Semiconductor device packaged in plastic and mold employable for production thereof

A semiconductor device packaged in a plastic package wherein the thickness of the plastic mold on the top surface of the semiconductor device chip is less than the height of the lead on the top surface of the semiconductor device chip and the top surface to the plastic mold filling the space between the leads is convex downward in an arc shape, and a metal mold employable for producing the semiconductor device packaged in a plastic package comprising a lower mold having a cavity in which a semiconductor device chip provided with a plurality of leads thereon, is placed during a molding process, and an upper mold having a lower surface having a plurality of longitudinal projections and recesses arranged in parallel to one anther, the cross section of the longitudinal projections and recesses produced along the lower surface of the upper mold being effective to cause longitudinal linear contact along the longitudinal projections and recesses, between the lower surface and the edges of the leads, during a molding process.

FIELD OF THE INVENTION 
This invention relates to an improvement applicable to a semiconductor 
device packaged in a plastic package and to a metal mold employable for 
producing the semiconductor device packaged in a plastic package. More 
specifically, this invention relates to an improvement applicable to a 
small outline nonlead package, the improvement being effective to enhance 
the reliability of a semiconductor device packaged in a plastic package, 
the advantage being realized be preventing the surface discharge from 
occurring between leads of the semiconductor device packaged in a plastic 
package and by preventing a burr of a resin or a plastic material from 
being produced on the edge of a lead during the molding process for 
producing a semiconductor device packaged in a plastic package. 
BACKGROUND OF THE INVENTION 
The package of a semiconductor device is classified into two, including a 
ceramic package and a plastic package. The former has a large magnitude of 
reliability and the latter has an advantage in the economic aspects. 
Insofar as semiconductor devices employed for an IC, a memory card or the 
like are concerned, a plastic package is predominantly employed, because 
the plastic package can be thin and small in size, in addition to that the 
cost thereof is fairly less expensive. 
Referring to FIGS. 1 through 5, the structure of an example of a small 
outline nonlead package available in the prior art and drawbacks involved 
with the structure will be briefed below. 
Referring to FIGS. 1 through 3, each of leads 5 arranged in parallel to one 
another on the top surface of a semiconductor device chip 3 are bonded 
with each of pads 4 employing an Au wire 7. The semiconductor device chip 
3 is molded with a resin, or a plastic material. As a result, the top and 
side surfaces of the semiconductor device chip 3 is covered by a resin 
mold 9. Since the external ends of the leads 5 are designed not to extend 
beyond the side surface of the molded resin 9, as is illustrated in FIGS. 
1 and 2 and since the bottom surface of the semiconductor device chip 3 is 
not covered by the resin mold 9, the semiconductor device packaged in the 
foregoing small outline nonlead package available in the prior art has an 
advantage that the horizontal area is small and the thickness is thin. 
Referring to FIGS.2 and 3, the top surface 5a of the lead 5 is flush with 
the top surface 9a of the resin mold 9. This caused three drawbacks for a 
semiconductor device packaged in the small outline nonlead package 
available in the prior art. The first drawback is a rather short 
insulation distance between the leads 5, causing rather large 
possibilities in which the neighboring leads 5 are short circuited. It is 
noted is that a straight line connecting two points represents the 
shortest distance between the two points. The second drawback is a 
tendency in which neighboring two leads 5 are readily short circuited by 
foreign materials 13 laid on the top surface 9a of the resin mold 9 in a 
manner to bridge the neighboring two leads 5, causing large possibilities 
in which the neighboring leads 5 are short circuited, as is illustrated in 
FIG. 4 which illustrates a side view of a semiconductor device packaged in 
a plastic package available in the prior art which is mounted on a printed 
board 11 in a face down position. The third drawback is a tendency in 
which a resin flows along the top surface 5a of the lead 5 to produce a 
burr 15 of the resin illustrated in FIG. 5, during a molding process. In 
the drawing, the reference numeral 9 indicates shows a resin mold. The 
resin burr 15 readily causes less conductivity for the leads 5 or large 
possibility in which the surface conductivity is reduced by the resin burr 
15 spreading on the top surface 5a of the lead 5. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of this invention is to provide a semiconductor device packaged 
in a plastic package, wherein insulation between the neighboring leads is 
improved, possibility of a foreign material accidentally laid between the 
neighboring leads causes some adverse results is made less, and 
possibility to produce a resin burr on the top surface of a lead is made 
less. 
Another object of this invention is to provide a metal mold employable for 
producing a semiconductor device packaged in a plastic package, wherein at 
least one of insulation between the neighboring leads is improved, 
possibility of a foreign material accidentally laid between the 
neighboring leads causes some adverse results is made less, and 
possibility to produce a resin burr on the top surface of a lead is made 
less. 
To achieve at least one of the foregoing objects and other objects of this 
invention, a semiconductor device packaged in a plastic package in 
accordance with this invention includes: 
a semiconductor device chip, 
a plurality of leads each of which is bonded with reach of pads of the 
semiconductor device chip and arranged on the top surface of the 
semiconductor device chip in parallel to one another to extend towards the 
both opposite directions, extension of the ends of the leads beyond the 
edge of the semiconductor device chip being limited to a small length, and 
a resin mold covering the top and side surfaces of the semiconductor device 
chip, 
wherein the thickness of the resin mold on the top surface of the 
semiconductor device chip is less than the height of the lead on the top 
surface of the semiconductor device chip and the top surface of the resin 
mold filling the space between the leads is convex downward in an arc 
shape. 
In the foregoing semiconductor device packaged in a plastic package in 
accordance with this invention, the plastic package can be a small outline 
nonlead package. 
To achieve the foregoing other object of this invention, a metal mold 
comprising: 
a lower mold having a cavity in which a semiconductor device chip provided 
with a plurality of leads thereon arranged in parallel to one another to 
extend towards the both opposite directions, is placed during a molding 
process, and 
an upper mold having a lower surface having a plurality of longitudinal 
projections and recesses arranged in parallel to one anther, the cross 
section of the longitudinal projections and recesses has a wavy shape, 
resultantly the shape of the longitudinal projections and recesses 
produced along the lower surface of the upper mold being effective to 
cause longitudinal linear contact along the longitudinal projections and 
recesses, between the lower surface and the edges of the leads, during a 
molding process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to drawings, a detailed description will be presented below for a 
semiconductor device packaged in a plastic package in accordance with one 
embodiment of this invention and a metal mold employable for producing a 
semiconductor device packaged in a plastic package in accordance with one 
embodiment of this invention. 
Referring to FIG. 6, each lead 25 is arranged on the top surface of a 
semiconductor device chip 23 in parallel to one another. Each of the leads 
25 is bonded with each of contact pads 24 employing an Au wire 27. The 
semiconductor device chip 23 is molded with a resin, and the top and side 
surfaces of the semiconductor device chip 23 are covered by a resin mold 
29. It is important that the horizontal area of the resin mold 29 is not 
so much larger than that of the semiconductor device chip 23 and that the 
ends of the leads 25 do not exceed so much the side surface of the resin 
mold 29. It is effective to reduce the horizontal dimension and the 
thickness of the finished semiconductor device packaged in a plastic mold. 
It is noted that the height of the top surface 29a of the resin mold 29 is 
lower than the top surface 25a of the leads 25. 
Referring to FIG. 7, the top surface 29a of the resin mold 29 in the region 
between the leads 25 is convex downward to make a longitudinal recess 31 
extending along the leads 25. The depth of the longitudinal recess 31 is 
approximately a half of the height of the leads 25. The shape of the 
surface 29a of the resin mold 29 in the longitudinal recess 31 is 
preferably an arc or a part of a circle. Alternatively, the shape of the 
surface 29a of the resin mold 29 in the longitudinal recess 31 can be a 
V-shape. The top surfaces 25a of the leads 25 are flush with each other, 
allowing the longitudinal recess 31 to intervene therebetween. 
As was described above, the longitudinal recesses 31 having an arc shaped 
cross section intervene between the leads 25 of the semiconductor device 
of this invention. This is effective to make the distance between the 
leads 25 along the surface 29a of the resin mold 29, longer than that of 
the semiconductor device available in the prior art in which the surface 
of the resin mold is flush with the surface of a lead. In other words, the 
insulation distance along the surface 29a between the leads 25 is longer 
for the semiconductor device of this invention than for the semiconductor 
device available in the prior art. 
Further, the surface 29a of the resin mold 29 of the semiconductor device 
of this invention is remote from the surface 25a of the lead 25 of the 
semiconductor device of this invention. In this sense, a larger insulation 
space is secured between the leads 25. 
As a result, a leak current is effectively prevented from occurring between 
the leads 25, even a foreign material is accidentally laid between the 
leads 25 during a process in which the semiconductor device is mounted or 
after the semiconductor device is mounted. 
The longitudinal recess 31 produced between the leads 25 causes the surface 
29a of the resin mold 29 to be non-flat, resultantly preventing resin 
burrs 15 (See FIG. 5.) from being produced on the surface 25a of the lead 
25. This is effective to secure the surface conductivity of leads 25. 
Referring to FIGS. 8 and 9, the structure of a pair of metal molds 41 and a 
process for producing a semiconductor device packaged in a plastic package 
in accordance with this invention will be described below. FIG. 8 is a 
cross section of a pair of metal molds 41 in accordance with this 
invention and FIG. 9 is a cross section of the same, observing FIG. 8 in 
the direction shown by C--C therein. The pair of metal molds 41 consists 
of an upper mold 45 and a lower mold 43. The lower mold 43 has a cavity 47 
in which a semiconductor device chip 23 provided plural leads 25 is placed 
during a period in which a molding process is conducted, to be molded by a 
thermosetting resin. The semiconductor device chip 23 is placed in the 
cavity 47 in the upright position. 
Referring to FIGS. 8 and 9, the lower surface 49 of the upper metal mold 45 
has a plurality of longitudinal projections and recesses 51 arranged in 
parallel to one another having a cross section of a wavy shape. The wavy 
shape is preferably a continuation of portions of a circle. 
When a molding process is conducted, the semiconductor device chip 23 is 
placed in a manner that each of recesses 51a of the longitudinal 
projections and recesses 51 face each of the leads 25 and each of 
projections 51b of the longitudinal projections and recesses 51 face each 
of the space between the leads 25. Since the lower surface 49 of the upper 
mold 45 and the edges of the leads 25 contact in a longitudinal linear 
contact, a resin can not enter into spaces corresponding to the recesses 
51a, while spaces between the leads 25 are filled by the resin, and the 
top surfaces 29a (See FIG. 7.) of the resin mold 29 (See FIG. 7.) filling 
the spaces between the leads 25 become convex downward in an arc shape 
(See FIG. 7.). 
In this manner, a semiconductor device packaged in a plastic package 
wherein the thickness of the resin mold on the top surface of the 
semiconductor device chip is less than the height of the lead on the top 
surface of the semiconductor device chip and the top surface of the resin 
mold filling the space between the leads is convex downward in an arc 
shape can readily be produced by employing the foregoing metal mold. 
The forgoing description has clarified that this invention has successfully 
provided a semiconductor device packaged in a plastic package, wherein 
insulation between the neighboring leads is improved, possibility of a 
foreign material accidentally laid between the neighboring leads causes 
some adverse results is made less, and possibility to produce a resin burr 
on the top surface of a lead is made less and a metal mold employable for 
producing a semiconductor device packaged in a plastic package, wherein 
insulation between the neighboring leads is improved, possibility of a 
foreign material accidentally laid between the neighboring leads causes 
some adverse results is made less, and possibility to produce a resin burr 
on the top surface of a lead is made less. 
Although this invention has been described with reference to specific 
embodiments, this description is not meant to be construed in a limiting 
sense. Various modifications of the disclosed embodiments, as well as 
other embodiments of this invention will be apparent to persons skilled in 
the art upon reference to the description of this invention. It is 
therefore contemplated that the appended claims will cover any such 
modifications or embodiments as fall within the true scope of this 
invention.