Dummy core restrict resin process and structure

Abstract

A printed circuit board (PCB) has multiple layers, where select portions of inner layer circuitry, referred to as inner core circuitry, are covered by a coverlay material and the covered inner core circuitry is exposed from the remaining layers of the PCB. The PCB having covered inner core circuitry is formed using a dummy core plus coverlay process. The select inner core circuitry is part of an inner core. The inner core corresponding to the covered inner core circuitry forms a flexible PCB portion. The flexible PCB portion is an extension of the remaining adjacent multiple layer PCB. The remaining portion of the multiple layer PCB is rigid. The inner core is common to both the flexible PCB portion and the remaining rigid PCB portion.

1 . A printed circuit board comprising:
 a. a rigid printed circuit board portion comprising a laminated stack of a plurality of non-conducting layers and a plurality of conductive layers, wherein the laminated stack further comprises a first portion of an inner core structure; and   b. a flexible printed circuit board portion comprising a second portion of the inner core structure, wherein the inner core structure is a continuous structure that extends through both the rigid printed circuit board portion and the flexible printed circuit board portion, further wherein the second portion of the inner core structure comprises inner core circuitry and exposed coverlay material covering the inner core circuitry, wherein the coverlay material comprises a continuous layer having a first portion in the flexible printed circuit board portion that is the exposed coverlay material covering the inner core circuitry and a second portion embedded within the laminated stack of the rigid printed circuit board portion, the second portion only partially extending into the rigid printed circuit board portion.   
     
     
         2 . The printed circuit board of  claim 1  wherein each of the conductive layers is pattern etched. 
     
     
         3 . The printed circuit board of  claim 1  further comprising one or more plated through hole vias in the rigid printed circuit board portion. 
     
     
         4 . The printed circuit board of  claim 1  wherein the rigid printed circuit board portion comprises a first rigid printed circuit board portion, further wherein the printed circuit board further comprises a second rigid printed circuit board portion comprising a second laminated stack of a plurality of non-conducting layers and a plurality of conductive layers, wherein the second laminated stack further comprises a third portion of the inner core structure, further wherein the flexible printed circuit board portion is coupled between the first rigid printed circuit board portion and the second rigid printed circuit board portion. 
     
     
         5 . The printed circuit board of  claim 1  wherein the inner core structure comprises an inner core non-conductive layer having a first surface and a first conductive layer positioned on the first surface of the inner core non-conductive layer. 
     
     
         6 . The printed circuit board of  claim 5  wherein the first conductive layer of the inner core structure comprises the inner core circuitry in the second portion of the inner core structure. 
     
     
         7 . The printed circuit board of  claim 6  wherein the inner core non-conductive layer has a second surface opposing the first surface, further wherein the inner core structure further comprises a second conductive layer positioned on the second surface of the inner core non-conductive layer. 
     
     
         8 . The printed circuit board of  claim 7  wherein the second conductive layer of the inner core structure comprises the inner core circuitry in the second portion of the inner core structure. 
     
     
         9 . The printed circuit board of  claim 5  wherein the inner core non-conductive layer comprises polyimide. 
     
     
         10 . The printed circuit board of  claim 1  wherein the coverlay material comprises a combination of polyimide and adhesive. 
     
     
         11 . A printed circuit board set form comprising:
 a. a plurality of printed circuit boards aligned within a common plane, wherein each printed circuit board is mechanically connected by a common substrate, further wherein each printed circuit board comprises:
 i. a rigid printed circuit board portion comprising a laminated stack of a plurality of non-conducting layers and a plurality of conductive layers, wherein the laminated stack further comprises a first portion of an inner core structure; and 
 ii. a flexible printed circuit board portion comprising a second portion of the inner core structure, wherein the inner core structure is a continuous structure that extends through both the rigid printed circuit board portion and the flexible printed circuit board portion, further wherein the second portion of the inner core structure comprises inner core circuitry and exposed coverlay material covering the inner core circuitry; and 
   b. a breakaway substrate aligned within the common plane and mechanically connected around a perimeter of the connected plurality of printed circuit boards, wherein the breakaway substrate includes a dummy core portion.   
     
     
         12 . The printed circuit board set form of  claim 9  wherein the breakaway substrate provides lateral structural stability to the connected plurality of printed circuit boards. 
     
     
         13 . The printed circuit board set form of  claim 9  wherein the plurality of printed circuit boards are electrically isolated from each other. 
     
     
         14 . A method of manufacturing a printed circuit board comprising:
 a. forming an inner core structure having an inner core circuitry on at least one surface of the inner core structure;   b. applying a coverlay material over the inner core circuitry;   c. forming a printed circuit board stack up, wherein the printed circuit board stack up comprises the inner core structure, a dummy core, one or more non-conductive layers and one or more conductive layers, wherein the dummy core is stacked on the coverlay material;   d. laminating the printed circuit board stack up, thereby forming a laminated stack;   e. forming a depth controlled rout from a surface of the laminated stack to the dummy core and around a perimeter of the dummy core, wherein a portion of the laminated stack within the perimeter of the rout and to a depth including the dummy core forms a laminated stack cap;   f. removing the laminated stack cap, thereby exposing the coverlay material and forming a flexible portion of the printed circuit board.   
     
     
         15 . The method of  claim 14  wherein the perimeter of the dummy core corresponds to a perimeter of the inner core circuitry. 
     
     
         16 . The method of  claim 14  further comprising forming the dummy core, wherein the dummy core comprises a non-conductive layer and a conductive layer. 
     
     
         17 . The method of  claim 16  wherein the dummy core is stacked on the coverlay material such that the conductive layer of the dummy core contacts the coverlay material. 
     
     
         18 . The method of  claim 14  further comprising forming at least one plated through hole via in the laminated stack prior to forming the depth controlled rout, wherein the at least one plated through hole via is not aligned within the inner core circuitry. 
     
     
         19 . The method of  claim 14  further comprising pattern etching the conductive layers in the laminated stack prior to forming the printed circuit board stack up. 
     
     
         20 . The method of  claim 14  wherein forming the inner core structure comprises applying a first conductive layer on a first surface of a non-conductive layer and applying a second conductive layer on a second surface of the non-conductive layer. 
     
     
         21 . The method of  claim 20  wherein the first conductive layer is pattern etched and the second conductive layer is pattern etched. 
     
     
         22 . The method of  claim 14  wherein the one or more non-conductive layers comprise one or more regular flow prepreg layers. 
     
     
         23 . The method of  claim 22  wherein laminating the printed circuit board stack up comprises applying a standard lamination pressure less than about 450 psi. 
     
     
         24 . The method of  claim 23  wherein a remaining portion of the laminated stack outside the perimeter of the rout forms a rigid portion of the printed circuit board, wherein an exposed outer surface of the laminated stack is smooth and non-rippled due to laminating the printed circuit board stack up using regular lamination pressure and the inclusion of regular flow prepreg. 
     
     
         25 . A printed circuit board comprising:
 a. a rigid printed circuit board portion comprising a laminated stack of a plurality of non-conducting layers and a plurality of conductive layers, wherein the plurality of non-conducting layers comprises a plurality of regular flow prepreg layers, further wherein an exposed outer surface of the laminated stack is smooth and non-rippled, wherein the laminated stack further comprises a first portion of an inner core structure; and   b. a flexible printed circuit board portion comprising a second portion of the inner core structure, wherein the inner core structure is a continuous structure that extends through both the rigid printed circuit board portion and the flexible printed circuit board portion, further wherein the second portion of the inner core structure comprises inner core circuitry, wherein an exposed lateral surface of the rigid printed circuit board forms a rigid-flexible boundary, wherein the rigid-flexible boundary formed at the exposed lateral surface is substantially smooth and regular.   
     
     
         26 . The printed circuit board of  claim 25  wherein the second portion of the inner core structure further comprises an exposed coverlay material covering the inner core circuitry. 
     
     
         27 . The printed circuit board of  claim 25  wherein the regular flow prepreg layers each comprise prepreg having resin flow greater than about 100 mil. 
     
     
         28 . (canceled) 
     
     
         29 . The printed circuit board of  claim 26  wherein the coverlay material comprises a continuous layer having a first portion in the flexible printed circuit board portion that is the exposed coverlay material covering the inner core circuitry and a second portion embedded within the laminated stack of the rigid printed circuit board portion, the second portion only partially extending into the rigid printed circuit board portion. 
     
     
         30 . The printed circuit board of  claim 1  wherein the first portion of the coverlay material in the flexible printed circuit board portion has a first surface facing the inner core circuitry and a second surface opposite the first surface, wherein an entirety of the second surface of the first portion of the coverlay material in the flexible printed circuit board portion is exposed.