1. Field of the Invention
This invention relates to materials and methods of drilling printed circuit boards.
2. Description of the Related Art
The use of printed circuit boards in the electronics industry has grown rapidly over the past several decades. In order for the printed circuit boards to be utilized, the boards must undergo a drilling process whereby multiple thru-holes and blind holes are drilled into each board. Generally, multiple boards having one or more layers of copper and/or prepeg are stacked on top of each other and drilled simultaneously. During this process the boards may become damaged due to one or more of the following: burring, contact with the pressure foot, and excessive heat from the drill bit. Backup and entry boards have been used to help improve this drilling process. Backup boards are generally a hard board that is placed at the bottom of the stack of printed circuit boards. Entry boards are generally placed at the top of and/or interspersed throughout the stack of printed circuit boards.
In one embodiment, this invention relates to methods and materials for use in printed circuit board drilling applications. In one embodiment, there is provided a drilling process in which one or more printed circuit boards are stacked on top of a preferred backup board and drilled. In another embodiment, there is provided a drilling process in which an entry board is placed on top of one or more printed circuit boards which are then drilled. In other embodiments, a combination of backup and entry boards are used in the drilling process. In preferred embodiments backup boards comprising a core material, a lubricant, and an outer shell material are used. Preferably the lubricant is a substantially separate and distinct layer. In other preferred embodiments entry boards comprising a substantially separate and distinct lubricant layer and an outer shell material are used. Preferably the lubricant is a substantially separate and distinct layer.
In one embodiment, a preferred backup board comprises a first outer shell layer, one or more lubricant layers, a core material layer, one or more lubricant layers, and a second outer shell layer, wherein the layers are in the order recited. In another embodiment, the one or more lubricant layers are preferably substantially separate and distinct layers. In one embodiment, the one or more lubricant layers comprise polyethylene glycol and/or polyalkylene oxide compounds. In certain embodiments wherein more than one lubricant layer is present, the lubricants may be the same type and/or form or they may differ. In one embodiment a resistance sheet is used to provide support for one or more of the one or more lubricant layers. In other embodiments, the outer shell materials may be the same or they may differ. In one embodiment, the layers of preferred backup boards are secured together using an adhesive.
In one embodiment, a preferred entry board comprises a first outer shell layer, one or more lubricant layers, and a second outer shell layer, wherein the layers are in the order recited. In one embodiment, the one or more lubricant layers are preferably substantially separate and distinct layers. In one embodiment, the one or more lubricant layers comprise polyethylene glycol and/or polyalkylene oxide compounds. In certain embodiments wherein more than one lubricant layer is present, the lubricants may be the same type and/or form or they may differ. In one embodiment a resistance sheet is used to provide support for one or more of the one or more substantially separate and distinct lubricant layers. In other embodiments, the outer shell materials may be the same or they may differ. In one embodiment, the layers of preferred entry boards are secured together using an adhesive.
The layers of preferred backup and entry boards may be secured together using one or more of the following: adhesive, tabs, pins, straps, shrink wrap, tape, and other suitable securing devices. In a preferred embodiment, an adhesive is used. Suitable adhesives include, but are not limited to, epoxy, phenolic adhesive, urethane adhesive, and urea formaldehyde. In preferred embodiments utilizing an adhesive, the adhesive may cover the entire layer or only a portion of the layer.
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All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present inventions will become readily apparent to those skilled in the art from the following detailed description of preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.
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Figures are generally schematic in nature and are not to scale.
In one embodiment, this invention relates to methods and materials for use in printed circuit board drilling applications. In one embodiment, there is provided a drilling process in which one or more printed circuit boards are stacked on top of a backup board according to embodiments disclosed herein, and drilled. In another embodiment, the drilling process includes the use of an entry board which is placed on top of the printed circuit boards to be drilled. Alternatively, the entry board may also be used in one or more places within the stack of printed circuit boards to be drilled. In another embodiment, the drilling process includes the use of both entry and backup boards. In preferred embodiments, backup boards comprising a core material, a lubricant, and an outer shell material are used. In preferred embodiments, entry boards comprise a lubricant and an outer shell material. Preferably the lubricant layers of preferred backup and entry boards are substantially distinct layers. In one embodiment, the layers of preferred backup and entry boards are secured together using an adhesive.
As used herein, the term “backup board” is a broad term used in its ordinary sense and includes, without limitation, boards placed on the bottom of a printed circuit board stack during drilling applications. As used herein, the term “entry board” is a broad term used in its ordinary sense and includes, without limitation, boards placed on the top, bottom, and/or within a stack of printed circuit boards during drilling applications. In preferred embodiments, entry boards comprise a lubricant and an outer shell material. In other embodiments, an entry board may further comprise a core. Preferably the lubricant layers are substantially distinct layers. In one embodiment, the layers of preferred entry boards are secured together using an adhesive. As used herein, the terms “drilling” and “drilling applications” are broad terms used in their ordinary sense and include, without limitation, a process of forming holes or channels in printed circuit boards.
Preferably drilling applications utilizing preferred backup and/or entry boards demonstrate one or more of the following characteristics: improved thru-hole or blind hole (decreased roughness, and decreased nailheading) quality, substantially no burring, improved drill accuracy, prolonged drill life, decreased drilling temperature, improved ability to increase amount of printed circuit boards drilled at once, and improved ability to drill through printed circuit boards that are typically becoming more difficult to drill through due to increased thicknesses of the boards and/or more abrasive circuit board components containing higher Tg materials (e.g. Polyimide resin, ceramic, ceramic-filled PTFE, Getek®).
In one preferred embodiment backup boards comprising a core, a lubricant as a substantially separate and distinct layer on each side of the core, and an outer shell material on each side of the substantially separate and distinct lubricant layer are used. See, for example,
In another preferred embodiment backup boards comprising a core, a lubricant as a substantially separate and distinct layer on each side of the core, and an outer shell on each side of the substantially separate and distinct lubricant layers may be bonded together by a substantially separate and distinct adhesive layer while maintaining the lubricant as a substantially separate and distinct layer in and of itself. See, for example,
In other preferred embodiments entry boards comprising a core, a lubricant as a substantially separate and distinct layer on each side of the core and an outer shell on each side of the lubricant layer are used. See, for example,
In other preferred embodiments entry boards comprising a core, a lubricant as a substantially separate and distinct layer on each side of the core, and an outer shell on each side of the substantially separate and distinct lubricant layers may be bonded together by a substantially separate and distinct adhesive layer while maintaining the lubricant as a separate and distinct layer in and of itself. See, for example,
In other preferred embodiments entry boards comprising a lubricant as a substantially separate and distinct layer and outer shells on each side of the substantially separate and distinct lubricant layer are used. See, for example,
In other preferred embodiments entry boards comprising a lubricant as a substantially separate and distinct layer and outer shells on each side of the substantially separate and distinct lubricant layer may be bonded together by a substantially separate and distinct adhesive layer while maintaining the lubricant as a substantially separate and distinct layer in and of itself. See, for example,
In a preferred embodiment, a backup board comprises a core material, a lubricant, and an outer shell material. In another preferred embodiment, an entry board comprises an outer shell material and a lubricant. In one embodiment, an entry board further comprises a core. Preferably the lubricant layers are substantially separate and distinct layers. In one embodiment, the layers of preferred backup and entry boards are secured together using an adhesive. Preferably the adhesive layers are substantially separate and distinct layers.
As presently contemplated, suitable core materials include, but are not limited to, high-density fiberboard (HDF), medium density fiberboard (MDF), metal (e.g. aluminum or copper), metal alloys, paper, melamine, random fiber mats, plastic, chip board, particle board, phenolic alone or supported with paper, cloth, glass fiber and the like (e.g. phenolic similar to prepeg used in circuit boards), solid or laminated phenolic sheets, and the like. In one embodiment, core thickness preferably ranges from about 0.0001 inches to about 0.125 inches, but also including about 0.0005, 0.001, 0.005, 0.01, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.10, 0.105, 0.110, 0.115, and 0.12 inches and ranges encompassing these amounts. In one preferred embodiment, the core thickness is from about 0.085 inches to about 0.095 inches, preferably from about 0.087 inches to about 0.088 inches.
As presently contemplated, suitable lubricants include, but are not limited to, polyethylene glycol, polypropylene glycol, and/or polyalkylene oxide compounds, preferably polyethylene oxide, polypropylene oxide, and combinations thereof. In one embodiment, suitable lubricants include, but are not limited to, those in the form of an extruded lubricant layer, a hot melt coating lubricant layer or cast hot melt lubricant layer, or as a lubricant saturated paper layer. One such suitable lubricant is a water-soluble polyethylene glycol based lubricant. For example, a suitable lubricant includes, but is not limited to, a polyalkylene oxide compound obtained by addition polymerizing alkylene oxide mainly composed of ethylene oxide into an organic compound having two active hydrogen group. Other suitable lubricants are described U.S. Pat. No. 5,507,603 to Nakano et al.
In one embodiment, lubricant thickness preferably ranges from about 0.0001 inches to about 0.03 inches, but also including about 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.015, 0.02, and 0.025 inches and ranges encompassing these amounts. In another embodiment, lubricant thickness preferably ranges from about 0.0001 inches to about 0.125 inches, but also including about 0.0005, 0.001, 0.005, 0.01, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.10, 0.105, 0.110, 0.115, and 0.12 inches and ranges encompassing these amounts. In a preferred embodiment, the lubricant thickness is about 0.003 inches. Preferred lubricants preferably demonstrate one or more of the following characteristics depending on the application: the lubricant hardens when cooled, the lubricant liquefies when heated, is water soluble, is chemically soluble, provides lubrication at desired drilling temperature, lubricant deposits on the hole wall are readily removable (e.g. removable with high pressure wash), does not interfere with post-drilling processes, is easy to handle, is stable (e.g. does not substantially degrade during the life of the product), adds additional rigidity to the board.
As presently contemplated, suitable outer shell materials include, but are not limited to, aluminum, aluminum alloys, non-aluminum metals (e.g. copper), non-aluminum metal alloys, resin, film, resin film, melamine, phenolic (e.g. medium density overlay glue film), UV cured film, plastic, acrylic, polyurethane alone, polyurethane supported on paper, resin impregnated paper, and coated or uncoated paper. Preferably, although not required, suitable outer shell materials will provide added rigidity to the backup board. In one embodiment, outer shell thickness preferably ranges from about 0.0001 inches to about 0.03 inches, but also including about 0.0005, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.015, 0.02, and 0.025 inches and ranges encompassing these amounts. For example, in one embodiment a preferred outer shell is aluminum alloy 3003 H19 ranging in thickness from about 0.001 to about 0.002 inches thick, but also including about 0.00125, 0.0015, 0.00175 inches and ranges encompassing these amounts. In another embodiment, outer shell thickness preferably ranges from about 0.0001 inches to about 0.125 inches, but also including about 0.005, 0.01, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.10, 0.105, 0.110, 0.115, and 0.12 inches and ranges encompassing these amounts. In another embodiment, a preferred outer shell is a phenolic paper. For example, in one embodiment a phenolic glue film is used.
Other embodiments may include outer shell materials comprising paper coated with adhesive, plastic, melamine, ultra violet (UV) curable film, or resin coatings. In one embodiment the adhesive is an epoxy. In one embodiment, paper is coated with a UV cured epoxy coating. For example, a cationic epoxy may be used as part of the UV top coat. One suitable cationic epoxy has a viscosity range of from about 50 to about 500 cps (Brookfield, RVF4 @ 10 rpm). Other cationic epoxies may have varying viscosity ranges that are also suitable in preferred embodiments. In another embodiment an acrylic resin impregnated paper with an electron beam cured acrylic topcoat is used. In another embodiment, the coated paper comprises a UV cured epoxy coated glassine paper. In one embodiment, a preferred outer shell is coated paper with a thickness ranging from about 0.001 to about 0.003 inches, including about 0.0015, 0.002, 0.0025 inches and ranges encompassing these amounts. Preferred outer shell materials preferably demonstrate one or more of the following characteristics depending on the application: provide a moisture barrier, support for handling, provide a bushing effect for improved accuracy, protect against pressure foot damage related to lose debris and/or a damaged pressure foot, are hard, are minimally abrasive so as not to degrade the drill bit and by extension the hole quality, are substantially flat, are substantially smooth, provide substantially no contamination of other printed circuit manufacturing processes.
In one embodiment, a preferred backup board further comprises a paper layer, also referred to herein as a resistance sheet. As presently contemplated, suitable paper layers include but are not limited to coated or uncoated paper. For example, phenolic paper or coated paper as described herein supra may be used. In one embodiment, paper layers preferably demonstrate one or more of the following characteristics: provide rigidity sufficient to decrease burring without substantially decreasing drill life, are substantially non-contaminating, and are substantially flat.
In one embodiment, a preferred backup board further comprises an adhesive. In one embodiment, adhesive thickness preferably ranges from about 0.0001 inches to about 0.005 inches, but also including about 0.0005, 0.0008, 0.001, and 0.003 inches and ranges encompassing these amounts. In another embodiment, the adhesive is an epoxy. Preferred epoxies are preferably room temperature curable with accelerated cure rate at elevated temperatures (e.g. 15 minute cure time at 200° F.) and/or compatible with post drilling printed circuit processes (e.g. non-contaminating to other printed circuit processes). In certain embodiments, it is desirable to have a shorter cure time as this allows for decreased production time. In other embodiments, if the board is heated it is preferable that the curing temperature of the epoxy does not significantly exceed the melt temperature of the lubricant. In one embodiment, preferred epoxies include, but are not limited to, two-part room temperature cured epoxies, polyimide cured epoxies, two-part Bisphenol A epoxies, and diglycidyl ether of Bisphenol A epoxies. In one embodiment, the epoxy has a resin base and a curing agent wherein the resin base has a viscosity ranging from about 3500 to about 4500 centipoise (Brookfield #4 at 20 rpm, 77° F.) and the curing agent has a viscosity ranging from about 3000 to about 4000 centipoise (Brookfield #4 at 20 rpm, 77° F.). In another preferred embodiment, an epoxy resin is used. Those of skill in the art will understand however that other suitable epoxies and/or adhesives may be used.
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Alternatively, the operator will place the four piece set 110,
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One of skill in the art will understand that in embodiments described herein comprising more than one substantially separate and distinct layer of lubricant, the lubricant may be the same type and/or form or they may differ. Those of skill in the art will also understand that in certain embodiments described herein, the outer shell materials may be the same or they may differ.
One of skill in the art will understand that the non-limiting embodiments depicted in the Figures described above have been exaggerated for ease of understanding. The Figures depict non-limiting embodiments wherein the individual layers have been exaggerated to illustrate each layer. One of skill in the art will understand that the end product will appear to the end user as a single board with distinct layers.
An advantage of preferred backup and entry boards is the flexibility in which the boards are constructed. In preferred embodiments, one of skill in the art can vary one or more of the following items depending on their drilling needs: the outer shell materials, the number of layers of lubricant, the type of lubricant, the form of lubricant, the placement of lubricant, and the choice of core material. In one embodiment, an advantage of preferred backup and entry boards is that the separation of the substantially separate and distinct lubricant layer from the other layers allows for optimization of the lubricant's properties on the drill bit. It is believed that the separation of the lubrication layer allows for an increase in the amount of lubrication provided to the drill by preferred backup and entry boards. Increased lubrication reduces the heat generated by the drill bit which helps reduce damage to the hole wall and increases the life of the drill bit. In embodiments utilizing adhesive, it is believed that the adhesive acts as a barrier layer that helps the lubricant better surround and contact the drill without allowing the drill bit to become clogged by the debris as seen in other lubricated products. This is advantageous in that a reduction in excess debris on the drill bit reduces drill breakage and accuracy reduction due to the excess debris. In embodiments utilizing adhesive, it is believed that the adhesive provides additional stability and rigidity to the board, which helps improve handling and location accuracy.
In the broadest sense, a preferred backup board comprises a core material, one or more lubricant layers, and an outer shell material. In the broadest sense, a preferred entry board comprises one or more lubricants and an outer shell material. In preferred embodiments utilizing two outer shells, the outer shell materials may be the same or they may be different. In other preferred embodiments utilizing more than one layer of lubricant, the lubricants may be the same type and/or form or they may be different. In preferred embodiments, the one or more lubricant layers are preferably substantially separate and distinct layers.
In one embodiment, a preferred backup board comprises an HDF core, a substantially separate and distinct layer of lubricant saturated paper on each side of the core, followed by two outer shells, one on each side of the board. For example, see
In another embodiment, a preferred backup board comprises an HDF core, a substantially separate and distinct layer of extruded lubricant on each side of the core, and two outer shells, one on each side of the board. For example, see
In another embodiment, a preferred backup board comprises an HDF core, a paper layer on each side of the core, a substantially separate and distinct layer of lubricant saturated paper layer on top each paper layer, and two outer shells, one on each side of the board. In another embodiment, a preferred backup board comprises an HDF core, a substantially separate and distinct layer of extruded lubricant on each side of the core, and two outer shells, one on each side of the board. In another embodiment, a preferred backup board comprises an HDF core, a paper layer on each side of the core, a substantially separate and distinct layer of extruded lubricant on top each paper layer, and two outer shells, one on each side of the board. In another embodiment, a preferred backup board comprises an HDF core, a substantially separate and distinct layer of extruded lubricant on one side of the core, and an outer shell on top of the substantially separate and distinct lubricant layer. In another embodiment, a preferred backup board comprises an HDF core, a resistance sheet on one side, a substantially separate and distinct layer of extruded lubricant on top of the resistance sheet, and an outer shell on top of the substantially separate and distinct lubricant layer.
The layers of preferred backup and entry boards may be secured together using one or more of the following: adhesive, tabs, pins, straps, shrink wrap, tape, and other suitable securing devices. In preferred embodiments utilizing an adhesive, preferably the adhesive is a distinct layer. Further, the adhesive may cover the entire layer it is in contact with or only a portion of that layer. In one embodiment, the adhesive is preferably an epoxy. In embodiments utilizing tabs, preferably the tabs are relatively thin (low profile) so as not to raise up the surface of the printed circuit boards stacked on top of the backup board or change the flatness characteristics of the backup.
In some embodiments, all layers will be attached together and utilized as such, see for example
In some embodiments, repeated drilling into the core may cause the substantially separate and distinct lubricant layer to sag through the holes. In preferred embodiments, one or more resistance sheets are provided to support the substantially separate and distinct lubricant layer.
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In one embodiment, an entry board comprises a first outer shell, a substantially separate and distinct lubricant layer (e.g. extruded lubricant layer and/or lubricant saturated paper), and a second outer shell, wherein the layers are in the order recited. For example, see
In another embodiment the entry board preferably comprises a first outer shell material, a substantially separate and distinct lubricant layer (e.g. extruded lubricant, hot melt lubricant, and/or lubricant saturated paper), and a second outer shell wherein the layers are in the order recited and include adhesive between each layer. In another embodiment, the entry board comprises two or more layers of substantially separate and distinct lubricant layers between the two outer shells, wherein adhesive is included between each layer. In certain embodiments wherein more than one substantially separate and distinct lubricant layer is present, the lubricants may be the same type and/or form or they. may differ. In other embodiments, the outer shell materials may be the same or they may differ. For example, one side may have one outer shell of phenolic and the other side an outer shell of aluminum. In another example, one side may have an outer shell of coated or uncoated paper while the other side may have an outer shell of phenolic or aluminum.
In other embodiments the entry board comprises a first outer shell material, a substantially separate and distinct lubricant layer (e.g. extruded lubricant hot melt lubricant, and/or lubricant saturated paper), and a second outer shell material, wherein the three layers are in the order recited and are provided to the drill operator as one bundle without adhesive. In another embodiment, the entry board comprises two or more layers of substantially separate and distinct lubricant layers (e.g. extruded lubricant, hot melt lubricant, or lubricant saturated paper) between the two outer shells. In certain embodiments wherein more than one substantially separate and distinct lubricant layer is present, the lubricants may be the same type and/or they may differ. In other embodiments, the outer shell materials may be the same or they may differ. For example, one side may have one outer shell of phenolic and the other side an outer shell of aluminum.
In other embodiments the entry board comprises a first outer shell material, a substantially separate and distinct lubricant layer (e.g. extruded lubricant hot melt lubricant, and/or lubricant saturated paper), a core, a substantially separate and distinct lubricant layer, and a second outer shell material, wherein the layers are in the order recited and adhesive is used between each layer to secure the layers. In another embodiment, the layers are in the order recited and are provided to the drill operator as one bundle without adhesive.
The various methods and techniques described above provide a number of ways to carry out the invention. Of course, it is to be understood that not necessarily all objectives or advantages described may be achieved in accordance with any particular embodiment described herein.
Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. Similarly, the various features and steps discussed above, as well as other known equivalents for each such feature or step, can be mixed and matched by one of ordinary skill in this art to perform methods in accordance with principles described herein.
Although the invention has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses and obvious modifications and equivalents thereof. Accordingly, the invention is not intended to be limited by the specific disclosures of preferred embodiments herein.
This application claims priority under 35 U.S.C. 119(e) from provisional application Ser. No. 60/496,436 filed Aug. 20, 2003, entitled Apparatus And Method For Use In Printed Circuit Board Drilling Applications, the disclosure of which is incorporated in its entirety herein by reference.
Number | Date | Country | |
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60496436 | Aug 2003 | US |