Inverted CSP Stacking System and Method

Abstract

Two or more integrated circuits are stacked into a high density circuit module. The lower IC is inverted. Electrical connection to the integrated circuits is made by module contacts on a flexible circuit extending along the lower portion of the module. In one embodiment, the flexible circuit provides a balanced electrical connection to two CSP integrated circuits. In another embodiment, the flexible circuit provides a balanced electrical connection to inter-flex contacts of additional flexible circuits on two submodules. The additional flexible circuits provide further balanced connections to CSP integrated circuits in each submodule.

1 . A high density circuit module comprising: 
 two or more CSPs arranged one above the other to form a stack, the stack having a selected bottom CSP, each of the two or more CSPs having a first major surface and a second major surface and a plurality of CSP contacts arranged along the first major surface;    a form standard associated with the selected bottom CSP, the form standard comprising a portion disposed along the second major surface of the selected bottom CSP and flange portions that bend around sides of the selected bottom CSP;    at least one flexible circuit interconnecting the two or more CSPs, the at least one flexible circuit including a selected lower flexible circuit for connecting the module to an operating environment, a first portion of the selected lower flexible circuit being disposed along the selected lower portion of the form standard, the plurality of CSP contacts of the selected bottom CSP being in contact with a first side of the at least one flexible circuit, and the plurality of CSP contacts of a selected second CSP being in contact with a second side of the at least one flexible circuit; and    a plurality of module contacts attached to the first portion of the selected lower flexible circuit.    
   
   
       2 . The high density circuit module of  claim 1  in which a second form standard is associated with the selected second CSP in the stack of CSPs.  
   
   
       3 . The high density circuit module of  claim 1  in which the stack comprises two CSPs and one flexible circuit, and in which the flexible circuit includes one or more balanced conductive traces connecting to selected one or more first ones of the plurality of CSP contacts, respectively, on the selected bottom CSP, and connecting to a selected one or more second ones of the plurality of CSP contacts, respectively, on the selected second CSP.  
   
   
       4 . The high density circuit module of  claim 1  in which the stack comprises four CSPs and three flexible circuits, the three flexible circuits comprising a first submodule flexible circuit wrapped about a selected second CSP in the stack in a manner devised to connect the selected second CSP to the selected lower CSP, a second submodule flexible circuit wrapped about a selected third CSP in the stack in a manner devised to connect the selected third CSP to a selected fourth CSP in the stack, and a third flexible circuit being the selected lower flexible circuit wrapped about the selected lower CSP and the selected second CSP in a manner devised to connect the selected lower flexible circuit to the first submodule flexible circuit and the second submodule flexible circuit.  
   
   
       5 . The high density circuit module of  claim 4  in which the selected lower flexible circuit is connected to the selected first submodule flexible circuit and the second submodule flexible circuit with inter-flex contacts.  
   
   
       6 . The high density circuit module of  claim 5  in which the selected lower flexible circuit has a trace connecting to selected oppositely situated inter-flex contacts connecting to the first submodule flexible circuit and the second submodule flexible circuit.  
   
   
       7 . The high density circuit module of  claim 6  in which the first submodule flexible circuit has a trace connecting to selected oppositely situated CSP contacts on the selected lower CSP and the selected second CSP.  
   
   
       8 . The high density circuit module of  claim 6  in which the second submodule flexible circuit has a trace connecting to selected oppositely situated CSP contacts on the selected third CSP and the selected fourth CSP.  
   
   
       9 . A high density circuit module comprising: 
 two or more CSPs arranged one above the other to form a stack, the stack having a selected bottom CSP, each of the two or more CSPs having a first major surface and a second major surface and a plurality of CSP contacts arranged along the first major surface;    one or more flexible circuits interconnecting the two or more CSPs, the one or more flexible circuits having a selected lower flexible circuit for connecting the module to an operating environment, a first portion of the selected lower flexible circuit being disposed along the second major surface of the selected bottom CSP in the stack;    a plurality of module contacts attached to the first portion the selected lower flexible circuit;    the selected bottom CSP being in an inverted disposition such that its second major surface is disposed lower than its first major surface.    
   
   
       10 . The high density circuit module of  claim 9  in which the stack comprises two CSPs and one or more flexible circuits, and in which the one or more flexible circuits present one or more balanced conductive traces connecting to selected one or more first ones of the CSP contacts, respectively, on the first CSP and connecting to a selected one or more second ones of the CSP contacts, respectively, on the second CSP.  
   
   
       11 . The high density circuit module of  claim 9  in which the one or more flexible circuits each comprise two conductive layers.  
   
   
       12 . The high density circuit module of  claim 11  in which the one or more flexible circuits have opposing pairs of flex contacts connected by a via.  
   
   
       13 . A circuit module including: 
 a first CSP having first and second major surfaces and an array of contacts arranged along the first major surface;    a first form standard affixed to the second major surface of the first CSP;    a flexible circuit disposed about the form standard, the flexible circuit having a first side with a first set of flex contacts arranged along the first side, the first set of flex contacts connected to the array of contacts of the first CSP, the flexible circuit having a second side with a second set of flex contacts arranged along the second side, the second set of contacts being disposed opposite the first set of contacts, the flexible circuit having a third set of flex contacts and a fourth set of flex contacts;    a second CSP mounted to the second set of flex contacts, the second CSP in an inverted, stacked disposition relative to the first CSP.    
   
   
       14 . The circuit module of  claim 13  further comprising a first group of module contacts connected to the third set of flex contacts, and a second group of module contacts connected to the fourth set of flex contacts.  
   
   
       15 . The circuit module of  claim 13  in which the flexible circuit comprises at least a first conductive layer and a second conductive layer.  
   
   
       16 . The circuit module of  claim 13  in which the second set of flex contacts are accessible through windows in an outer layer of the flexible circuit.  
   
   
       17 . A circuit module comprising: 
 a first CSP and a second CSP, the first CSP being disposed in an inverted, stacked relationship with respect to the second CSP, each of the CSPs having a first major side and a second major side with a set of CSP contacts disposed on the first major side, the first major side of the first CSP being disposed to face toward the first major side of the second CSP;    a flexible circuit interconnecting the first and second CSPs, the flexible circuit being wrapped about the first CSP to present a first portion aligned with and disposed beneath the second major side of the first CSP;    module contacts disposed along the first portion of the flexible circuit.    
   
   
       18 . The circuit module of  claim 17  in which the flexible circuit has conductive traces connecting selected ones of the module contacts to selected associated ones of the CSP contacts on the first CSP and to selected associated ones of CSP contacts on the second CSP, the conductive traces each presenting a conductive path with a substantially equal electrical delay to their respective connected CSP contacts.  
   
   
       19 . A high density memory module comprising: 
 a first CSP and a second CSP each having first and second major sides and a plurality of CSP contacts arranged along the first major side, wherein one of the first CSP and the second CSP is a selected bottom CSP, which is in an inverted disposition such that its second major side is disposed lower than its first major side;    a flexible circuit for connecting the first and second CSPs to an operating environment, the flexible circuit having a plurality of module contacts, a selected one or more of the module contacts being connected with a conductive trace to a selected one or more opposing pairs of flex contacts, each of the opposing pairs of flex contacts having connected to it at least one of the plurality of CSP contacts of the first CSP and at least one of the plurality of CSP contacts of the second CSP.    
   
   
       20 . A circuit module comprising: 
 two or more CSPs arranged in a stack one above the other, each of the two or more CSPs having a first major surface and a second major surface and a plurality of CSP contacts arranged along the first major surface, the stack having a selected bottom CSP, the selected bottom CSP being in an inverted disposition such that its second major surface is below its first major surface;    one or more flexible circuit interconnecting the two or more CSPs.    
   
   
       21 . The circuit module of  claim 20  in which at least one of the one or more flexible, circuits presenting a first portion below the selected bottom CSP, the first portion having module contacts for connecting the circuit module to an operating environment.  
   
   
       22 . The circuit module of  claim 20  further comprising one or more form standards disposed about selected ones of the two or more CSPs.  
   
   
       23 . The circuit module of  claim 21  in which the flexible circuit comprises one or more opposing pairs of interconnected flex contacts connected to one or more conductive traces, respectively, the one or more conductive traces connected to respective ones of the module contacts.  
   
   
       24 . A high density circuit module comprising: 
 two or more CSPs in a stacked disposition one above the other, each of the two or more CSPs having an array of CSP contacts arranged along a major surface, wherein one of the two or more CSPs is a selected bottom CSP, which is in an inverted disposition such that its major surface faces the major surface of the other of the two or more CSPs;    means for making balanced electrical connections from an operating environment to selected corresponding CSP contacts on a selected two or more of the two or more CSPs.    
   
   
       25 . The high density circuit module of  claim 24  further including submodule interconnection means for making balanced electrical connections to selected corresponding CSP contacts on selected adjacent pairs of the two or more CSPs.  
   
   
       26 . The high density circuit module of  claim 24  further including: 
 two or more submodule interconnection means for making balanced electrical connections to selected corresponding CSP contacts on selected adjacent pairs of the two or more CSPs,    module interconnection means for making balanced electrical connections to selected corresponding submodule contacts on selected adjacent pairs of the two or more submodule interconnection means.    
   
   
       27 . A method of forming a balanced connection to two CSPs in a high density memory module, the method comprising the steps: 
 providing a flexible circuit having an opposing pair of interconnected flex contacts;    attaching a first CSP contact of a first CSP to one of the interconnected flex contacts;    attaching a second CSP contact of a second CSP to an opposing flex contact associated with the flex contact to which the first CSP contact is soldered;    attaching a module contact to a flex contact associated with a conductive trace connected to the opposing pair of interconnected flex contacts.    
   
   
       28 . The method of  claim 27  further comprising the step of wrapping the flexible circuit around the first CSP.  
   
   
       29 . The method of  claim 28  further comprising the step of attaching the flexible circuit to the body of the first CSP.  
   
   
       30 . The method of  claim 27  further comprising the step of wrapping the flexible circuit around a form standard associated with the first CSP.  
   
   
       31 . The method of  claim 30  further comprising the step of attaching the flexible circuit to the form standard.  
   
   
       32 . A method of making a high density circuit module comprising the steps: 
 providing a flexible circuit having a first flex contact pad array on a first major side, a second flex contact pad array, oppositely disposed from the first flex contact pad array, on a second major side, and a third flex contact pad array on the first major side;    connecting a first CSP to the first flex contact pad array;    wrapping the flexible circuit about the first CSP;    connecting a second CSP to the second flex contact pad array;    attaching module contacts to the third flex contact pad array.    
   
   
       33 . The method of  claim 32  further including the step of inverting the first CSP after the step of wrapping the flexible circuit and before the step of connecting the second CSP.  
   
   
       34 . The method of  claim 32  further including the step of attaching module contacts to a fourth flex contact pad array on the first major side of the flexible circuit.  
   
   
       35 . The method of  claim 32  further including the step of attaching a form standard to the first CSP before wrapping the flexible circuit about the first CSP.  
   
   
       36 . The method of  claim 35  further including the step of attaching the flexible circuit to the form standard.