Abstract:
At a package for electronic parts forming process, in a package forming method for decreasing stress and stress concentration and obtaining a desired warp and flatness, in particular, according to cutting protruding part process, a package forming method wherein a package for accommodating in recessed part formed one face of a metal plate, forming the recessed part by pressing from the face of the metal plate, and by forming the recessed part protruding part formed bulgingly from one face of the metal plate is cut by cutting tool and a bottom which is rolled up in a cavity shaped and is thinner size than that of the metal plate is formed cavity shaped at the recessed bottom face. Protruding part formed bulgingly in another face of the metal plate is cut by cutting tool dividedly in more than one times and cutting direction is differed in alternately facing direction, stress by cutting is almost cancelled.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a cavity shaped package having a recessed portion for accommodating electronic parts such as an integrated circuit, hybrid circuits and so on, in particular, a method of forming a package for electronic parts which is made from a metal plate.  
           [0003]    2. Description of Related Art  
           [0004]    Through the progress of information devices such as personal computers and so on in recent years, electronic parts such as semiconductor IC circuits or hybrid circuits have been advanced into higher density and higher processing speed, and the information devices using these electronic parts are becoming more precise and more miniaturized. On the other hands, higher density and higher processing speed of these electronic parts increases the amount of heat generated therein. Thus, heat sink means having high efficiency of heat radiation is required. However, the problem is that such miniaturized devices incorporating electronic parts cannot secure enough space for heat sink means that have necessary efficiency of heat radiation due to the miniaturization thereof.  
           [0005]    In order to solve the problem, a cavity type package comprising a metal plate called “stiffener”, which has a window or a recess at the center for accommodating electronic parts, has been occurred. The package allows the amount of heat generated from the electronic parts to be evacuated by the metal plate of the stiffener. Such package has in one body both functions as a heat spreader and as a stiffener for reinforcing the package. The package made from a metal plate will be an alternative to a conventional package, for example, made from ceramics since the former is superior to the latter in the heat sink function,  
           [0006]    [0006]FIGS. 7 and 8 show a package of a semiconductor IC circuit as an example applying abovementioned package. The raw materials of the package  1  is selected from one of metal materials, which has a high thermal conductivity required as a heat spreader and for which plastically deforming processing is applicable, such as cupper alloy stainless steel, aluminum and so on.  
           [0007]    An approximately rectangular recess portion  2  having a bottom portion  1   c  with a predetermined thickness is formed at the center of the surface on one side  1   a  of the package  1 . That is, this package  1  is formed in a cavity shape as a whole. A wiring board  4 , which is a TAB or flexible printed board, a usual pointed board, etc., is stuck and secured to the one side  1   a  of the package  1  by means of an adhesive. The wiring board  4  may be a layer on which a wiring circuit is formed and by which the wiring circuit is insulated from the package  1 . An opening  4   a  having an approximately same size as the recess portion  2  is formed in this wiring board  4 . A terminal portion  4   t  having a number of terminals is formed by printed wiring on the periphery of this opening  4   a  with a wire width and a pitch of about 37 nm. The terminals of the terminal portion  4   t  are electrically connected by printed wiring to externally connecting terminals (not indicated in the figures), which are formed on an outer periphery of the wiring board  4 .  
           [0008]    Further a chip  5  of electronic parts such as a semiconductor integrated circuit is accommodated in the recess portion  2  formed on the one side  1   a  of the package  1 . The chip  5  is stuck to the bottom portion  1   c  of the recess portion  2  by means of an adhesive in a state where a surface of the chip  5  and that of the bottom portion  1   c  are tightly fitted. What is important in this sticking using an adhesive is that no bubbles should be produced between the chip  5  and the bottom portion  1   c  of the recess portion  2 . This is because the bubbles are expanded and the chip  5  may be thereby peeled off in case where heat is produced during working of the electronic parts in the chip  5  and in case where heat is subjected to the package  1  during its assembling to an apparatus. Thus, the bottom portion  1   c  of the recess portion  2  should be formed in such an evenness that warp is smaller than 30 nm.  
           [0009]    On the upper surface of the chip  5  there are disposed a number of terminals  5   t  with a same wire width and a same pitch as those in the terminal portion  4   t  formed on the wiring board  4 . Each of the terminals  5   t  of the chip  5  and each terminal of the terminal portion  4   t  of the wiring board  4  are electrically connected by bonding wires  7 , as indicated in FIG. 7. Further sealing agent  8  is injected into the recess portion  2  of the package  1  to seal the chip  5  and the bonding wires  7 .  
           [0010]    When the electronic parts such as an integrated circuit packed in the package  1  as described above is mounted onto a circuit board of an electronic apparatus not indicated in the figure, solder balls  9  are placed on the externally connecting terminals formed on an outer periphery of the wiring board  4  and they are melted by heating in a state where the package  1  is provisionary fixed at predetermined position on the circuit board of the electronic apparatus. In this way the electronic parts packed in the package  1  and the circuit board of the electronic apparatus are connected electrically via the wiring board  4  without any damages to the package  1  and its electronic parts due to expanding the bubbles between the chip  5  and the bottom portion  1   c.    
           [0011]    On the other hand, when a semiconductor IC circuit is exothermic in operating, the package  1  itself has a function of heat spreader, thereby, heat is conducted the package  1  and is released.  
           [0012]    In a forming method of above constituted cavity type package, for example, there is a method that a concave part is pressing processed using a pressing punch by press machine or by chemically etching process, a concave part is formed in a metal plate so that keep a bottom of a thin plate.  
           [0013]    However, in a pressing process by press machine metal part of volume of the recess part is pushed into a bottom part and periphery. The periphery metal part is curled, then the flatness of the part is not able to correct state. Thereby, a package acquired necessity flatness has a fatal problem. The chemically etching process takes long time, so there are troublesome that the method is not suited in mass production and takes more cost in necessity. Moreover, precision by limiting to control etching process is worth, there is troublesome that practical use has a limit.  
           [0014]    Inventors have proposed in U.S. Pat. No. 6,145,365 a preferred method for forming above mentioned type package made from a metal plate. FIG. 9(A) to  9 (D) shows the proposed method in summary. The method will be described herein below.  
           [0015]    [0015]FIG. 9(A) shows a metal plate  100  that is positioned with respect to a die  104  of a press machine. FIG. 9(B) shows a pressing process, where the metal plate  100  is pressed recessed by a punch  105  of the press machine onto one side surface  100   a  so that the recessed part  102  is formed. At the same time, a protruding part  103  is formed in ledge shape on another side surface  100   b  of the metal plate  100 .  
           [0016]    FIGS.  9 (C) and  9 (D) show cutting process, wherein a cutter  106  shaves off the protruding part  103  formed on the surface  100   b  so as to form a thin bottom  100   c  and to make the surface  100   b  flat. In this cutting process, to avoid displacement of the bottom plate  100   c  in the direction to the recessed part  102 , the bottom plate  100   c  is pressivelly supported by a supporting tool  107 . According to the abovementioned processes, the recessed part  102  for accommodating a chip of electronic parts is formed in the metal plate  100 , which has a bottom plate  100   c  having a predetermined comparatively thin thickness as the bottom of the recessed part  102 . Thereby, the recessed part  102  of predetermined depth is formed by pressing and cutting without any damages to the bottom plate  100   c.    
           [0017]    In the above methods, it is possible to form the recessed part  102  having a predetermined shape only on one side of the metal plate without giving the metal plate any remarkable stress or changing the composition of the metal plate because metal corresponding to the recessed part  102  is displaced to the protruding part  103  on the other side of the metal plate by plastically deforming processing by means of the press. However, in the cutting process, it is inevitable that the cutter  106  pulls the metal of the protruding part  103  around the cutting line by its movement. Therefore, the metal plate suffers a stress, especially at and around the bottom part  100   c.    
           [0018]    Further, into the portion where the cutting by the cutter  106  ends, shown in left side on FIG. 9(D), a stress of pressure by the movement of the cutter  106  is concentrated. Such stresses provided by cutting process of the protruding part  103  lead to the problems that the dimensions of the package may change over time and that a time-varying warp may occur. Thereby, as mentioned above, in a package of electronic parts that requires such evenness that warp within 30 nm, the time-varying changes of dimensions and evenness become a fatal defect.  
         SUMMARY OF THE INVENTION  
         [0019]    In order to solve such problems, the present invention, a package for accommodating in a recessed part formed one face of a metal plate, in package forming method for electronic parts formed cavity shaped which has thinner bottom part than the metal plate characterized in that, the package is formed the recessed part by pressing press machine or the like from one face of the metal plate and protruding part formed bulgingly in another face of the metal plate, by forming of the recessed part is cut by cutting tool dividedly in more than one and a cutting direction is differed in alternately facing to each other, so stress by cutting is almost cancelled.  
           [0020]    Moreover, in the present invention, pressing process for pressing recessed part from one face of the metal plate and cutting process for cutting protruding part of another face of the metal plate are performed repeatedly more than one, and forming in stepwise desired depth of recessed and protruding parts in every forming frequencies a cutting direction may be differed in alternately facing to each other.  
           [0021]    Moreover, in the present invention, pressing recessed part of predetermined depth in a face of the metal plate, protruding part of another face (opposite site face) of the metal plate is formed, in every cutting the protruding part dividedly in stepwise, a cutting direction may be differed in alternately facing to each other.  
           [0022]    Moreover, in the present invention, when protruding part of another face of the metal plate is formed in every cutting the protruding part dividedly in stepwise, number of times of a cutting direction in alternately facing to each other may be the same.  
           [0023]    Furthermore, in the present invention, predetermined recessed part which is shallower than thickness size of the metal plate from a face of the metal plate and the protruding part which is a little small than the recessed part in another face of the metal plate may be formed in every cutting the protruding part dividedly in stepwise, a cutting direction may be differed in alternately facing to each other. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    FIGS.  1 (A) to  1 (G) are diagrams for explaining a processing procedure of an embodiment of the package forming method according to the present invention;  
         [0025]    [0025]FIG. 2(A) and  2 (B) are plan views showing examples of the cutters and the cutting processing by them according to the present invention;  
         [0026]    FIGS.  3 (A) and  3 (B) are diagrams for explaining a processing procedure of another example of cutting the protruding portion in the steps for forming the package according to the present invention;  
         [0027]    FIGS.  4 (A) and  4 (B) are diagrams for explaining a processing procedure of another example of cutting the protruding portion by a rotating cutter in the steps for forming the package according to the present invention;  
         [0028]    FIGS.  5 (A) and  5 (B) are diagrams for explaining a processing procedure of another example of cutting the protruding portion by a grinder in the steps for forming the package according to the present invention;  
         [0029]    [0029]FIG. 6 is a drawing showing a processing procedure of the method for forming the package by means of a transfer-processing machine according to the present invention;  
         [0030]    [0030]FIG. 7 is an exploded perspective view of a package for electronic parts according to the present invention;  
         [0031]    [0031]FIG. 8 is a cross-sectional view of the package indicated in FIG. 7; and  
         [0032]    [0032]FIG. 9(A) to  9 (D) are diagrams for explaining a processing procedure of the former method for forming a package proposed by the inventor. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    Hereinafter the method for forming a package for electronic parts made of a metal plate according to the present invention will be explained in detail, based on a mode of realization indicated in drawings.  
         [0034]    FIGS.  1 (A) to  1 (G) shows the first embodiment. FIG. 1(A) shows metal plate  10  that forms the package  1  shown in FIG. 7. The metal plate  10  is positioned with respect to a die  11  of a press that has a recess  11   a  at a predetermined portion. The raw material for the metal plate  10  is selected from one of cupper alloy, stainless steel and aluminum or the like. As the metal plate  10 , both a sheet cut into a predetermined size and a rolled band like material can be used.  
         [0035]    [0035]FIG. 1(B) shows a step of the first pressing processing. After the metal plate  10  is positioned on die  11 , a preliminary recess portion  2   a  that is shallower than the recess portion  2  is formed on one side  10   a  of the metal plate  10  by means of a punch  12  of the press. An edge of the punch  12  is formed nearly square form in a predetermined size.  
         [0036]    At the time of forming the preliminary recess portion  2   a , an amount of metal corresponding to the preliminary recess portion  2   a  is displaced to the other side  10   b  by the pressure added by the punch  12 . As the result, a protruding portion  3   a  protruding from the surface on the other side  10   b  of the metal plate  10  is formed so as to have a height h approximately equal to the depth of the preliminary recess portion  2   a . The outer perimeter W 1  of the protruding portion  3   a  is slightly smaller in size than the outer perimeter W 2  of the preliminary recess portion  2   a . Also the protruding portion  3   a  is analogous in shape to and centered under the preliminary recess portion  2   a . Since such a relation in size is set, the protruding portion  3   a  is not cut-off from the metal plate  10  at its edge portion so that it can be always kept joined thereto and that a stress at the cutting processing described later can be minimized. Further, it is desirable to set the height h of the protruding portion  3   a  at such a value that it can be shaved off with the minimum stress at the cutting processing. FIGS.  1 (C) and  2 (D) show a first cutting processing, in which the protruding portion  3   a  formed on the other side  10   b  of the metal plate  10  by the first pressing process is shaved off at its root by means of a cutter  13  so that the cut surface newly obtained by the shaving is coplanar with the other part of the surface of the other side  10   b . The cutter  13  used for the cutting processing has a blade  13   a . As the shape of the blade  13   a , both a straight lined blade whose extremity is straight line as indicated in FIG. 2(A) and an arrow-shaped blade whose extremity is pointed at the center as indicated in FIG. 2(B) are acceptable. But the arrow-shaped blade is more preferable than the straight lined blade in order to minimize the stress during the cutting processing. Moreover, the blade  13   a  of the cutter  13  is desirable to have a gradient type extremity that is sharp-pointed into the direction of its movement.  
         [0037]    The cutter  13  is advanced in the direction indicated by an arrow in FIG. 1(C), that is to say, form the front end to the rear end. As indicated in FIG. 1(D), the first cutting processing terminates when the extremity of the blade  13   a  has reached to the rear end of the protruding portion  3   a . In this cutting processing it is desirable that a supporting tool  14  which support the bottom of the preliminary recess portion  2   a  under pressure is inserted therein in order to prevent the bottom from being displaced inwardly by the cutter  13 . When the cutter  13  cuts the protruding part  3 , the portion of the metal plate  10  where the cutting is executed suffers stress due to concentration of pressure by advancing movement of the cuter  13  toward the rear end and due to tensions pulled by the cutter  13  in the cut surface. Though these kinds of the stresses vary by difference among tenacity of the metal materials, these stresses are dissolved in the second cutting processing described later.  
         [0038]    Next FIG. 1(E) shows a step of the second pressing processing. The second pressing processing is executed by means of the punch  12  and the die  11  of the press so as to make the preliminary recess portion  2   a  formed by the first pressing processing deeper, and to form the recess portion  2  having the final depth and shape required as the package  1 . At the same time, a protruding portion  3  whose height is approximately equal to the increased depth of the recess portion, is formed on the other side  10   b  of the metal plate  10 , similarly to the first pressing processing. The outer size of this protruding portion  3  is slightly smaller than the inner size of the recess portion  2  and the protruding portion  3  is analogous to the recess portion  2 .  
         [0039]    Then a second cutting processing indicated in FIGS.  1 (F) and  1 (G) are executed. The protruding portion  3  formed on the other side  10   b  of the metal plate  10  by the second pressing processing is shaved off at its root by means of the cutter  15  so that the cut surface newly obtained by the shaving is coplanar with the remaining part of the surface of the other side  10   b . As indicated by an arrow in FIGS.  1 (F) and  1 (G), the direction that the cutter  15  advances is reversed to that the cutter  13  has advanced though the second cutting processing is similar to the first cutting processing and the cutter  13  used at this second processing is the same as that has used in the first cutting processing. When the cutter  15  has advanced in the inverse direction with respect to that of the cutter  13 , and has reached at the position indicated in FIG. 1(G), the surface of the other side  10   b  of the metal plate  10  is formed flat and a thin bottom plate  10   c  is formed in the bottom of the recess portion  2 .  
         [0040]    As a result of the second cutting processing, the concentration of stress and stress itself generated in the metal plate  10  at the first cutting processing are almost cancelled or reduced sharply because of the inverse advancing of the cutter  15  with respect to the direction that the cutter  13  has advanced. Also, in the second cutting process, it is desirable that a supporting tool  14  is inserted into the recess portion  3  in order to support the thin bottom plate  10   c  under pressure and to prevent the bottom plate  10   c  from being displaced inwardly by the cutter  15 .  
         [0041]    The cutter  15  used in the second cutting processing is formed as same as the cutter  13  used in the first cutting processing so as to achieve the first and second cutting processing under the same cutting conditions. The cutting condition is so set that the concentration of stress and stress itself may be cancelled. It is another example to accomplish the same cutting condition between the first and second cutting processing that the metal plate  10  is turned horizontally in an inverse direction at each of the first and second cutting processing in order to cut the protruding portions alternately into a regular direction and a counter direction while using one of the cutter  13  and  15 , which moves in one way.  
         [0042]    In general, the required flatness for the bottom plate  10   c  of the package  1  is warp within 30 nm or less and the required flatness for the package  1  as a whole is warp within 70 nm or less. According to the steps described above, the required flatness of the package  1  can be obtained by canceling the concentration of stress and irregular deformation of the bottom plate  10   c . Moreover the package  1  can be prevented from changes with the passage of time due to small range of the concentration of stress and irregular deformation.  
         [0043]    Another Embodiment  
         [0044]    [0044]FIG. 3(A) and (B) show another embodiment of the method for forming a package  1 , in which both the recess portion  2  having a predetermined depth as the package  1  in one side surface  10   a  and the protruding portion  3   b  protruding onto the other side surface  10   b  are formed by one pressing processing. Thereafter the protruding portion  3   b  is cut bit by bit repeatedly in a plurality of times. That is as shown in FIG. 3(A), a first cutting processing is executed in such a way that a part of the thickness of the protruding portion  3   b  along a slice line is shaved off by the cutter  13  advancing from right to left in regular direction. Next, a second cutting processing is executed in such a way that the next part of the thickness of the protruding portion  3   b  along the next slice line is shaved off by the cutter  15  advancing form left to right in the counter direction. Then, the cutter  13  executes a third cutting processing in the same way as the first cutting processing and the cutter  15  executes a forth cutting processing in the same way as the second cutting processing.  
         [0045]    The cutting processing by the cutter  13  and  15  is executed alternately until the remaining part of the protruding portion  3   b  is shaved off at its root and the cut surface newly obtained by the cutting becomes coplanar with remaining part of the surface of the other side  10   b . In this way, since the cutting processing is repeated in a plurality of times changing the advancing directions of the cutters alternately in regular direction and in counter direction, the concentration of stress and irregular deformation of the bottom plate  10   c  caused by the cutter  13  can be canceled or reduced significantly by the movement of the cutter, and vice versa. Further, since the thickness of the protruding portion  3   b  shaved off by one cutting processing sets so small that the infliction of remaining stress and direct stress on the metal plate  10  is prevented and it remains as is, similarly to the example described referring to FIGS.  1 (A) to  1 (G).  
         [0046]    As described above, it is preferable that the each number of times of cutting in regular direction and in counter direction finally becomes same when protruding  3   b  formed on the surface of the other side  10   b  is cut bit by bit in several times. In the example shown in FIG. 3, each number of times in regular direction and in counter direction is two times each but it can be set selectively as desired according to the thickness of a part of the protruding portion  3   b  cut in one time. As so set, the concentration of stress and irregular deformation of the package  1  caused by each cutting processing can be canceled by each next cutting processing in the reverse direction.  
         [0047]    [0047]FIG. 4(A) and  4 (B) show another example of the method in which rotating blades  30  of a milling machine is used as cutting tool instead of the cutter used in the first and second cutting processing shown in aforesaid FIGS.  1 (C) and  1 (F). That is, as shown in FIG. 4(A), after the first pressing processing, the first cutting processing is executed in such way that that the rotating blades  30  cut the protruding part  3   a  advancing from right to left in regular direction so that the cut surface newly obtained by the cutting is coplanar with the remaining part of the surface of the other side  10   b . Then, as shown in FIG. 4(B), in the second cutting processing after the second pressing processing the rotating blades  30  cut the protruding part  3  moving right to left in the counter direction so that the cut surface newly obtained by the cutting becomes coplanar with the remaining part of the surface of the other side  10   b.    
         [0048]    Though the method by the rotating blades of a milling machine affects less stress than that by aforementioned cutter  13  or  15 , there causes and remains still some concentration of the stress. But, since the cutting processing is executed in such a way that the rotating blades of a milling machine moves in a plurality of times alternately in regular direction and in counter direction, the concentration of stress and irregular deformation of the bottom plate  10   c  caused by the rotating blades can be canceled or reduced significantly.  
         [0049]    FIGS.  5 (A) and  5 (B) show modified example of the method shown in FIG. 4(A) and  4 (B) in which a grinder is used as cutting tool instead of the cutters or the rotating blades. That is, as shown in FIG. 5(A), after the first pressing processing, the first cutting processing is executed in such way that that the grinder  31  cut the protruding part  3   a  advancing from right to left in regular direction so that the cut surface newly obtained by the cutting is coplanar with the remaining part of the surface of the other side  10   b . Then, as shown in FIG. 5(B), in the second cutting processing, after the second pressing processing the grinder  31  cut the protruding part  3  moving right to left in the counter direction so that the cut surface newly obtained by the cutting becomes coplanar with the remaining part of the surface of the other side  10   b.    
         [0050]    [0050]FIG. 6 shows a forming method of a package of electronic parts by means of a transfer-processing machine not shown in the drawing. In this embodiment, a rolled metal band  20  is used as the metal plate, which is, for example, made of cupper alloy, stainless steel and aluminum. First, groove holes  24  defining the outline of the package  1  and pilot holes  26  guiding transfer of the metal band  20  are formed in the metal band. Then, the package  1  and intermediate packages  21  to  23  are formed in such a way that they are connected to each other via connecting portions  25 .  
         [0051]    After the processing to form the groove holes  24  and pilot holes  26 , the first press processing is executed so as to form the intermediate package  21  which has a shallow recess portion  2   a  in one side surface  20   a  of the metal band  20  by applying the first pressing processing as shown in FIG. 1(B). Then the intermediate package  21  is transferred for the first cutting processing shown in FIG. 1(C) and  1 (D), where a cutter  13  shaves off the protruding part (not shown in the drawing) formed on the other side surface of the metal band  20  so forming the intermediate package  22 . Next, the intermediate package  22  is transferred for the second pressing processing shown by FIG. 1(E) so as to form recess portion  2  having final depth in one side surface  20   a  of the metal band  20 , wherein the intermediate package  23  having a protruding portion on the other side surface of the metal band  20  is formed. After the intermediate package  23  is transferred for a final processing, that is to say the second cutting processing as shown in FIG. 1(F) and  1 (G), the protruding portion (not shown in the drawing) is shaved off by a cutter  15  so that the final shape of the package  1  is formed. Then, before the package  1  is separated from the metal melt  20 , semiconductor circuit and wiring board are mounted on the package  1 . Finally the package  1  as final product is separated from its intermediates of the metal band by the connecting portions  25 .  
         [0052]    In the abovementioned method of forming a package of electronic parts by means of a transfer-processing machine each of the steps of first and second pressing processes and cutting processes is executed to only one of the package  1  and its intermediates  21  to  23  in one time. It is applicable that the each of the steps is executed to the plurality of intermediates grouped as one unit for same processing. In this case, the each step of first and second pressing processes and cutting processes is applied to each of the units.  
         [0053]    In before mentioned description of embodiments, a semiconductor IC circuit is an example of electronic parts accommodated in the recess portion of the package but another electronic parts for example hybrid circuit, inductor chip or resistor array may adapt as electronic parts. The present invention is not restricted in these embodiments, which may change in an extent without departing from the scope of the invention.  
         [0054]    As described above, in package forming method according to the present invention, the protruding portion, which is formed in ledge shape on one surface of the metal plate opposite to the other surface where the recess portion is formed at the same time, is cut bit by bit repeatedly in a plurality of times changing the advancing directions of the cutting means alternately in regular direction and in counter direction. Thus, the stress and its concentration produced by the cutting in regular direction is cancelled or reduced significantly by the cutting in counter direction, and vice versa. As the result, the package of the electronic parts acquires the required evenness and flatness with little warp. Moreover, reduction of the stress and its concentration on the package prevents the time-varying changes of dimensions and evenness of the package. Accordingly, a high accuracy package for electronic parts can be obtained.