5-dichloro-1H-imidazole, benzotriazole-5-carboxlicy acid, and other similar compounds, along with combinations of one or more of the foregoing,
While the use of azole-based corrosion inhibitors in adhesion promoting compositions of the prior art, is described, for example, in U.S. Pat. Nos. 6,554,948, 6,419,784, and 6,146,701, all to Ferrier, these prior art compositions are designed to produce a microroughened surface. In contrast to prior art compositions that are based on azole chemistry, the compositions of the present invention are designed not to provide any micro-roughening but rather to produce a nano oxide layer on the surface of the metal conducting layer that exhibits a good cosmetic appearance. As such, the particular type of corrosion inhibitor and the concentration(s) at which the corrosion inhibitors are used, along with concentrations of the other bath constituents, are important aspects of the present invention.
The inventors have discovered that a critical aspect of the present invention is the size of the nitrogen heterocyclic compound. It has surprisingly been found that smaller organic structures can produce a greater peel strength per unit surface area and coordinate better with the formation of the oxide on the surface of the metal conducting layer. Thus, as set forth herein, monocyclic compounds are generally preferred. On the other hand, as the structure of the nitrogen heterocyclic compound grows in size, efficacy can be reduced.
The nitrogen heterocyclic compounds described herein are typically used at a concentration within a range of about 1 ppb to about. 5,000 ppm, depending on the particular inhibitor, and substituents attached to the ring structure, and the molecular weight of the nitrogen heterocyclic compound as well as the type and concentrations of the other bath constituents.
The difference in concentration range employed can be attributed to the electron donating or withdrawing properties of the substituents. As with electronic-donating chloride substitution, it increases the strength of the nitrogen bond to the copper surface, thereby making the inhibitor strong. Whereas the electron withdrawing carboxylic acid group weakens the inhibitor leading to the use of higher concentrations. In the case of sulfur substitution, sulfur can act as a nucleophile and lead to very strong inhibition.
For example, benxotriazoles, including chlorobenzotriazoles, may be used at a concentration in the range of about 25 to 300 ppm, more preferably 50 to 150 ppm, most preferably 70 to 80 ppm. On the other hand, benzotriazole-5-carboxylic acid may be used at a concentration in the range of about 100 to 2,000 ppm, more preferably 500 to 1,500 ppm, most preferably about 900 to about 1,100 ppm, and sulfur substituted benzotriazoles, may suitably be used at concentrations as low as 1 ppb, such as concentrations between 1 and 50 ppb.
In one embodiment, the oxide coating composition comprises:
In a preferred embodiment, no other components are included in the composition described herein. In one embodiment, the present invention consists essentially of an alkali, an oxidizing agent, an acid, and the nitrogen heterocyclic compound at concentrations as described herein. In another embodiment, the present invention consists of an alkali, an oxidizing agent, an acid, and the nitrogen heterocyclic compound , absent any unavoidable contaminants at concentrations as set forth herein. By “consisting essentially of”, what is meant is that the composition is free of any component that has a detrimental effect on oxide weight, adhesion promoting, edge attack, and acid resistance.
The inventors of the present invention have found that the ratio of oxidizing agent to alkali has an effect on the oxide structure, oxide color, etc. and can ultimately change the performance of the oxide. In one embodiment, the ratio of chlorite to sodium hydroxide in the composition, is within a range of about 1:1 to about 20:1, more preferably about 10:1 to about 19:1, most preferably about 15:1 to about 18:1.
The pH of the oxide coating composition is preferably maintained over the Lifetime of the oxide coating composition at between about 11 to about 15, more preferably about 12 to about 14, more preferably about 12.5 to about 13.8, most preferably at about 13.1 to about 13.3. In one embodiment, the pH of the oxide coating composition is maintained at about 13.2 over the lifetime of the oxide coating composition. If adjustments are necessary,alkali and/or acid can be added to adjust the pH of the composition to within the desired range.
The temperature of the oxide coating composition is preferably maintained at between about 40 and 80° C., more preferably between about 45 and 75° C., most preferably between about 48 and about 60° C. In one embodiment, the temperature of the oxide coating composition is maintained at about 50° C. for both the pre-dip and the coating solution. The temperature of the oxide coating composition can be maintained at this level during both horizontal and vertical processing. In addition, it is believed that a temperature within this range is optimal for horizontal processing.
After contacting the copper surface with the oxide coating composition to create the nano-crystalline oxide structure on the copper surface, a dielectric non-conductive layer, such as a pre-preg layer, polymeric photoresist, dry film, etc., is placed directly adjacent, to the copper surface in an adhesion step to join the copper surface to the dielectric non-conductive layer and form a multi-layer printed circuit board. Heat and/or pressure can be used to initiate the adhesion reaction. Several layers may be placed together in the adhesion step to laminate several layers together in a single step.
Oxide weight is one indicator of bath performance and is evaluated by copper weight gain coupons. It is desirable that the oxide weight be high enough to promote excellent adhesion while at the same time being low enough to provide sufficient acid resistance. The oxide weight is preferably between about 0.010 and about 0.150 mg/cm2. more preferably about 0.015 to about 0.035 mg/cm2. Below an oxide weight of about 0.025 mg/cm2, it is observed that acid resistance is better, while above an oxide rate of about 0.040 mg/cm2, it is observed that the acid attack is more prevalent.
The invention will now be described with reference to the following non-limiting examples:
The cycle set forth in Table 1 was used in processing copper foils to manufacture 6-jayet test panels (Megtron-6 Pre-preg, available from Panasonic) for all of these examples:
MultiBond Acid Cleaner S and MultiBond Alkaline Cleaner R are both available from MacDermid Enthone Inc., Waterbury, CT.
It is noted that all of the examples were processed vertically according to the steps of Table 1.
The following parameters were evaluated:
Tests were conducted to evaluate the effectiveness of various oxide coating compositions.
An oxide coating composition was prepared comprising:
Aqueous solutions were made up by mixing the alkali, oxidizing agent, and acid together along with the listed corrosion inhibitors to produce Solutions 1 to 4. Each of Solutions 1 to 4 was then applied to the copper foils to manufacture the 6-layer test panel.
The test foils were contacted with the aqueous solutions for a 30/60 second cycle, in which the first number refers to the dwell time in the pre-dip composition and the second number refers to the dwell time in the oxide coating composition. Thereafter, the test panels were examined.
Table 2 shows the results of pink ring (µm) after steps of Desmear, plated through-hole processing (PTH), and acid copper and edge attack (µm) after Desmear and PTH. As seen in Table 2, the compositions containing the corrosion inhibitor of the invention resulted in much smaller amounts of both pink ring and edge attack, indicating that better acid resistance was achieved.
A time study was performed to compare a test solution that did not contain a corrosion inhibitor and a solution that contained 75 ppm of Benzotriazole as a corrosion inhibitor and the results are shown in Table 3. Both oxide weight and peel strength were measured for different dwell times in the test solutions. As shown in Table 3, the oxide weight at a dwell time of 30/60 seconds was much lower in the solution that contained the corrosion inhibitor and within the desired oxide weight. As set forth above, the first number refers to the dwell time in the pre-dip composition and the second number refers to the dwell time in the oxide composition.
As seen in Table 3, the oxide weight at higher dwell times was much higher, indicating that lower dwell times provided a better result. In addition, peel strength was determined both as is and after 6X reflows. The peel strength is better without the organic corrosion inhibitor, both as is and after 6X reflows. With the corrosion inhibitor in the oxide bath, it coordinates with the oxide during formation of the nano coating and slightly modifies the structure yielding slightly lower adhesion but improved acid resistance
The same study was performed using 75 ppm of 5-Chlorobenzotriazole and the results are shown in Table 4. Both oxide weight and peel strength were measured for different dwell times in the test solutions. As shown in Table 4, the oxide weight at a dwell time of 30/60 seconds was much lower in the solution that contained the corrosion inhibitor and within the desired oxide weight. However, the oxide weight at higher dwell times was much higher, indicating that lower dwell times provided a better result. In addition, peel strength was observed both as is and after 6X reflows.
The same study was also performed using 1,000 ppm of Benzotriazole-5-carboxylic acid and the results are shown in Table 5. Both oxide weight and peel strength were measured for different dwell times in the test solutions. As shown in Table 5, the oxide weight at a dwell time of 30/60 and 60/120 seconds was much lower in the solution that contained the corrosion inhibitor and within the desired oxide weight. However, the oxide weight at higher dwell times was much higher, indicating that lower dwell times provided a better result. In addition, peel strength was observed both as is and after 6X reflows.
A time study was performed to determine the amount of edge attack for several different azoles, at various dwell times. The copper foils were processed through the nano oxide process and then laminated with the desired resin system. After lamination, one-inch strips were taped off and the remaining copper was etched away to expose the laminate. The test samples were then processed through Desmear and PTH and then the taped strips were pulled from the laminate. The edges of the strips were viewed under a high magnification microscope to determine the amount of attack on the oxide coating. The results are shown in Table 6.
A desirable edge attack value is preferably less than about 100 µm, more preferably less than about 50 µm, more preferably less than about 40 µm, more preferably less than about 30 µm, more preferably less than about 20 µm, and even more preferably less than about 15 µm.
A time study was performed to compare a test solution that did not contain a corrosion inhibitor as compared with a solution that contained 75 ppm of Benzotri azole as a corrosion inhibitor as described above in Table 3 but for different dwell times and the results are shown in Table 7. Both oxide weight and peel strength were measured for different dwell times in the test solutions. As shown in Table 7, the oxide weight at dwell times of 30/60 seconds and lower were all much lower in the solution that contained the corrosion inhibitor and within the desired oxide weight.
Table 8 depicts a time study of edge attack data for dwell times of 15/30 to 120/240 for the benzotriazole corrosion inhibitor. As shown in Table 8, the edge attack was less at all dwell times as compared with the solutions that did not contain an organic and the values of edge attack were generally better at lower dwell times.
Table 9 depicts a time study of oxide weight and adhesion (peel strength) for dwell times of 15/30 to 30/60 for the benzotriazole corrosion inhibitor.
The dwell time study shows that higher oxide weight and thickness leads to more acid attack at the interface. The shorter dwell times (i.e., less than 30/60 seconds) exhibited better acid resistance and edge attack as low as 14 µm.
The BTA concentration was adjusted to optimize peel strength and cosmetic uniformity. In one embodiment, a BTA concentration of 75 ppm was determined to produce a good result.
The present invention shows that for various nitrogen heterocyclic compounds , a dwell time of 30/60 seconds provides a good result.
A study was performed using Imidazole as the corrosion inhibitor and the results are provided below in Table 10 for various concentrations of imidazole.
As shown in
A study was performed using Dichlorobenzotriazole as the corrosion inhibitor and the results are provided below in Table 11,
As shown in
As set forth in Table 12, the 4-Bromo-1H-indazole was used at a much lower concentration than the other azoles described above. However, at concentrations in the range of 2-6 ppm,oxide weight, edge attack and peel strength values demonstrated good results, although, oxide weight and peel strength decreased at the higher concentration of 6 ppm. However, edge attack values were higher than for some of the other azole corrosion inhibitors tested.
As seen in Table 13, the bath was most stable at only lower concentrations of benzimidazole. While oxide rate remained acceptable, the peel strength did not demonstrate good results above about 25 ppm and edge attack values were high throughout the range. Thus, while Benzimidazole may be used as the azole corrosion inhibitor, careful control of the benzimidazole concentration and other parameters is necessary to produce an acceptable result.
As seen in Table 14, the bath shuts down at a concentration of 400 ppm imidazole. The peel strength at this concentration was less than 0.5 lbs./in, due to very low oxide weight and poor oxide development. However, edge attack values were very good over the concentration range.
As set forth in Table 15, the bath did not shut down up to 150 ppm 4~Bromoirnidazole. There was a gradual decrease in oxide weight, but excellent peel strength was maintained. Edge attack performance held steady and was acceptable but not great.
A further study of 4-Bromo-imidazole was performed over a wider concentration range and the results are shown in Table 16.
As seen in Table 16, the bath did not shut down, even at concentrations of 400 ppm 4∼ Bromo-imidazole. There was a continued decrease in oxide weight as the concentration increased, but the peel strength remained excellent. There was a significant improvment in edge concentrations, but it was observed that the cosmetic appearance exhibited a little non-uniformity. attack at the higher little non-uniformity.
As seen in Table 17, the bath did not shut down, even at 500 ppm. No significant changes in performance were observed in terms of oxide weight gain, cosmetics, edge attack, and peel strength over the concentration range. However, the edge attack performance was relatively poor over the concentration range.
As seen in Table 18 the bath did not shut down even at a concentration of 800 ppm. However, the cosmetic appearance at this concentration was unacceptable and the oxide weight and peel strength dropped off significantly. Throughout the concentration range up to 400 ppm, the oxide weight and peel strength remained steady. The edge attack performance was poor as compared with other azoles.
The examples demonstrate that the type and concentration of the nitrogen heterocyclic compounds along with the dwell times are important factors for enhancing adhesion between metal conducting layers and inorganic materials using the process described herein and that a balance of these factors is necessary to achieve optimal results.
It is desirable that the nitrogen heterocyclic compound be used in the bath at a concentration that is capable of achieving the following desirable properties:
For the best results, it is preferred that all of these properties be met. As evidenced by the examples, the concentration of the nitrogen heterocyclic compound in the composition can vary widely depending on the particular inhibitor being used.
Finally, it should also be understood that the following claims are intended to cover all of the generic and specific features of the invention described herein and all statements of the scope of the invention that, as a matter of language might fall therebetween.
