Patent Publication Number: US-2007095564-A1

Title: Thin printed circuit board

Description:
FIELD OF THE INVENTION  
      The present invention relates to the field of mounting chips on printed circuit boards.  
     BACKGROUND OF THE INVENTION  
      The term Integrated Circuit (IC) refers in the art as to a microelectronic semiconductor device consisting of many interconnected transistors and other electronic components. ICs are constructed on a small rectangle cut from a Silicon (or for special applications, Sapphire) wafer. Integrated circuits are also known as “Chips”.  
      The term Printed Circuit Board (PCB) refers in the art as to a printed board on which chips and other electronic components are placed.  
      The term Chip Mount Technology refers in the art as to a technology of electronic assembly manufacturing, such as TOB, COB or Flip chip, which connects bare integrated circuit to a printed board (substrate). There are several types of flip chip mounting methods, each one focused in a different aspect, such as low cost performance, high bonding temperature, bonding reliability, process flexibility, etc.  
      As the currently popular products, such as cellular telephones, PDAs, and laptop computers, get smaller, decreasing the thickness of a PCB becomes an essential issue. Nevertheless the methods of the prior art have not provided a satisfactory solution for decreasing the thickness of a PCB.  
      It is an object of the present invention to provide a PCB whose thickness is less than a prior art PCB which comprises the same chips.  
      It is another object of the present invention to provide technologies for manufacturing a PCB, whose thickness is less than a prior art PCB which comprises the same chips.  
      Other objects and advantages of the invention will become apparent as the description proceeds.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to a printed circuit board, comprising: at least one chip; and a board comprising at least one aperture corresponding to each chip, for enabling each chip to be placed inside the corresponding aperture, thereby enabling reducing the thickness of the printed circuit board to that of the thickest chip. According to one embodiment of the invention, the chip is placed on the board with the upper side of the chip up. According to another embodiment of the invention, the chip is placed on the board with the upper side of the chip down. According to one embodiment of the invention the legs of the chip have “straight” form. According to another embodiment of the invention the legs of the chip have “bent” form.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention may be better understood in conjunction with the following figures:  
       FIG. 1  illustrates a PCB, according to a preferred embodiment of the invention.  
       FIG. 2  is a “sliced” cross section of the board illustrated in  FIG. 1 .  
       FIG. 3  illustrates a cross section along the mounting region of chips  20  and  50  of  FIG. 1 .  
       FIG. 4  illustrates the PCB of  FIG. 1 , in an upside-down position.  
       FIG. 5  illustrates a cross section along the mounting region of chips  20  and  50  of  FIG. 1  in a three-dimensional view.  
       FIG. 6  illustrates a chip having a “straight” form legs mounted on a board, according to the invention.  
       FIG. 7  illustrates a “bent” form legs mounted on a board, according to the invention.  
       FIG. 8  illustrates a “bent” form legs mounted on a board, according to another embodiment of the invention.  
    
    
     DETAILED DESCRIPTION OF PREFERED EMBODIMENTS  
       FIG. 1  illustrates a PCB, according to a preferred embodiment of the invention. Chips  10 ,  20 ,  30 ,  40 ,  50  and  60  are mounted on board  100 .  
      In order to facilitate the text to follow, it should be noted that the width corresponds to the X axis, the length corresponds to the Y axis, and the thickness corresponds to the Z axis of the board. Thus, the thickness of a PCB is actually the thickest point of the PCB (i.e. along the Z axis).  
       FIG. 2  is a “sliced” cross section of the board illustrated in  FIG. 1 . Apertures  11 ,  21 ,  31 , and  41  correspond to the chips  10 ,  20 ,  30  and  40 . Thus, when one of the chips  10  to  40  is mounted on the board  100 , the corresponding aperture enables to mount the chip such that the size of the outstanding part of a chip is diminished by the thickness of the board  100 .  
       FIGS. 3 and 4  illustrate a cross section along the mounting regions of chips  20  and  50 . Chip  50  is mounted according to the prior art, while chip  20  is mounted according to the present invention, i.e. into the aperture  21 . The thickness  102 , which is reflected from the fact that the chip  20  is inserted into the aperture  21 , is less than the thickness  102 .  
      The width and length of each aperture  11  to  41  is greater than the corresponding width and length of its corresponding chip, thereby allowing placing the chip inside the aperture. However, at least the width or the length of an aperture is smaller than the width or length of the corresponding chip including the chip&#39;s legs, thereby allowing the legs of the chips to contact the board  100 .  
       FIG. 6  illustrates a chip having a “straight” form legs mounted on a board, according to the invention. In  FIG. 6  the legs  42  of chip  40  are parallel to the board  100 .  
       FIG. 7  illustrates a “bent” form legs mounted on a board, according to the invention. The “bent” form of the legs is common in the chip industry.  
       FIG. 8  illustrates a “bent” form legs mounted on a board, according to another embodiment of the invention. The chip  20  is mounted in an upside-down position.  
      It should be noted that the legs of a chip may be manufactured to be flexible, thereby allowing mounting a chip on a board while pushing the chip towards the board, thereby bending its legs to the desired form.  
      Those skilled in the art will appreciate that the invention can be embodied in other forms and ways, without losing the scope of the invention. The embodiments described herein should be considered as illustrative and not restrictive.