ASSEMBLY APPARATUS

Abstract: A method and apparatus is disclosed for attaching preform to a metallic workpierce, particularly anepoxy preform for use in electronic packages. It hs been known to preform the epoxy sealant and thenposition it onto the metallic base member by hand,leading to slow assembly techniques and inaccurateplacement of the preform onto the base member. Theabove problems are solved by providing an apparatu and a method in which an epoxy preform is stampedfrom a strip (50) and maintained in an upper die asembly (42). The metallic workpiece (48) is indexe underneath the upper die assembly (42) whereupon he epoxy preform is deposited onto the metallic wokpiece (48) and the metallic workpiece is then remved from underneath the upper die assembly.

Description: ASSEMBLY APPARATUS This invention relates generally to the formation of a preform and the attachment thereof to a metal workpiece; and, more particularly, this invention relates to the formation and attachment of an adhesive preform to a metal workpiece. The present invention has particular utility in attaching an adhesive layer to a metal workpiece which may used as a component for metal electronic packages. Such packages are shown and disclosed in U.S. Patent No. 4,897,508. In one form of a metal electronic package such as disclosed in the above-mentioned patent, the package comprises two parts, a base component and a cover or lid component. The base component is generally flat, without sidewalls, and a leadframe is spaced from the base component by a sealant such as an epoxy so it is in a plane which is in alignment with the upper surface or bonding face of the electronic device which is attached to the base member. The wire bonds connecting the bonding face of the metal package and the leadframe may flex upwardly so the upper component or lid of the package includes a cavity in its interior surface to provide the space for the flexing while minimizing overall thickness of the package. A sealant, such as an epoxy, is positioned between the upper surface of the leadframe and the cover or lid component. In practice, it has been common for the epoxy sealant to be preformed and then positioned onto the cover or base member by hand. However, not only is a hand assembly slow, but also proper placement on the cover or lid is important so that excess adhesive is not squeezed out from the edges of the package or into the internal cavity of the package. In accordance with the present invention, it is an object to provide an improved process and apparatus for forming a preform and attaching it to a component of a metal workpiece. A more specific object of the present invention is the provision of an improved process and apparatus for forming an epoxy preform in the proper shape and attaching it to a metal workpiece in the proper location. These and other objects and advantages of the present invention may be achieved through a process and apparatus which includes feeding a strip into a punch and die mechanism, cutting the desired shape from the strip to form a preform and holding it in an upper member and bringing the workpiece into a position below the preform and ejecting the preform from the upper member onto the workpiece. This invention may be better understood by reference to the following description and the accompanying drawings in which: Figure 1 is a cross-sectional view of an electronic package of the type which may utilize a metal workpiece having a epoxy sealant attached thereto in accordance with the present invention; Figure 2 is an isometric view of a first embodiment of the present invention; Figure 3 is a sectional view of an embodiment shown in Figure 2 taken along the lines 3-3 of Figure 2; and Figure 4 is a schematic plan view of a second embodiment of the present invention. Referring to the drawings and in particular Figure 1, an electronic package 10 is shown which includes components that may be made utilizing the process and apparatus of the present invention. The package 10 is comprised of a base component 12 and a cover or lid component 14. The base and cover components are formed from a ductile material such as a metal or metal alloy. Materials which may be used for these components include low coefficient of thermal expansion materials such as KOVAR and Alloy 42. Materials with higher coefficients of thermal expansion and high thermal conductivity to dissipate heat away from the electronic device such as copper, aluminum, and nickel near alloys are also preferred. One particularly preferred material is aluminum or aluminum alloy as described in U.S. Patent No. 4,939,316. As mentioned in that patent, preferred aluminum alloys include those designated by the ASM (American Society for Metals) as 3xxx series. These alloys contain up to about 1.5% by weight manganese, along with other alloying ingredients. One especially preferred aluminum alloy is aluminum alloy 3003 having a nominal composition of about 0.12% by weight copper, about 1.5% by weight manganese and the balance aluminum. A leadframe 16 is disposed between the base component 12 and cover component 14 and extends from the interior of the package to the outside thereof. The leadframe 16 is made from a conductive material having good tensile strength and typically is comprised of copper, iron or their alloys. A sealant 18 bonds the leadframe 16 to the base component 12 and the cover component 14 and also bonds the base component 12 and cover component 14 together. The sealant 18 may be or a suitable polymer adhesive as is well known in the art. A resin adhesive such as an epoxy, for example ABLETRIK 550K manufactured by Abletrik Laboratories of Gardena, California, is one example. The base component 12 may be generally flat and includes a planar internal surface 20. An electronic device 22, for example a semiconductor device, is bonded to the flat internal surface 20 of the base component 12 by a suitable die-attach means. Wire bonds 24 electrically connect the electronic device 22 to the inner portion of the leadframes 16. The wire bonds 24 which electrically connect the leadframes 16 to the bonding sites on the surface of electronic device 22 may be formed from thin strips of copper foil by the process known as tape-automated bonding (TAB) . These wire bonds 24 flex upwardly as shown in Figure 1 and accordingly the upper cover or lid component 14 contains a cavity 26 having a bottom surface 28 parallel to the outside surface 29 and perpendicular sidewalls 30. In some embodiments of metallic packages a vent hole 32 may be provided in the cover component 14 as described more fully in U.S. Patent No. 4,897,508. The vent hole 32 is a vent for reaction by-products created during the cure cycle of the sealant. After the cure cycle is completed, an inert thermally conductive gas such as helium or thermally conductive, electronically non-conductive liquid may optionally be ejected into the package cavity 34 to provide additional thermal dissipation means for the electronic device 22. The vent hole may be in the form of a through bore 36 having a counterbore 38 extending inwardly from the outside surface of the cover as shown in Figure 1. After the packaging is completed, the vent hole may be sealed by applying a suitable patch as, for example, a drop of solder into the counterbore 38 of vent hole. The process and apparatus of the present invention may be used for attaching the sealant 18 to the base component 12 and the cover component 14 prior to the assembly thereof with the leadframe and electronic device. In the embodiment shown in Figure 2, an apparatus 40 for forming the sealant preform shape and attaching it to either the base or cover component of the metal package is shown. Generally, the apparatus 40 comprises a punch and die assembly 41 including an upper die housing 42 and a lower die housing 44, and a transport mechanism 46 for moving a metal workpiece 48 such as the base 12 or cover 14 component of the metallic package of Figure 1 to a position underneath the upper die housing 46. The sealant is fed into the apparatus in the form of an epoxy strip or tape 50. More specifically, the apparatus 40 includes a base 52 upon which the lower die housing 44 is mounted. The lower die housing 44 includes a base block 54 attached to the base 52 by bolts 55 and having a hollow punch 56 extending upwardly therefrom which has a cross-sectional configuration corresponding to that of the epoxy preform 58 to be formed. A stripper plate 60 surrounds the outer periphery of the hollow punch 56 and is mounted for movement relative to the base block 54 and punch 56 by means of headed bolts 62 each having its head 64 mounted in a counterbore 66 in the base plate 54 and its opposite end 68 threadably attached to the stripper plate 60. A spring member 70 surrounds each of the bolts 62 to bias the stripper plate 60 upwardly to a position at which its top surface 72 is flush with the top surface 74 of the punch 56. Two guideposts 76 are mounted in the base 52 and extend upwardly through ears 78 in the base block 54 of the lower die housing 44. The upper die housing 42 is mounted for movement toward and away from the lower die housing 44 on the guideposts 76 and is biased into its raised portion by springs 77 surrounding each of the guideposts 76 and extending between the upper and lower die housings 42 and 44 as shown. The upper die housing 44 includes an upper base plate 80 having ears 82 with openings 84 through which the guideposts 76 extend whereby the upper die housing 42 is guided for vertical movement. A backing plate 86 is positioned flush against the bottom surface 88 of the upper base plate 80. A die member 90 has its upper surface positioned against the backing plate 86. The backing plate 86 and die member 90 are securely attached to the upper base plate 80 by means of alignment pins 92 and threaded bolts 94 as shown. An ejector piston 96 is mounted in an opening 98 extending through the upper base plate 80 and includes a body portion 100 guided for movement within the opening 98 and a post 102 extending upwardly from the body portion 100 above the top surface 104 of the upper base plate 80. Ejector pins 106 are slidably mounted for axial movement in the backing plate 86 and extend upwardly through the backing plate 86 into the opening 98 beneath the ejector piston 96. A center post 108, having a cross-section corresponding to the cross-section of the hollow opening in the punch 56 of the lower die housing 44, and thus, also corresponding to the internal opening in the epoxy preform 58, extends downwardly from the backing plate 86 through an opening 110 in the die member 90. The opening 110 is defined by a surface having a shape conforming to the outer periphery of the epoxy preform. An ejector member 112 having a bottom portion 114 conforming to the shape of the epoxy preform and an upper outwardly extending flange portion 116 is mounted in the die member 90. The bottom portion is positioned between the opening 110 and post 108. The flange portion 116 of the ejector member 112 is positioned within a counterbore 118 in the upper surface of the die member 90 with the bottom portion 114 extending into the opening 110 in the die member 90. The depth of the counterbore 118 is greater than the thickness of the flange portion 116 of the ejector member 112 such that there is a space provided between the flange 116 and the bottom of counterbore 118 when the ejector member 112 is in its upper position whereby the ejector member 112 has limited axial movement in a vertical direction with respect to the die member 90. When the ejector member 112 is in the upper position, the bottom surface 120 of the ejector member 112 is recessed within the die member 90 forming a cavity 122 therein having the shape of the epoxy preform to be stamped out of the strip 50. The transport mechanism 46 is mounted on the base 52 and includes an elongated rectangular transport member 130 adapted to be reciprocated into and out from underneath the upper die housing 42. The transport member 130 has its outer end portion 132 guided by spaced inverted L-shaped brackets 134 mounted on spaced support block 136 as shown. The inner end 138 of the transport member 130 rests on blocks 140 and 142 mounted on the base block 54. When the transport member 130 is in its inner position underneath the upper die housing 42, the inner end 138 rests on both of the spaced blocks 140 and 142. When it is in the withdrawn position, the inner end 138 rests solely on the outer block 140. A metal workpiece receiving cavity 150 is provided in the inner end 138 of the transport member 130 and opens to the upper side thereof. The metal workpiece 48 to which the epoxy preform is to be attached is contained within the cavity 150 for movement with the transport member 130. The transport member 130 is provided with a series of alignment holes 152 outwardly of metal workpiece receiving cavity 150 through which alignment pins 154 which extend downwardly from the upper die assembly 42 are adapted to extend when the transport member 130 is in its inward position and when the upper die assembly 42 is moved into its lower position. The upper die assembly 42 may be raised and lowered by means of a suitable air cylinder 156. Similarly, an air cylinder 158 may be attached to the ejection ram for actuation thereof. The slide assembly may also be reciprocated between its inner and outer positions by means of the air cylinder 160. The air cylinders 136, 138 and 140 may all connect to suitable timing valves (not shown) to activate the mechanisms in the proper sequence to be described below. Other suitable moving members such as air motors, electric motors or the like may be used. Alternatively, handles may be provided for the manual operation of the device. In operation, with the transport member 130 withdrawn, the strip 50 of epoxy sealant is indexed onto the lower die housing 44 beneath the upper die housing 42 by hand or by suitable indexing mechanism. The air cylinder 156 lowers the upper die housing 42 so that the bottom surface of the die member and post 108 in the upper die housing 42 engage and force the strip 50 against the stripper plate 60 and punch 56 in the lower die housing 44. Continual downward movement of the upper die housing 42 causes the stripper plate 60 and epoxy strip 50 to move downwardly relative to the punch 56 thereby cutting out the preform from the strip. The cut preform is forced into the cavity 122 in the bottom surface of the upper die housing 42 so that the preform is retained within the cavity 122 as the upper die housing 42 is moved upwardly. The stripper plate 60 strips the epoxy strip 50 from the punch 56 as the upper die housing 42 is raised. When the upper die housing 42 is raised, the transport member 130 with a suitable metal workpiece positioned within the receiving cavity 150 is indexed beneath the upper die housing 42 and over the lower die housing 44 and epoxy strip 50, and the upper die housing 42 is again lowered. When the upper die housing 42 reaches its lower position with its lower surface against the surface of the transport member 130, the ejector piston 106 is lowered transmitting motion by means of the pins to the ejector member 112 which ejects the epoxy preform onto the top surface of the metal workpiece 48. When the upper die housing 42 is raised, the transport member 130 is moved out from underneath the upper die housing 42 and the metal workpiece with the epoxy preform attached thereto is removed from the cavity 150 either by hand, a pick-and-place mechanism, or other suitable mechanism and a new workpiece placed therein and the cycle repeated. In the embodiment shown in Figure 4, instead of a transport member that reciprocates inwardly and outwardly to feed the workpiece 48 underneath the upper die housing 42, a rotatable table member 170 having three arms 172 is provided which is rotatable about a center axis 173. Multiple cavities 177 for receiving the metal workpiece are provided in each arm 172. In the particular case shown in Figure 2, there are two such cavities 177 spaced in side-by-side relationship. In the case of this embodiment, the upper 174 and lower die housing of the punch and die assembly 176 are similar to those of Figure 2 except that they are provided with means for simultaneously forming two epoxy preforms and then ejecting them. Thus, the upper die housing 174 will contain two cavities and two ejectors and the lower die housing will contain two punches each mating with a respective cavity in the upper die housing. The table 170 is rotatably indexed (by suitable means not shown) from a position where two of the arms 172 are spaced on either side of the upper and lower die housings of the punch and die assembly 176 such that the upper die housing 174 can be moved downwardly to punch the preforms from the epoxy strip 50 positioned against the lower die housing. The third arm 172 extends radially outward from the punch and die assembly 176 and is positioned at Station A where the metal workpiece 48 are loaded into suitable cavities 177 in the of the outer portions of the arm 172. A cover-type stocker or other suitable mechanism 179 may be utilized to load the workpieces. As in the first embodiment, the epoxy preform, after being stamped from the strip 50, is maintained in a cavity in the upper die housing 174 as it is raised upwardly at which point the table is indexed such that an arm 172 containing a metal workpiece 48 is positioned underneath the upper die housing 174 so that the epoxy preform is deposited on the metal workpiece 48 upon the next downward movement of the upper die housing 174 and the actuation of the ejector member in a manner similar to that explained in connection with the embodiment of Figure 2. With the arrangement shown in Figure 4, it is possible to preheat the metal workpieces at Stations B and C by a suitable heater prior to their being positioned underneath the die assembly and the epoxy preform positioned thereon. After the preforms are deposited on the workpiece, the table 170 is then indexed again, moving the arm having the workpieces 50 with the epoxy preforms thereon to a position to the side of the upper and lower die housing 174 and 176 whereupon the strip 50 may be indexed and the upper die housing lowered to form a new preform. . Upon the next indexing, the arm 172 with the workpiece 48 having the preforms thereon are moved to Station D where they may be removed by a suitable mechanism, such as a pick-and-place mechanism 180 while new preforms are being deposited on the workpiece in the arm 172 positioned underneath the upper die assembly 174. While the invention has been described above with reference to specified embodiments thereof, it is apparent that many changes, modifications and variations can be made without departing from the inventive concept disclosed herein. Accordingly, it is intended to embrace all such changes, modifications and variations that fall within the spirit and broad scope of the appended claims.

Claims: WHAT IS CLAIMED IS; 1. An apparatus 40 for forming and positioning a preform 58 on a workpiece characterized by: (a) an upper and lower die 42, 44 housing having relative movement toward and away from each other for forming a preform 58 from a strip 50 upon movement of said upper and lower die housing toward each other and maintaining the preform in the upper die housing as the upper die housing is moved away from the lower die housing, (b) a transport means 46 for moving a workpiece into a position beneath the upper die housing 42 after a preform has been formed, and (c) means for transferring said preform 58 in said upper die housing 42 onto said workpiece 48 when said transport means has moved said workpiece into said position beneath said upper die housing. 2. The apparatus of claim 1 characterized in that said lower die housing 44 contains a punch 56 for stamping said preform 58 from said strip and said upper die housing contains a cavity 122 for receiving said preform which is punched from said strip 50. 3. The apparatus of claim 2 characterized by further including an ejector member 112 mounted in said upper die housing 42 and actuatable when said transport means 46 has moved a workpiece 48 underneath said upper die housing and said upper die housing is moved downward toward said lower die housing 44 to eject a preform 58 from said cavity 122 against said workpiece. 4. The apparatus of claim 1 characterized in that said means 46 for transporting said workpiece includes a transfer member 130 having a cavity 150 therein for receiving a workpiece 48 and reciprocal into and out of a position in which said workpiece receiving cavity is positioned below said upper die housing 42. 5. The apparatus of claim 1 characterized in that said means 46 for transporting said workpiece 48 includes a rotatable member 170 having a plurality of arms 172 extending radially outwardly from an axis of rotation thereof, at least one workpiece receiving cavity 177 in each of said arms adjacent an outer end thereof, said rotatable member 170 being rotatable from a position wherein said arms are positioned remote from said upper die housing 42 to a position wherein one of said arms 172 is positioned such that the cavity 177 is positioned underneath the upper die housing 42. 6. The apparatus of claim 1 characterized in that said preform 58 is an epoxy adhesive and said workpiece 48 is metallic. 7. The apparatus of claim 5 characterized in that there are a plurality of workpiece receiving cavities 177 in each arm. 8. A process for forming and positioning a preform 58 onto a workpiece 48 characterized by: forming a preform 58 from a strip 50 by punching said preform from said strip by movement of an upper die housing 42 toward a lower die housing 44, maintaining said punched preform in a cavity of said upper die housing as said upper die housing is moved relatively away from said lower die housing, moving a workpiece 48 into a position below said upper die housing after said preform has been formed, and transferring said preform onto said workpiece when said workpiece is positioned underneath said upper die housing. 9. The process of claim 8 characterized in that said preform 58 is an epoxy adhesive and said workpiece 48 is metallic. 10. The process of claim 8 further characterized by moving said workpiece 48 into and out of its position underneath said upper die housing 42 by movement in a linear direction. 11. The process of claim 8 further characterized by moving said workpiece 48 into and out of its position underneath said upper die housing 42 by arcuate movement by rotation about an axis spaced from said cavity 122. 12. The process of claim 8 further characterized by forming a plurality of preforms 58 at one time and simultaneously transferring said plurality of preforms onto said workpiece. AMENDED CLAIMS [received by the International Bureau on 13 October 1992 (13.10.92 ) ; original claims 1-12 replaced by amended claims 1-15 (4 pages)] 1. An apparatus 40 for forming and positioning a preform 58 on a workpiece 48 characterized by: a) First and second die housings 42,44 having relative movement toward and away from each other for forming a preform 58 from a strip 50 upon movement of said first and second die housing toward each other and maintaining the preform in the first die housing as the first die housing is moved away from the second die housing. b) A transport means 130 for moving a workpiece 48 into a preform receiving position between the first and second die housings 42,44 after a preform 58 has been formed, and c) Means 106,112 for transferring said preform in said first die housing 42 onto said workpiece 48 when said transport means 130 has moved said workpiece 48 into said preform receiving position. 2. The apparatus of claim 1 characterized in that one of said die housing 44 contains a punch 56 for stamping said preform 58 from said strip 50 and said first die housing 42 contains a cavity 122 for receiving the stamped preform 58. 3. The apparatus of claim 2 characterized by further including an ejector member 112 mounted in the cavity-containing die housing 42 and actuatable when the \ 7 workpiece 48 is positioned in the preform receiving position and the cavity-containing die housing 42 is moved toward the other die housing 44 to eject a preform 58 from said cavity 122 against said workpiece 48. 4. The apparatus of claim 1 characterized in that said means 46 for transporting said workpiece 48 includes a transfer member 130 having a cavity 150 therein for receiving a workpiece 48 and reciprocal into and out of the preform receiving position between the first and second die housings 42,44. 5. The apparatus of claim 1 characterized in that said means 46 for transporting said workpiece 48 includes a rotatable member 170 having a plurality of arms 172 extending radially outwardly from an axis of rotation thereof, at least one workpiece receiving cavity 177 in each of said arms adjacent an outer end thereof, said rotatable member 170 being rotatable from a position wherein said arms are positioned remote from said first die housing 42 to a position wherein one of said arms 172 is positioned such that the cavity 177 is positioned between the first and second die housings 42,44. 6. The apparatus of claim 1 characterized in that said preform 58 is an epoxy adhesive and said workpiece 48 is metallic. 7. The apparatus of claim 5 characterized in that there are a plurality of workpeice receiving cavities 177 in each arm 172. 8. A process for forming and positioning a preform 58 onto a workpiece 48 comprising: forming a preform 58 from a strip 50 by punching said preform from said strip by movement of a first die housing 42 toward a second die housing 44, maintaining said cut preform 58 in said first die housing 42 as said first die housing is moved relatively away from said second die housing 44 , moving a workpiece 48 into a preform receiving position between said first and second die housings 42,44 after said preform 58 has been formed, and transferring said preform 58 onto said workpiece 48 when said workpiece is in the preform receiving position between the first and second die housings 42,44. 9. The process of claim 8 characterized in that said preform 58 is an epoxy adhesive and said workpiece is metallic. 10. The process of claim 8 characterized in that said first die housing 42 is disposed above the second die housing 44 during the formation of the preform and during the transfer of the preform onto the workpiece 48. 11. The process of claim 8 characterized in that said moving step includes rotating said workpiece 48 about an axis spaced from said workpiece into and out of its preform receiving position between the first and second die housings 42,44. 12. The process of claim 8 characterized in that said forming step comprises simultaneously forming a plurality of preforms 58, and said transferring step comprises simultaneously transferring a plurality of preforms onto said workpiece 48. 13. The process of claim 8 characterized in that the transferring step further includes transferring the preform onto the workpiece when the workpiece is in a preform receiving position between the strip 50 and the first die housing 42. 14. The process of claim 8 characterized in that the transferring step further includes transferring the preform 48 onto the workpiece 58 while the mechansim 46 used to move the workpiece 58 during the moving step rests on one of the die housings 42,44. 15. The process of claim 14 characterized in that the process is performed entirely while the first die housing 42 is positioned above the second die housing 44.

Inventors: ROONEY JAMES, ROONEY, JAMES
Applicants: OLIN CORP, OLIN CORPORATION
Application year: 1992
Main classification: B21D35
IPC codes: B21D28, B26F1, H01L23, H05K13