Resin plunging apparatus for molding resin to seal an electronic device

The present invention relates to a molding apparatus for molding resin to seal an electronic device, and more specifically to a resin plunging mechanism for the molding apparatus for plunging resin tablets into the molds in the molding apparatus.

FIGS. 1 and 2 show a molding apparatus for molding resin to seal an electronic device, for example, an IC according to U.S. Pat. No. 5,435,953. This structure of molding apparatus comprises a plurality of plungers 12 a moved in and out of cavities 14 a and 15 a in stationary upper mold 10 a and movable lower mold 11 a . The plungers 12 a each have a plunger head 13 a . When the plungers 12 a are moved into the cavities 14 a and 15 a in stationary upper mold 10 a and movable lower mold 11 a , resin tablets 16 a are plunged into the molds 10 a and 11 a . The molding apparatus further comprises two load elements 17 a driven by a motor 18 a through a respective belt transmission mechanism 19 a and a transmission rod 22 a to move two worm gear and worm mechanisms 20 a , causing the worm and worm gear mechanisms 20 a to move plunger holder means 21 a and the plungers 12 a up and down. This plunging mechanism is complicated. Pitch error and deformation of the worm gear and worm mechanisms 20 a and the belt transmission mechanism 19 a affects the movement of the plunger holder means 21 a , causing the plunger heads 13 a unable to be synchronously moved into the cavities 14 a and 15 a in the molds 10 a and 11 a , therefore the plunger heads 13 a tend to be damaged. Furthermore, during the operation of the molding apparatus, heat (molding temperature is as high as 170° C.) is transferred from the molds 10 a and 11 a through plunger holder means 21 a to the load elements 17 a and guide bars 33 a causing the load elements 17 a and guide bars 33 a to deform (because the worm and worm gear mechanisms 20 a and guide bars 33 a are securely limited on the movable plate 23 a , and no horizontal gap is left between the mechanisms 20 a and guide bars 33 a and the movable plate 23 a to absorb the space expansion of the load elements 17 a and the guide bar 33 a ). When the load elements 17 a deform, the plungers 12 a are forced to tilt in different directions, and the electronic device molding quality is affected. So the plunger heads 13 a are damged easily.

The present invention provides a plunging mechanism for a molding apparatus which eliminates the aforesaid drawbacks. In the plunging mechanism according to the present invention, a ball screw is rotated to move a movable base plate and two load elements at the movable base plate, enabling a plunger holder which is supported on the load elements to be moved with the movable base plate along guide bars, so that plungers which are securely mounted on the plunger holder are positively forced into cavities in upper and lower molds to plunge resin tablets.

FIG. 1 is a sectional view of a molding apparatus according to the prior art.

FIG. 2 is another sectional view of the prior art molding apparatus, showing resin tablets plunged into the cavities in the molds.

FIG. 3 is a front view of the prior art molding apparatus.

FIG. 4 is a bottom view of the prior art molding apparatus.

FIG. 5 is a front view of a molding apparatus according to the present invention.

FIG. 6 is a front view of the plunging mechanism for the molding apparatus shown in FIG. 5 .

FIG. 7 is a side view of the plunging mechanism shown in FIG. 6 .

FIG. 8 is a top view of the plunging mechanism shown in FIG. 6 .

FIG. 9 is a bottom view of the plunging mechanism shown in FIG. 6 .

Referring to FIGS. 5, 6 , 7 , 8 and 9 , an apparatus for molding a resin to seal an electronic device is shown comprised of a fixed top plate 10 , a fixed bottom plate 11 , a movable plate 12 , a clamping mechanism 13 driven to clamp and open the movable plate 12 vertically along four guide bars 16 between the top plate 10 and the bottom plate 11 , an upper mold 14 securely mounted on the bottom side wall of the top plate 10 , load plate 17 securely mounted on the top side wall of movable plate 12 , a lower mold 15 securely mounted on the top side wall of the load plate 17 and moved with the load plate 17 and the movable plate 12 relative to the upper mold 14 . When the clamping mechanism 13 is operated, the movable plate 12 is moved upwards (or downwards), causing the lower mold 15 to be closed on (or opened from) the upper mold 14 . The apparatus further comprises a resin plunging mechanism 20 controlled to plunge melted resin in the molds 14 and 15 .

The aforesaid resin plunging mechanism 20 comprises a plurality of guide bars 25 connected in parallel to the bottom side wall of the movable plate 12 , a movable base plate 21 moved up and down along the guide bars 25 , two load elements 22 securely mounted on the movable base plate 21 , a plunger holder 23 , a plurality of plungers 24 securely mounted on the plunger holder 23 , each plunger 24 having a front end terminating in a plunger head 32 , a ball guide screw 31 connected to the center of the movable base plate 21 , a nut 26 threaded onto the guide screw 31 , a reversible motor 27 disposed below the movable plate 12 , a driving pulley 28 securely mounted on the output shaft of the reversible motor 27 , a follow up pulley 29 securely mounted on the nut 26 , and a timing belt 30 mounted on the pulleys 28 and 29 .

A movable guide bar 33 is securely mounted on the plunger holder 23 at the bottom side, and moved in an oilless bearing 39 . The oilless bearing 39 is mounted in the movable plate 12 . When the plunger holder 23 is moved up and down, it is guided by the guide bar 33 . An upper limit switch 36 , a lower limit switch 37 and a sensor 38 are disposed at one side relative to the plunger holder 23 to control moving distance of the plunger holder 23 and the plungers 24 . Because the guide bar 33 is suspended at the center and the load elements 22 are inserted through respective through holes at the movable plate 12 with a gap left between the movable plate 12 and around the periphery of each load element 22 , the resin plunging mechanism has better heat expansion absorbing capability when the temperature of the plunger holder 23 is increased due to heating of the molds 14 and 15 , and strain gage 40 can be provided at the load elements 22 at a remote plate far away from the heat source.

When the reversible motor 27 is started to turn the pulleys 28 and 29 and the timing belt 30 , the nut 26 is rotated with the pulley 29 , thereby causing the ball screw 31 to be moved upwards or downwards. When the ball screw 31 is moved upwards, the resin tablets which are carried on the plunger heads 32 of the plungers 24 are plunged into cavities in the molds 14 and 15 , enabling resin tablets to be melted and sealed to the electronic device. Further, the ball screw 31 can be replaced with a linear motor, hydraulic cylinder, or pneumatic cylinder, and the belt transmission mechanism can be replaced with a gear transmission mechanism or chain transmission mechanism.

As indicated above, the present invention uses a ball screw 31 and a movable base plate 21 to carry two load elements 22 up and down. Because the load elements 22 are securely connected to the movable base plate 21 , the load elements 22 are synchronously moved with the movable base plate 21 . Because the movable base plate 21 is moved along the guide bars 25 , the movement of the movable base plate 21 is smooth and stable. Because the guide bar 33 is securely connected to the plunger holder 23 and moved with the plunger holder 23 in the oilless bearing 39 , the plungers 24 are positively synchronously moved into the cavities in the molds 14 and 15 , preventing the plunger heads 32 from damage.

It is to be understood that the drawings are designed for purposes of illustration only, and are not intended as a definition of the limits and scope of the invention disclosed.