Method of mounting electronic parts onto single-sided printed wiring board
This application is a continuation of application Ser. No. 835,752 filed on Mar. 3, 1986, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a system of mounting electronic parts onto a single-sided printing wiring board, and is particularly suitable for the manufacture of electronic equipment requiring key contacts, such as electronic calculators. 
     All conventional electronic equipment incorporating key contacts requires the key contact surface to be perfectly flat. To achieve this, manufacturers use a double-sided printed wiring board 1 as shown in FIG. 8, providing one of the surfaces 2 with a key contact pattern (not shown) and the other surface 3 with a variety of electronic parts 4. Both surfaces are electrically connected via through-holes 5. However, a double-sided printed wiring board 1 is relatively expensive. A single-sided printed wiring board as shown in FIG. 9 is more economical, but as the area peripheral to the key contact pattern 8 should be flat, such a board requires the key contact pattern area 8 to be separate from the electronic part mounting area 9. In consequence, a single-sided printed wiring board 7 is larger, going against today&#39;s trends towards miniaturization. 
     SUMMARY OF THE INVENTION 
     The present invention provides means for installing electronic parts onto a single-sided printed wiring board while keeping the area peripheral to the key contact pattern flat without any increase in board size, resulting in cost reductions. To summarize, the present invention is a single-sided printed wiring board to economically replace a double-sided one. 
     Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the following detailed description. 
     To achieve this, the present invention provides a system for mounting electronic parts onto a single-sided printed wiring board which has the key contact pattern on the front surface and a number of through-holes covered by a conductive pattern. Electronic parts are mounted into said through-holes from the rear surface of the printed wiring board. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and in which: 
     FIG. 1 is a flowchart describing the manufacturing procedure for a single-sided printed wiring board reflecting one of the preferred embodiments of the present invention; FIGS. 2(A), FIG. 3(A) and FIG. 4(A) are top plan views denoting the respective steps related to the manufacture of a single-sided printed wiring board reflecting one of the preferred embodiments of the present invention; 
     FIG. 2(B), FIG. 3(B), and FIG. 4(B) are sectional views denoting steps in the manufacture of such a single-sided printed wiring board; 
     FIG. 5 is a sectional view of the said single-sided printed wiring board reflecting one of the preferred embodiments of the present invention; 
     FIGS. 6 and 7 are sectional views of another preferred embodiment; and 
     FIG. 8 is a perspective view of a conventional double-sided printed wiring board. 
     FIG. 9 is a perspective view of a conventional double-sided and single-sided printed wiring board respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the production flowchart in FIG. 1, the procedure related to the manufacture of thin, single-sided printed wiring boards is described below. When first punching out base film substrate 11 made of glass epoxy resin, polymide resin, or polyester resin, etc. shown in FIG. 2(A) and (B), a specific number of through-holes 12 are simultaneously punched out to allow insertion of electronic parts. A copper foil 13 is next bonded over the prepared substrate 11 as shown in FIG. 3(A) and (B). Conductive patterns, including the wiring pattern, the key-contact pattern, and the part-insertion members (through-holes 12), are first masked on the cooper foil 13, etched, then masking materials are removed. Then, electrodeless gold plating is applied resulting in a single-side printed wiring board 21 shown in FIG. 4(A) and (B). 
     A conductive pattern 16 blocks through-hole(s) 12 on the front surface of board 21. On its front surface, this board 21 is provided with a number of conductive patterns 16 between key contact patterns 8 as shown in FIG. 5. Chip parts 24 are mounted on solder pads whose positions correspond to the through-holes 12 located on the rear surface where the positions of through-holes 12 respectively match the conductive patterns 16. Chip parts 24, are soldered to those conductive patterns 16, at the corresponding through-holes 12. 
     One of the preferred embodiments first provides a key-contact pattern 8, on the front surface of the board 21 and enables chip parts 24 to be mounted from the rear surface in positions corresponding to through-holes 12 and then soldered to conductive patterns 16. This method allows the peripheral area of key-contact pattern 8 of a single-sided printed wiring board to be perfectly flat, inexpensive yet compact and produced economically. 
     FIG. 6 denotes another preferred embodiment of the present invention. If the external metallic panel 27 of a single-sided printed wiring board 21 is grounded, both the conductive pattern 16 and external metallic panel 27 are electrically connected to each other via coil spring 28 at through-hole 12 so that no external static charge can adversely affect the wiring board. Note that identical reference numerals are used in both FIGS. 5 and 6 for denoting identical components. 
     FIG. 7 denotes another preferred embodiment, in which chip parts 24, are mounted on both the front and rear surfaces of a single-sided printed wiring board 21. Although not shown, the preferred embodiment shown in FIG. 5 allows complicated wiring on the printed wiring board to be easily implemented by replacing the solder-side chip parts with jumper wires. In addition, it allows the entire unit to be compact. In addition to a base film substrate, any conventionally available solid substrate may also be used for the base substrate. Likewise, chip parts may also be replaced by standard parts. 
     As is clear from the foregoing detailed description, according to the present invention, electronics parts are mounted in specific positions corresponding to through-holes from the rear side of a single-sided printed wiring board having a key contact pattern on its front surface and a conductive pattern covering the through-holes. Manufacturers can correctly install electronic parts without increasing the area peripheral to the key contact pattern and by maintaining its flatness, thus realizing compact size and reduced cost. While only certain embodiments of the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as claimed.