Abstract:
A photosensitive resin composition and auxiliary plates for drilling are introduced. The auxiliary plates are made by coating the photosensitive resin composition on aluminum foil and photocuring the coated resin to make the resin bonded on the aluminum foil. The resin composition comprises a first polymer formed by the reaction of 1,2,4,5-pyromellitic dianhydride and polyetheramine; and a second polymer formed by the reaction of polyetheramine and vinyl chloride, wherein the second polymer is a photosensitive polymer. The novel resin composition provided by the present invention can be coated on drilling auxiliary plates. When the drilling auxiliary plates coated with the resin composition are used in a drilling process, it can avoid the coated resin being cracked due to the heat caused by friction of high speed drilling, so it can further enhance the stability, accuracy, and precision of drilling.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a resin composition, especially a coating resin composition that is applied to auxiliary plates used in a drilling process. 
       BACKGROUND OF THE INVENTION 
       [0002]    Printed circuit boards (PCBs) provide electronic connection among electronic components and have been developed for about a hundred years. PCBs are made by using insulating plates as substrates, which are cut to a certain size, and having at least one conductive pattern and holes (such as component holes, fastening holes, or metallizing holes) on the substrates to connect electronic components. A common method of manufacturing multilayer PCBs is stacking copper-plated laminates, placing a cover plate on the obtained stack, drilling small holes from the top of the stack, and then connecting holes by electroplating. Therefore, selecting proper materials of cover plates can usually prevent irregular holes, reduce burrs, and improve positioning accuracy. 
         [0003]    Recently, because electronic components have been assembled intensively on PCBs, width of circuit lines and intervals between circuit lines have gradually been smaller. Also, drilling speed of drilling equipment has been increased, drilling process has been shorten, numbers of substrate layers has gradually increased, and it requires the diameters of holes to be smaller than 0.25 mm. Therefore, in the manufacturing process of PCBs, positioning accuracy of drilling has great impact on the processing quality of PCBs. Controlling positioning accuracy of drilling is a key factor in the manufacturing process of PCBs. In order to meet the requirements of reliability, precision, and improvement of drilling quality and drilling positioning accuracy, PCB manufacturers have used cover plates made of aluminum foil coated with lubricating resin on single side or both sides in drilling process. However, due to low melting point, the lubricating resin coated on the covers has problems of flowing over, residue, or even blocking holes. During drilling process, an instantaneous temperature reaches approximately 200° C. due to friction between drill bits and PCBs to be drilled, but the melting point of known lubricating resin is about 60° C. Secondly, because lubricating resin does not adheres well to aluminum foil, resin with high hardiness is often chosen to be the undercoat. This method is complicated, and if the undercoat resin remains in the holes on PCBs, it will cause problems such as broken copper or diffusion of coating during electroplating process. 
         [0004]    Japanese patent publication H04-92488 discloses a drilling method by using polyethylene glycol, wherein polyethylene glycol has 600-9000 of molecular weight. In addition, Japanese patent publication H06-344297 discloses a lubricant sheet for drilling that is formed of a mixture of polyetherester and a water-soluble lubricant, and the lubricant sheet is arranged on one surface or the two surfaces of the laminate. Although the methods mentioned above improved drilling quality, low melting points of the coating resin cause curling problems, which lead to tilting problems of drill bits and decreasing positioning accuracy. 
         [0005]    Taiwanese Patent No. 566064 discloses an entry sheet for drilling for a printed circuit board, which comprises a water-soluble resin and a water-insoluble lubricant as essential components, and a cover board for drilling for a printed circuit board, which comprises the entry sheet, a metal foil having a thickness of 5 to 200 μm, and a thermosetting resin layer having an average thickness of 1 to 10 μm. However, the method mentioned above must have an additional thermosetting resin layer, which increases complexity of the manufacturing process, and the high hardness of the resin may lead to drill bits slipping, which causes shifting of holes, or drill bits breaking. 
         [0006]    Taiwanese patent publication No. 201315311 discloses a drilling backing plate for a printed circuit board (PCB), including a base layer and a lubricating copolymer. The lubricating copolymer is bonded on the base layer and is formed by an ingredient having water-soluble properties and non-water-soluble properties through reaction. The formed drilling backing plate has the functions of lubricating drill bits, cooling, reducing breakage of drill bits, and enhancing drilling accuracy. However, the method mentioned above must have a high temperature baking process to cure the copolymer after the lubricating copolymer is coated. In addition to extending manufacturing time, the baked resin layer may have problems of inconsistent functions and uneven coating thickness due to inconsistent molecular weights of the resin and different evaporation rates of solvent, which may hinder the following drilling application. The concern of inconsistent molecular weights may lead to problems of drill bit getting stuck, degumming of coating layers, and contaminating walls of the drilled holes. 
         [0007]    Therefore, developing coating resin compositions for short manufacturing time, high yields, and high positioning accuracy and applying the compositions to auxiliary plates for drilling PCBs are goals that PCB manufacturers are eager to achieve. 
       SUMMARY OF THE INVENTION 
       [0008]    Given the shortcomings of the prior art mentioned above, the inventors acknowledged that improvements are needed, worked on overcoming the shortcomings with their years of experience, and finally invented a coating resin composition for drilling PCBs. 
         [0009]    To achieve the above object, the present invention provides a resin composition, comprising: a first polymer formed by the reaction of 1,2,4,5-pyromellitic dianhydride and polyetheramine; and a second polymer formed by the reaction of polyetheramine and vinyl chloride, wherein the second polymer is a photosensitive polymer. 
         [0010]    The first polymer of the resin composition mentioned above has a structure of the following formula (I) 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    where n is an integer from 2 to 100, and m is an integer from 1 to 1000. 
         [0011]    The second polymer of the resin composition mentioned above has a structure of the following formula (II) 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein, o is an integer from 2 to 100. 
         [0012]    The resin composition mentioned above further comprises an additive selected from the group consisting of photoinitiator, defoamants, leveling agents, and solvents. 
         [0013]    The resin composition of the composition mentioned above further comprises water-soluble resin. 
         [0014]    The amount of the photoinitiator of the resin composition mentioned above is 1 to 10% by weight of the total resin composition. 
         [0015]    The present invention provides a novel resin composition, which can be coated on a drilling auxiliary plate. When the drilling auxiliary plate of the resin composition is used in the manufacturing process of drilling PCBs, the effects of short production time, high processing yields, and high positioning accuracy can be achieved. When a photoinitiator is added, the problems caused by baking the lubricating coating layer on the auxiliary plate at high temperature in prior art can be solved effectively. 
         [0016]    Accordingly, another purpose of the present invention is to provide a drilling auxiliary plate for printed circuit board, comprising a substrate; and a lubricating resin layer bonded on the substrate, wherein the lubricating resin layer is made by coating the resin composition mentioned above on the substrate and curing the resin composition by illuminating or baking. 
         [0017]    The substrate of the drilling auxiliary plate of the present invention is aluminum foil. The material of the aluminum foil may be pure aluminum, hard aluminum alloys, or semi-hard aluminum alloys, preferably pure aluminum. The thickness of the aluminum foil is 0.03 mm to 0.30 mm, preferably 0.05 mm to 0.20 mm. When the aluminum foil is thinner than the minimum thickness mentioned above, the positioning accuracy of drilling decreases. When the aluminum foil is thicker than the maximum limit mentioned above, drill bits damage badly. 
         [0018]    When the resin composition of the present invention is coated on the substrate, the thickness of the coating layer is 0.01 mm to 0.40 mm, preferably 0.02 mm to 0.25 mm. When the coating layer is thinner than the minimum thickness mentioned above, the dried coating layer cannot lubricate the drill bit. When the coating layer is thicker than the maximum limit, the dried coating layer may twine around the drill bit. 
         [0019]    When the drilling auxiliary plate of the present invention is used, the drilling auxiliary plate is placed on the surface of a printed circuit board, so the metal substrate of the drilling auxiliary plate is in contact with the material of the printed circuit board, and a drill bit starts to drill from the side coated with the coating resin composition. 
         [0020]    When the coating resin composition for PCB drilling of the present invention is the type of a photoreactive functional group with a photoinitiator, ultraviolet (UV) light or electron beam radiation can be used to cure the coating resin composition. UV light is commonly used in which irradiation time is 1 to 600 seconds, and UV wavelength is 250 nm to 450 nm. 
         [0021]    When the coating resin composition of the present invention is added with a photoinitiator, the step of curing resin can be performed at room temperature without a baking process. In addition, no solvent needs to be added in principle, which can further enhance thickness uniformity of the cured resin layer. 
         [0022]    The drilling auxiliary plate of the present invention has the following advantages compared to the prior art. (1) A photoinitiator can be used in the resin composition of the present invention to initiate polymerization without the defect of non-uniform thickness of the dried coating layer caused by the heating process when a thermal initiator is used, and with effective reduction in polymerization time during the manufacturing process. (2) No extra resins, lubricants, or other additives is needed to prepare the resin composition of the present invention, so that the adhesion of the coating layer to the metal substrate is improved, and the complexity of the manufacturing process is reduced. 
         [0023]    To further disclose the present invention so that a person having ordinary skill in the art that the present invention pertains to can practice the invention, the invention is further illustrated by the following examples. However, it should be noted that the following examples are only used to further exemplify the present invention without limiting the scope of the invention. In addition, any modifications and changes obtained by a person having ordinary skill in the art that the present invention pertains to, without departing from the spirit of the present invention, belong to the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is the schematic diagram of the drilling auxiliary plate of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    In order to make the purpose, features, and effects of the invention fully understood, the invention is described in detail by the following embodiments. The description is shown as follows. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Drilling results of drilling auxiliary plates of Examples 1~3 and Comparative examples 1~6. 
               
             
          
           
               
                   
                   
                   
                   
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
               
               
                   
                   
                   
                   
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
               
               
                   
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
               
               
                 Items 
                 ple 1 
                 ple 2 
                 ple 3 
                 ple 1 
                 ple 2 
                 ple 3 
                 ple 4 
                 ple 5 
                 ple 6 
               
               
                   
               
             
          
           
               
                 Proportion 
                 Formula(I) 
                 1 
                 1 
                 2 
                 1 
                 0 
                 — 
                 — 
                 — 
                 — 
               
               
                   
                 Formula (II) 
                 1 
                 2 
                 1 
                 0 
                 1 
                 — 
                 — 
                 — 
                 — 
               
               
                 Test 
                 Cpk 
                 2.84 
                 3.06 
                 2.04 
                 1.07 
                 1.39 
                 — 
                 1.34 
                   
                 1.23 
               
               
                 Results of 
                 Shift 
                 35 
                 26 
                 42 
                 89 
                 62 
                 breaking 
                 68 
                 breaking 
                 82 
               
               
                 Drilling 
                 Avg + 4σ(μm) 
                   
                   
                   
                   
                   
                 drill bits 
                   
                 drill bits 
               
               
                   
                 Roughness of 
                 8 
                 6 
                 7 
                 38 
                 28 
                 breaking 
                 25 
                 breaking 
                 35 
               
               
                   
                 Hole Wall(μm) 
                   
                   
                   
                   
                   
                 drill bits 
                   
                 drill bits 
               
               
                   
                 Rate of breaking 
                 0 
                 0 
                 0 
                 0 
                 0 
                 98.5% 
                 5% 
                 94% 
                 7% 
               
               
                   
                 drill bits(%) 
               
               
                   
                 (Number of 
               
               
                   
                 breaking drill 
               
               
                   
                 bits/Total 
               
               
                   
                 number of 
               
               
                   
                 drill bits) 
               
               
                   
               
             
          
         
       
     
         [0026]    The resin compositions and the drilling auxiliary plates for PCBs of the present invention are described in detail in the following Examples 1˜3. In addition, the effects of the resin compositions and the drilling auxiliary plates of PCBs of the present invention are compared with the effects of the compositions of Comparative Examples 1˜6. 
         [0027]    As shown in  FIG. 1 , the drilling auxiliary plates  1  for PCBs of the present invention comprises: a substrate  10 , and a lubricating resin layer  20  bonded on the substrate, wherein the lubricating resin layer is made by coating the resin compositions of the following Examples 1˜3 on the substrate and curing the resin compositions by illuminating or baking. 
       EXAMPLES 
     Example 1 
       [0028]    One mole of polyether amine (Huntsman JEFFAMINE® D-4000) is mixed with 1 mole of 1,2,4,5-Benzenetetracarboxylic dianhydride, and the mixture reacts at 20° C. for 12 hours to form the first polymer of formula (I), in which the reaction is shown as follows: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0029]    wherein n is an integer from 2 to 100, and m is an integer from 1 to 1000. 
         [0030]    In addition, 1 moles of polyether amine (Huntsman JEFFAMINE® D-4000) and 2 mole of vinyl chloride react at 20° C. for 12 hours to form the second polymer of formula (II), in which the reaction is shown as follows: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0031]    wherein o is an integer from 2 to 100. 
         [0032]    One unit of the first polymer of formula (I) and 1 unit of the second polymer of formula (II) are further mixed well with 3% of photoinitiator (1173) and 1% of photosensitizer (ITX) based on the second polymer to produce the resin composition of the present invention. Fifty micrometers in thickness of the resin composition is directly coated on aluminum foil (material: A1N30) with 100 micrometers in thickness and then irradiated by ultraviolet light (UVA, 365 nm) for 2000˜3000 mj/cm to produce a drilling auxiliary plate. The product is stacked on a copper clad laminate and evaluated by drilling with a 0.1 mm diameter drill bit for 300,000 rpm. The drilling results are shown in Table 1. 
         [0033]    The first polymer and the second polymer comprises groups such as hydroxyl acid group, ether, and amide, and the functional groups allow the resin composition to bind aluminum foil well, so there is less friction during drilling process. The good binding capacity allows the coating resin layer not to fall off easily and not to be sticky when being made a roll, and no undercoat is needed to be coated on the aluminum foil before coating the resin composition. In addition, the first polymer of formula (I) has a benzene ring that has thermal tolerance, and the photopolymerized second polymer of formula (II) enhances degree of crosslinking resulting in improving thermal tolerance, so the coating resin layer has a good heat resistant structure, and when the drilling auxiliary plate of the Example is used in the drilling process, the coating resin layer does not wind around the drill bits, and the debris is not sticky so that it can be removed easily. 
       Example 2 
       [0034]    The first polymer of formula (I) and the second polymer of formula (II) are polymerized by the method of Example 1, and the product is coated and drilled under the same condition as Example 1. The composition comprises polymers of formula (I) and formula (II), wherein the proportion of the polymer of formula (I) and the polymer of formula (II) is 1:2, and the drilling auxiliary plate is made under the same condition of photoreaction as Example 1. The drilling results are shown in Table 1. 
       Example 3 
       [0035]    The polymers of formula (I) and formula (II) are polymerized by the method of Example 1, and the product is coated and drilled under the same condition as Example 1. The composition comprises polymers of formula (I) and formula (II), wherein the proportion of the polymer of formula (I) and the polymer of formula (II) is 2:1, and the drilling auxiliary plate is made under the same condition of photoreaction as Example 1. The drilling results are shown in Table 1. 
       Comparative Example 1 
       [0036]    The first polymer of formula (I) is polymerized by the method of Example 1, and the product is coated and drilled under the same condition as Example 1. The composition comprises only the first polymer of formula (I) without photo-reactivity, so the drilling auxiliary plate is made by heat curing at 160° C. for 30 minutes. The drilling results are shown in Table 1. 
       Comparative Example 2 
       [0037]    The second polymer of formula (II) is polymerized by the method of Example 1, and the product is coated and drilled under the same condition as Example 1. The composition comprises only polymer of formula (II), and the drilling auxiliary plate is made under the same condition of photoreaction as Example 1. The drilling results are shown in Table 1. 
       Comparative Example 3 
       [0038]    Drilling evaluation is performed with a 0.1 mm diameter drill bit for 300,000 rpm by the test method of Example 1. Aluminum foil (material: A1N30) with 100 micrometers in thickness is directly tested for drilling evaluation. The drill bit shifts and breaks easily during the experiment. The results are shown in Table 1. 
       Comparative Example 4 
       [0039]    Drilling evaluation is performed with a 0.1 mm diameter drill bit for 300,000 rpm by the test method of Example 1. Fifty micrometers in thickness of aqueous resin of polyethylene oxide and polyether polyol is coated on aluminum foil (material: A1N30) with 100 micrometers in thickness to produce a drilling auxiliary plate. The drilling auxiliary plate is tested for drilling evaluation. The drill bit shifts and breaks easily during the experiment. The results are shown in Table 1. 
       Comparative Example 5 
       [0040]    Drilling evaluation is performed with a 0.1 mm diameter drill bit for 300,000 rpm by the test method of Example 1. Fifty micrometers in thickness of the mixture of bisphenol A type epoxy resin (supplier: Nan Ya Plastics Corporation, NY454A80) and curing agent is directly coated on aluminum foil (material: A1N30) with 100 micrometers in thickness and then baked at 120° C. for 60 minutes to produce a drilling auxiliary plate. The drilling auxiliary plate is tested for drilling evaluation. The drill bit shifts and breaks easily during the experiment. The results are shown in Table 1. 
       Comparative Example 6 
       [0041]    Drilling evaluation is performed with a 0.1 mm diameter drill bit for 300,000 rpm by the test method of Example 1. Eight micrometers in thickness of the mixture of bisphenol A type epoxy resin (supplier: Nan Ya Plastics Corporation, NY454A80) and curing agent is directly coated on aluminum foil (material: A1N30) with 100 micrometers in thickness and then baked at 120° C. for 60 minutes, and 42 micrometers in thickness of aqueous resin of polyethylene oxide and polyether polyol is coated and then baked at 120° C. for 60 minutes to produce a drilling auxiliary plate. The drilling auxiliary plate is tested for drilling evaluation. The drill bit shifts and breaks easily during the experiment. The results are shown in Table 1. 
         [0042]    The resin composition of the present invention contains a photoreactive functional group, which is the —C═C structure of the polymer of formula (II). The functional group allows the resin composition to form a lubricating resin layer after being cured by Photopolymerization, without a time-consuming baking process, to effectively simplify the manufacturing process of drilling auxiliary plates and shorten production time. 
         [0043]    Furthermore, adding photo-enhancer and photo-stabilizer can improve stability and the photo-curing feature of the lubricating resin layer. Adding defoamants, leveling agents, and solvents allows the coating resin composition to be more easily coated evenly on aluminum foil by a spin coating method. 
         [0044]    It should be understood that the additives used in the Examples is not limited to being used in the coating resin composition of the particular examples. A person having ordinary skill in the art that the invention pertains to can use additives optionally to further improve the features of the coating resin composition of the present invention. 
         [0045]    In the resin composition of the present invention, the first polymer has —COOH functional groups, which can form intermolecular hydrogen bonds with the —NH— functional groups of the second polymer, to form a structure of the following formula (III), wherein the broken lines represent intermolecular hydrogen bonds. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0046]    In addition to the structure of formula (III) above, in the resin composition of the present invention, a single repeating unit of the first polymer can form intermolecular hydrogen bonds with two different second polymers to form the structure of the following formula (IV). 
         [0000]    
       
                 
         
             
             
         
       
     
         [0047]    Moreover, the first polymer has a benzene ring structure, and the resin composition of the present invention is characterized by the structures of intermolecular hydrogen bonds and the benzene ring to make the lubricating resin layer have great crystallinity and lubricating ability. The tests show that there are no cracks produced after curing. In contrast, some of the prior art uses polyethylene glycol (PEG) and/or polyurethane (PU) as the main materials of the coating resin composition, and cracks appear in the lubricating resin layer after curing due to over crystallization and poor thermal tolerance. When a drill bit starts to drill at a crack, the drill bit directly touch aluminum foil, which means the lubricating resin layer loses lubricating function it supposed to have. 
         [0048]    It is generally thought that Shore D hardness of lubricating resin layer of drilling auxiliary plate should be preferably controlled within the range of 20˜40, not more than 40, in order to avoid too much resistance at the beginning of drilling, which can cause increasing rate of breaking drill bits. However, in the drilling process of the drilling auxiliary plate of the Examples, the temperature at the drilling location increases to about 200° C. because of friction of the drill bit, and the lubricating resin layer can be melted into a liquid state, which does not have too much resistance to the drill bit and provides great lubricating ability to improve positioning accuracy of drilling. Furthermore, the feature that the lubricating resin layer of the present invention melts into liquid at about 200° C. allows Shore D hardness of lubricating resin layer to be 40 or even higher without increasing rate of breaking drill bits. The drilling auxiliary plate of the present invention successfully gets rid of the technical preconception about that Shore D hardness of lubricating resin layer cannot exceed 40. 
         [0049]    As mentioned above, the present invention is in full compliance with the patentability requirements: novelty, inventive step, and industrial application. For novelty and inventive step, the present invention provides a novel coating resin composition for being coated on drilling auxiliary plates. When the composition is used in the drilling process of PCBs, it has the effects of shortening production time, increasing yields, and improving positioning accuracy. For industrial application, using the products derived from the invention should fully meet the current needs of the industry. 
         [0050]    The invention has been disclosed in the preferred Examples above. However, those skilled in the art should appreciate that the Examples are used only to illustrate the present invention and should not be construed as limiting the scope of the invention. It should be noted that all the changes and replacement equivalent to the Examples should be included within the scope of the invention. Hence, the scope of the invention shall be defined in the following claims.