Printed circuit board with integrated circuit devices mounted on both sides thereof

Abstract: Two flat packages (110,111) are arranged to achieve a mirrored footprint when mounted or opposite sides of a printed circuit board by employing guides (100), which are positioned within a mounting aperture the printed circuit board. The flat packages include leads (120,121) which end from the edge of the flat package. A semiconductor chip is encapsulated by the flat packages.

Description: Technical Field of the Invention This invention relates to semiconductors and, more particularly, to a surface-mounted integrated circuit structure of the type defined in the precharacterizing portion of the claim. Background of the Invention Integrated circuit devices have been housed in dual-in-line plastic packages, referred to as DIP packages, for many years in semiconducting manufacturer. These DIP packages have leads extending through holes in a printed circuit board, and the package itself is mounted flat on the board. More recently, surface-mount packaging has been introduced, and this technique eliminates the necessity of soldering leads in holes in the PC boards, so the leads and the PC board connectors can be closer together achieving higher densities. U.S. Patent 4,994,896 to Uemura et al. discloses a method of manufacturing a semiconductor device, wherein two types of semiconductor packages, being different in direction of bending of external lead terminals from each other, are prepared to be mounted on a single surface or both surfaces of a package substrate. In case of a single-surface mounting, the external lead terminals of the same pin numbers can be electrically connected with each other by drawing around wires. In case of double-surface mounting, the external lead terminals of the same pin numbers can be electrically connected with each other by through holes. U.S. Patent 5,061,990 to Arakawa et al. discloses a method of manufacturing a semiconductor device comprising coating a metal layer on each of the front and the rear surfaces of a tape, forming through holes which make conduction between the front surface and the rear surface, etching the metal layers to leave a plurality of connection terminals connected to the through holes and lead terminals each connected to at least one of the plurality of connection terminals, subjecting portions other than the connection terminals and the lead terminals to insulation treatment, and forming a metal coating on areas not provided with the insulation treatment, and forming a module including preparing a plurality of TAB-packaged IC devices having outer leads, and bonding the outer leads of the plurality of IC devices to the connection terminals to mount the IC devices on the tape, and cutting the module from the tape, and connecting the lead terminals to the terminals of a circuit board to mount the module on the circuit board. Similarly, edge-mounted packages or modules have been used in an effort to further increase the density of devices, improving cooling and reducing cost. U.S. patent 5,260,601 to Baudouin et al. discloses a pair of protruding studs or spacers, positioned on the same edge of a flat package as the leads. These studs or spacers are composed of molded plastic and are formed at the same time as the package itself. The spacers include a reduced-diameter cylindrical portion for insertion into holes in the printed circuit board where the device is to be mounted and include lip or stop portions co-planar with the flat surfaces of the leads so that the leads will be positioned for soldering to the conductors on the printed circuit board. An integrated circuit structure of the type defined in the precharacterizing portion of the claim is known from EP-A-0 427 151. Summary of the Invention The present invention provides an edge-mounted or surface mounted device with respect to the package or the printed circuit board. The present invention provides a device that can be packed with a very high packing density and achieves a low profile. The high packing density is achieved by packages being positioned on both sides of the printed circuit board, eliminating the need for two printed circuits boards. Additionally, the layout of the board is simplified because devices mirror each other by rotation. The present invention provides a surface mounted integrated surface structure as mentioned above and comprising the features of the characterizing portion of the claim. Description of the Drawings For a more complete understanding of the present invention and for further advantages thereof, reference is now made to the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 illustrates a plan view of a flat package which normally will be vertically surface mounted on edge with guides; Fig. 2 illustrates a sectional view of the flat package and an embodiment of the guides with the printed circuit board; Fig. 3 illustrates a perspective view of the flat package with guides and an aperture of the printed circuit board; Fig. 4 illustrates a top view of the mounting hole of the printed circuit board and guides with split and spring-formed style guides, shaped to allow interlocking guides to provide positive support; Fig. 5 illustrates a perspective view of a plurality of flat packages positioned on both sides of a printed circuit board; Fig. 6 illustrates a section view of the guides and PC board of the present invention with stud style guides, each extending one-half thickness into PC board; Fig. 7 illustrates a top view of guides within the mounting hole of the printed circuit board with formed angle style guides, shaped to allow guides to pass from either side of PC board with full thickness extention; Fig. 8 illustrates a top view of the guides within the mounting hole with split tab style guides, shaped to allow guides to interlock within PC board mounting hole; Fig. 9 illustrates a perspective view of the flat package and guides with split tab style guides, oriented to allow interlocking guides within PC board mounting hole; Fig. 10 illustrates a top view of additional guides within the mounting hole with formed angle style guides; and Fig. 11 illustrates a top view of further guides within the mounting hole. Detailed Description of the Invention As illustrated in Fig. 1, two flat packages 110, in for encapsulating an integrated circuit device (not shown) which is connected to the printed circuit board having a length, a width and a depth by the lead frames 120 by soldered connections 114 through via S to both devices (not shown). These lead frames 120 may be connected to bumps on the integrated circuit chip. Alternatively, the leads may be connected to bonding pads on the integrated circuit chip. The leads are properly aligned by guides in the apertures to provide for connection to the upright flat package 110 which is positioned with respect to the inverted flat package 111 such that a mirrored foot print of the lead frames 120 is obtained. The mirrored footprint is obtained by employing a printed circuit board having the same connection configuration on one side as the other side of the printed circuit board and having the same configuration of the pins in that a particular pin on the upright flat package 120 is opposite to the same pin on the inverted flat package 121. Fig. 2 further illustrates this aspect of the present invention in that connection 114 connects both leadframe 120 of the upright flat package 120 to connection 114 and leadframe 121 of the inverted flat package 111 to connection 114. Thus flat packages that may be positioned on the printed circuit board in accordance with this mirrored footprint resulting in a simple and inexpensive printed circuit board. Fig. 2 illustrates one arrangement of guides 100, which achieve the mirrored foot print. The guide 100 guides and secures the flat package 110 by wedging the guide 100 against the surface of the mounting aperture 130. These guides 100 are of such a length such that the flange 125 is a stop for the guide 100 by abutting the printed circuit board. The flange 125 is positioned on guide 100 such that the flange 125 stops the guide 100 in the aperture, preventing the guide 100 from abutting or overlapping with the guide of the opposing flat package 111. The flanges 125 are additionally positioned such that the lead frames 120 connect with the connection 125 of the printed circuit board. Fig. 6 illustrates that the guides 100 are positioned within the mounting aperture 130 in the printed circuit board and that the flange 125 abuts the printed circuit board, preventing the overlap of the guides in the printed circuit board. Fig. 3 illustrates another example, which is not covered by the scope of the claims, where the guides may be metal integral with the lead frame. In this example, the guides of the upright flat package 110 are of a sufficient length to abut and overlap the guides of the inverted flat package 111. The guides for example guides 102 and 104 are positioned to be parallel with respect to each other and the length of the flat package yet to be offset such that guide 102 is staggered with respect to guide 104. For example, the forward guide 102 of the inverted flat package is in a first plane while the rearward guide 104 of the inverted flat package is in a second plane. The first and second planes are substantially parallel for example within 10 degrees of each other. Additionally, the forward guide 106 and the rearward guide 108 are similarly parallel offset and staggered with respect to each other. This staggered positioning of forward and reverse guides for the inverted and upright flat package respectively achieves the mirrored footprint since any arrangement of the inverted and upright flat packages not achieving the mirrored footprint would result in the distal end of guides 102 and 104 of the inverted mounting package in the mounting aperature 130 abutting the distal end of the guides 106 and 108 of the upright mounting package, preventing the flange 125 from abutting the surface of the printed circuit board and the lead frames 120 from connecting with connections 114. The guides 102, 104, 106, 108 securely position the flat packages 110, 111 by wedging the guides 102, 104, 106, 108 against one another and against the surface of the mounting aperature 130 when the mirrored footprint has been achieved. Fig. 8 illustrates the guides 102, 104, 106 and 108 within the mounting aperature 130 of the printed circuit board 140. Since the length of each of these guides are greater than one-half the depth of the printed circuit board, the guides overlap and are staggered as illustrated. The upright and inverted flat package (Fig. 3) 110 and 111 include flange 125 to stop the guide within the mounting aperture 130. The flange 125 is positioned so that the lead frame 120 abuts the connection 114 of the printed circuit board to complete a connection with the printed circuit board. Additionally, the flange 125 when abutting the printed circuit board, positions the guides 102, 104, 106, 108 in the overlapped position. Fig. 4 illustrates another example which is not covered by the scope of the claims. The forward guide 202 for the inverted flat package may include an inclined portion 212 to abut an inclined portion 218 of the rearward guide 208 of the upright flat package. Likewise, the forward guide 206 abut of the upright flat package includes an inclined portion 216 to abut an inclined portion 214 of the guide 204 of the rearward flat package. The inclined portion 212 facilitates the abutment of the inclined portion 218 to securely wedge the guide against the surface of the mounting aperature. The inclined portion 216 facilitates the abutment of the inclined portion 214. As illustrated in Fig. 5, a plurality of flat packages may be mounted on one side of a printed circuit board 140 and a second plurality of flat packages may be mounted on the opposing side of the printed circuit board 140. This provides for an efficient and high density positioning of the flat packages. Fig. 7 illustrates another example which is not covered by the scope of the claims. Fig. 7 illustrates two L-shaped guides in mounting aperature 130. L-shaped guide 302 of the upright flat package abuts with the L-shape guide 304 of the inverted flat package. Both L-shaped guides 302 and 304 abuts with the surface of the mounting aperature to position and secure the flat package on the printed circuit board. Fig. 7 illustrates that guide 302 is smaller than guide 304. Fig. 10 illustrates that L-shaped guides 308 are of equal size to L-shaped guides 310. The use of the L-shape guides 302 and 304 does not assure that the mirrored footprint is achieved. Fig. 9 illustrates another example which is not covered by the scope of the claims. The flat package 110 includes two parallel guides 402 and two perpendicular guides 404. The parallel guides 402 are substantially parallel and in the same plane as the length of the flat package 110. Furthermore, the perpendicular guides 404 are substantially in the same plane but perpendicular to the length of the flat package. Fig. 11 additionally illustrates that the parallel guides 402 of the upright flat package abut the perpendicular guides 406 of the inverted flat package. Additionally, the perpendicular guides 404 of the upright package abut the parallel guide 408 of the inverted flat package. This does achieve the mirrored footprint. The above mentioned guides of the present invention may be integrated with the package or lead frame or formed with the flat package after manufacture. Other Embodiments Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims: A surface mounted integrated circuit structure comprising: a printed circuit board (140) having first and second opposing major sufaces, the printed circuit board having mounting apertures (130) formed in said surfaces; a first semiconductor integrated circuit device having a first flat package (110) encapsulating a first semiconductor chip, a plurality of first conductive leads (120) extending from one edge of said first flat package (110), first guides (100) extending from the said one edge of said first flat package (110) and shaped to fit into said apertures (130) in said first surface of said printed circuit board (140) for mechanically positioning and supporting said first flat package (110) when the, first conductive leads (120) are soldered to said printed circuit board (140); said first integrated circuit device being positioned such that said first conductive leads connect with connection portions (114) on said first surface of said printed circuit board; a second integrated circuit device having a second flat package (111) encapsulating a second semiconductor chip, a plurality of second conductive leads (121) extending from one edge of said second flat package (111), second guides (100) extending from the said one edge of the second flat package (111) and shaped to fit in said apertures in said second surface of said printed circuit board for mechanically positioning and supporting the package (111) when said second conductive leads (121) are soldered to said printed circuit board (140); said second integrated circuit device being positioned such that said second conductive leads connect with connection portions on said second surface of said printed circuit board; whereby said apertures extend through the printed circuit board; and the second guides (100) are shaped to fit into said same apertures (130) as said first guides (100); characterized in that said first and second guides (100) have a length such that the guides do not abut or overlap; and said first and second guides (100) are positioned in said mounting apertures (130) such that corresponding leads of said first and second conductive leads (120, 121) are opposite to each other and are interconnected by respective straight connections between said first and second surfaces of said printed circuit board.

Inventors: BAUDOUIN DANIEL, RUSSELL ERNEST, WALLACE JAMES S, BAUDOUIN, DANIEL, RUSSELL, ERNEST, WALLACE, JAMES S.
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1995
Main classification: H01L25
IPC codes: H01L23, H05K1, H01L25, H05K3