Package for electrical components having a molded structure with a port extending into the molded structure

A package for mounting electrical components and a method for making the package. A mold structure (50) is formed by encapsulating a portion of a leadframe (10) with a molding compound. Leads (23) project from one side of the mold structure and a portion of a tab (27) projects from another side of the mold structure, which has a cavity (57) between the leads (23) and the tab (27). In addition, the mold structure has vent holes (76) between the leads (23) and an aperture (62) extending to the cavity. After mounting a semiconductor chip (64) in the cavity (57), it is covered by a lid (53) and a portion (24) of the leads (23) and a portion (29) of the tab (27) are formed. The tab (27) provides structural rigidity to the mold structure (50) and permits surface mounting the mold structure (50).

BACKGROUND OF THE INVENTION 
The present invention relates, in general, to a package, and more 
particularly, to a package for an electrical component. 
Packaging electrical components entails a multitude of processing steps 
that are tailored to the type of electrical component being packaged and 
the type of package desired. For example, steps for packaging a 
semiconductor chip in a single-in-line package typically include: mounting 
the semiconductor chip to a leadframe, coupling bonding pads on the 
semiconductor chip with corresponding leadframe leads, encapsulating the 
semiconductor chip and a portion of the leadframe with a molding compound, 
and trimming and forming the leadframe. A pressure sensing integrated 
device, on the other hand, is typically packaged in a single-in-line 
package by mounting it to a molded structure, coupling bonding pads on the 
pressure sensing integrated device with corresponding leadframe leads, 
securing a cap to the molded structure, and trimming and forming the 
leads. Although single-in-line packages are useful for packaging 
electronic components, they are difficult to mount on substrates such as 
printed circuit boards using techniques such as infra red (IR) reflow 
soldering techniques. 
Accordingly, it would be advantageous to have a method and a means for 
packaging an electronic component that enables mounting the electronic 
component to printed circuit boards using IR reflow solder techniques. It 
would be of further advantage for the package to be suitable for packaging 
active components such as sensors and passive components such as 
capacitors.

DETAILED DESCRIPTION OF THE DRAWINGS 
Generally, the present invention provides a method and a means for 
packaging active and passive electrical components such as integrated 
devices and capacitors, respectively. In accordance with the present 
invention, a package is fabricated having leads extending from one side of 
the package and a tab extending from another side of the package. 
Preferably the tab is electrically isolated from the leads. The tab makes 
possible surface mounting electrical components packaged in single-in-line 
packages. 
FIG. 1 illustrates a top view of a portion of a semiconductor leadframe 10 
comprising three individual leadframe configurations, wherein each 
leadframe configuration represents a separate leadframe embodiment. As 
those skilled in the art are aware, a single semiconductor leadframe 
typically comprises a single leadframe embodiment having a plurality of 
portions held together by tie strips and a connecting band. After 
encapsulation, the leadframe is separated or singulated into individual 
portions. However, it should be understood that the three leadframe 
embodiments have been combined into a single leadframe 10 in FIG. 1 to 
facilitate a description of the present invention. 
A first embodiment of a leadframe of the present invention is shown in the 
left-hand portion of semiconductor leadframe 10, hereby defined herein as 
first leadframe portion 13. Likewise, a second embodiment of a leadframe 
of the present invention is shown in a middle portion of semiconductor 
leadframe 10 which is hereby defined herein as second leadframe portion 
14. Further, a third embodiment of a leadframe of the present invention is 
shown in the right-hand portion of semiconductor leadframe 10 which is 
hereby defined herein as third leadframe portion 17. Leadframe portions 
13, 14, and 17 are held together by a connecting band 18, a dam bar 19, a 
dam bar 21, and tie strips 22. Connecting band 18 and dam bars 19 and 21 
are substantially parallel to one another and tie strips 22 are 
substantially perpendicular to connecting band 18 and dam bars 19 and 21. 
However, it should be understood that the spatial relationship of 
connecting band 18, dam bars 19 and 21, and tie strips 22 is not a 
limitation of the present invention. In addition, either connecting band 
18, or tie strips 22, or their junction points have indexing holes 30 
which are used to move or index the leadframe during the steps of forming 
a package and packaging an electronic component. 
First leadframe portion 13 comprises two substantially parallel tie strips 
22 coupled at three locations by conducting band 18 and dam bars 19 and 
21. More particularly, tie strips 22 are coupled at one end by conducting 
band 18, at one end by dam bar 21 and at a central position by dam bar 19. 
A plurality of leads 23 having first and second ends 24 and 26, 
respectively, extend through dam bar 19. First ends 24 are coupled to 
second ends 26 by central portions. First ends 24 serve as surface mount 
bonding ends and second ends 26 serve as interconnect bonding ends. 
Although six leads are shown in first leadframe portion 13, it should be 
understood that the number of leads is not a limitation of the present 
invention and that the present invention is applicable to inventions 
having more or less than six leads. 
The intersection or junction of two adjacent leads with dam bar 19 forms a 
first corner 20 and a second corner 25 with the portion of the dam bar 
which is between these two adjacent leads. In other words, corner 20 is 
formed by a junction of a first of the two adjacent leads of the plurality 
of leads with a portion of dam bar 19 which is between the two adjacent 
leads and corner 25 is formed by a junction of a second of the two 
adjacent leads with another portion of the dam bar which is between the 
two adjacent leads. 
Dam bar 21 comprises a first or wide portion 21' and a second or narrow 
portion 21". A tab 27 having first and second ends 28 and 29, 
respectively, extends through narrow portion 21". First end 28 serves as a 
fastening end and second end 29 serves as a surface mount bonding end. A 
corner 37 is formed at an intersection of wide portion 21' and narrow 
portion 21". In addition, a corner 38 is formed at an intersection of tab 
27 and narrow portion 21". Tab 27 having ends 28 and 29 will be further 
described with reference to FIGS. 2-4. Techniques for manufacturing first 
leadframe portion 13 are well known to those skilled in the art. 
After manufacturing first leadframe portion 13, a portion of tab 27 
adjacent end 28 is coined or formed to have a bend. By way of example, the 
bend forms an angle of approximately ninety degrees; however, the angle of 
the bend is not a limitation of the present invention. The bend is 
illustrated by dashed line 31. In addition, a portion of tab 27 adjacent 
end 29 is coined or formed to have an L-shape. Dashed lines 32 indicate 
the portions of tab 27 that are coined to have bends that form the 
L-shape. Techniques for coining or forming portions of a leadframe are 
well known to those skilled in the art. 
FIG. 2 illustrates a cross-sectional view (through section lines 2--2 of 
FIG. 1) of first leadframe portion 13 after tab 27 has been coined. What 
is shown in FIG. 2 is a portion of connecting band 18, portions of tie 
strip 22, portions of ends 24 and 26 of a lead 23, a portion of dam bar 
19, and a portion of tab 27. More particularly, FIG. 2 shows tab 27 after 
it has been coined, thereby illustrating bend 33 adjacent end 28. It 
should be understood that the portion 34 of tab 27 may point in a downward 
direction as shown in FIG. 2 or in an upward direction (not shown), i.e., 
a direction opposite the direction shown in FIG. 2. In addition, L-shaped 
portion 36 adjacent end 29 is shown. By way of example, bend 33 and 
L-shaped portion 36 may be formed using a punch and die. 
Referring again to FIG. 1 and in accordance with a second embodiment of the 
present invention, dam bar 19 has two semicircular notches 39 between 
adjacent leads that are spaced apart from each other and extend into dam 
bar 19. One terminus of a radial line of one semicircular notch 39 is at 
corner 20 and one terminus of a radial line of another semicircular notch 
39 is at corner 25. Likewise, portion 21" of dam bar 21 has semicircular 
notches 41 that are spaced apart from each other and extend into dam bar 
21. One terminus of a radial line of one semicircular notch 41 is at 
corner 37 and one terminus of a radial line of another semicircular notch 
41 is at corner 38. Semicircular notches 39 may be made using a punch and 
die. Preferably, semicircular notches 39 and 41 are made simultaneously. 
Techniques for making semicircular notches 39 and 41 are well known to 
those skilled in the art and include piercing, notching, etc. 
In accordance with the third embodiment of the present invention, second 
leadframe portion 17 has two slits 42 spaced apart from each other and 
between adjacent leads. Slits 42 extend a desired distance into a portion 
of dam bar 19 between corners 20 and 25. Likewise, portion 21" of dam bar 
21 has slits 43 spaced apart from each other and extending into dam bar 
21. By way of example, slits 42 make an angle of approximately 90 degrees 
with an edge of dam bar 19 and slits 43 make an angle of approximately 90 
degrees with an edge of dam bar 21. It should be understood that the angle 
slits 42 and 43 make with the edges of dam bars 19 and 21, respectively, 
is not a limitation of the present invention. It should be noted that 
notches 39 and 41 and slits 42 and 43 serve to prevent burr formation 
during a dam bar removal step. 
FIG. 3 illustrates a cross-sectional view of a portion of an embodiment of 
a sensor package 50 comprising first leadframe portion 13. First leadframe 
portion 13 is placed in a mold (not shown) and a molding compound is 
injected into the mold to form a molded structure or body 51. Molded 
structure 51 comprises a top side 52 having a lid 53 and a bottom side 54 
having a nipple 56. Further, the mold is shaped so that the molding 
compound encases the central portion of leads 23 and portion 34 of tab 27. 
In other words, a portion of molded structure 51 is bonded to the central 
portion of leads 23 and to portion 34 of tab 27. Portion 34 serves to 
secure tab 27 in molded structure 51. In addition, molded structure 51 
comprises a cavity 57 having a floor 58, sidewalls 59 and a ledge 61. Ends 
26 of leads 23 rest on ledge 61. Further, portions of ledge 61 between 
ends 26 have vent holes 76 extending through bottom side 54 (shown in FIG. 
4). As those skilled in the art are aware, vent holes 76 permit an ambient 
environment surrounding sensor package 50 to enter cavity 57. 
An aperture 62 extends from a portion of floor 58 through molded structure 
51 to bottom 54. Aperture 62 is aligned with nipple 56. The portion of 
floor 58 containing aperture 62 serves as an electrical component 
receiving area 63. A semiconductor chip 64 is bonded to electrical 
component receiving area 63 with an adhesive 66. Preferably adhesive 66 is 
a silicone rubber adhesive that is heat curable, capable of being 
dispensed from a nozzle at room temperatures, bondable to a plastic 
package and a semiconductor chip, and capable of isolating stresses from 
the plastic package and the semiconductor chip. In accordance with the 
sensor embodiment, semiconductor chip 64 is a sensor element that is 
positioned to cover aperture 62. Accordingly, adhesive 66 preferably 
provides an air-tight seal between semiconductor chip 64 and floor 58. By 
way of example, semiconductor chip 64 is a pressure sensor having part 
number DXL4104BSP or DXL2300V1. 
Bonding pads 67 are coupled to corresponding ends 26 of leads 23 by metal 
wires 68, commonly referred to as wirebonds. Suitable materials for metal 
wires 68 include gold, copper, aluminum, and the like. 
Lid 53 is mounted to molded structure 51 to cover cavity 57. By way of 
example, lid 53 is a molded structure made from the same material as 
molded structure 51 and comprising a flat plate 71 having projections or 
feet 72. Lid 53 is press-fit onto molded structure 51 such that 
projections 72 mate fit snugly against corresponding sidewalls 59. 
Preferably, projections 72 adjacent sidewall 59 on the side of sensor 
package 50 having leads 23 are in contact with ends 26. Further, 
projections 72 adjacent sidewall 59 on the side of sensor package 50 
having tab 27 do not contact adhesive 66 or semiconductor chip 64. 
Alternatively, lid 53 may be ultrasonically welled to molded structure 51. 
FIG. 4 illustrates an exploded isometric view of the sensor package of FIG. 
3. What is shown in FIG. 4 is the sensor package 50 having a molded 
structure 51 and a lid 53. FIG. 4 further shows leads 23 and tab 27 
encased in molded structure 51 and L-shaped portions 36 and 73 of tab 27 
and leads 23, respectively. In addition, semiconductor chip 64 is coupled 
to floor 58 by adhesive 66 and covers aperture 62. Leads 23 are coupled to 
corresponding bonding pads on semiconductor chip 64 by wires 68. 
In addition, vent holes 76 are illustrated in molded structure 51. Although 
vents holes 76 are shown as being between adjacent leads 23, it should be 
understood this is not a limitation of the present invention. Other 
suitable locations for vent holes 76 include lid 53, sidewalls 59, and 
portions of floor 58 adjacent electrical component receiving area 63. 
A portion 73 of lead 23 adjacent end 24 is coined or formed to have an 
L-shape corresponding to the L-shaped portion 36 of tab 27. L-shaped 
portions 36 and 73 serve to contact bonding pads on, for example, printed 
circuit boards (not shown). The L-shape portion 36 of tab 27 in 
cooperation with the L-shaped portion 73 of lead 23 permit surface 
mounting sensor package 50 to, for example, a printed circuit board using 
such techniques as IR solder reflow. It should be understood that the 
L-shaped portions may face in an opposite to direction to that shown in 
FIG. 3. 
FIG. 4 further illustrates a nozzle 77 having a lip 78. Nozzle 77 is 
capable of mating with a hose (not shown) for delivering a medium to 
semiconductor chip 64. The medium exerts a pressure on the side of 
semiconductor chip 64 adjacent aperture 62. Subsequently, semiconductor 
chip 64 develops an electrical signal in accordance with the difference in 
pressure between cavity 57 and the side of semiconductor chip 64 adjacent 
aperture 62. Thus, sensor package 50 serves as a package for a pressure 
sensor. 
By now it should be appreciated that a method and means for manufacturing a 
package that can be surface mounted to a substrate, such as a printed 
circuit board, using techniques such as IR reflow soldering has been 
provided. In accordance with one embodiment of the present invention, a 
tab is molded into one side of a mold structure, wherein the tab is 
electrically isolated from leadframe leads. In addition, the tab provides 
structural rigidity for surface mounting the package. Further, the package 
includes vent holes, which may be between leads, through leads or in a 
central portion of the package. Optionally, the package includes a 
separate cap and port. A hose may be attached to the port, wherein the 
hose delivers a liquid to a pressure sensor within the package. 
While specific embodiments of the invention have been shown and described, 
further modifications and improvements will occur to those skilled in the 
art. It is understood that this invention is not limited to the particular 
forms shown and it is intended for the appended claims to cover all 
modifications of the invention which fall within the true spirit and scope 
of the invention. For example, the vent holes may be formed through the 
leads of the leadframe or the leadframe may include a flag.