Stacked modules and method

Abstract

The present invention stacks integrated circuits into modules that conserve board surface area. In a precursor assembly devised as a component for a stacked circuit module in accordance with a preferred embodiment of the present invention, one or more stiffeners are disposed at least partially between a flex circuit and an integrated circuit. In a two-high stacked circuit module devised in accordance with a preferred embodiment of the present invention, an integrated circuit is stacked above a precursor assembly. The two integrated circuits are connected with the flex circuit of the precursor assembly. The present invention may be employed to advantage in numerous configurations and combinations of integrated circuits in modules.

1 . An assembly devised as a component for a stacked circuit module comprising: 
 a first CSP comprising 
 a package body having upper and lower major surfaces and first and second lateral sides,  
 a lateral extent defined by the first and second lateral sides,  
 first CSP contacts disposed along the lower major surface, and  
 a mounting height defined by the first CSP contacts;  
   a flex circuit configured for external electrical connection of the first CSP, the flex circuit comprising 
 lower flex contacts connected to selected ones of the first CSP contacts, and  
 first and second upper portions terminated by first and second edges, respectively, the first and second upper portions of the flex circuit being disposed above the upper major surface of the first CSP, and the first and second edges being disposed a preselected distance apart within the lateral extent defined by the first and second lateral sides; and  
   first and second generally planar stiffeners each attached to the lower major surface of the first CSP and each having a thickness that does not exceed the mounting height, the first generally planar stiffener being disposed along the first lateral side of the first CSP and the second generally planar stiffener being disposed along the second lateral side of the first CSP.    
   
   
       2 . The assembly of  claim 1  in which the flex circuit has plural conductive layers.  
   
   
       3 . The assembly of  claim 1  in which the first and second generally planar stiffeners are disposed within the lateral extent defined by the first and second lateral sides.  
   
   
       4 . The assembly of  claim 1  in which portions of the first and second generally planar stiffeners are disposed outside the lateral extent defined by the first and second lateral sides.  
   
   
       5 . The assembly of  claim 1  in which the first and second generally planar stiffeners are attached to the flex circuit with adhesive.  
   
   
       6 . The assembly of  claim 5  in which the adhesive is a dry film adhesive.  
   
   
       7 . The assembly of  claim 1  in which the first and second generally planar stiffeners are attached to the first CSP with adhesive.  
   
   
       8 . The assembly of  claim 7  in which the adhesive is a liquid adhesive.  
   
   
       9 . The assembly of  claim 1  in which the first CSP contacts at least partially project into a volume between the first and second generally planar stiffeners.  
   
   
       10 . The assembly of  claim 1  in which the first upper portion exhibits first upper flex contacts and the second upper portion exhibits second upper flex contacts, the first and second upper flex contacts being collectively configured for connection to a second CSP.  
   
   
       11 . The assembly of  claim 1  in which the first and second generally planar stiffeners comprise one or more laminated layers of polyimide film having mechanical properties compatible with the mechanical properties of the flexible circuit.  
   
   
       12 . The assembly of  claim 9  in which the first and second generally planar stiffeners comprise one or more laminated layers of polyimide film having mechanical properties compatible with the mechanical properties of the flexible circuit.  
   
   
       13 . The assembly of  claim 3  or  4  in which: 
 the first and second generally planar stiffeners are attached to the flex circuit with adhesive;    the first and second generally planar stiffeners are attached to the first CSP with adhesive;    the first CSP contacts at least partially project into a volume between the first and second generally planar stiffeners;    the first upper portion exhibits first upper flex contacts and the second upper portion exhibits second upper flex contacts, the first and second upper flex contacts being collectively configured for connection to a second CSP; and    the first and second generally planar stiffeners comprise one or more laminated layers of polyimide film having mechanical properties compatible with the mechanical properties of the flexible circuit.    
   
   
       14 . A stacked circuit module comprising: 
 an assembly devised according to  claim 1;  and    a second CSP disposed above the assembly and connected to the flex circuit.    
   
   
       15 . A stacked circuit module comprising: 
 an assembly devised according to  claim 13;  and    a second CSP connected to the flex circuit.    
   
   
       16 . An assembly devised as a component for a stacked circuit module comprising: 
 a first CSP having upper and lower major surfaces, first and second lateral sides, and first CSP contacts disposed along the lower major surface;    a flex circuit configured for external electrical connection of the first CSP, the flex circuit comprising 
 lower flex contacts connected to selected ones of the first CSP contacts, and  
 first and second upper portions terminated by first and second edges, respectively, the first upper portion of the flex circuit being disposed above the upper major surface of the first CSP along the first lateral side, the second upper portion of the flex circuit being disposed above the upper major surface of the first CSP along the second lateral side, and the first and second edges being disposed a preselected distance apart above the first CSP;  
   a stiffener attached to the lower major surface of the first CSP.    
   
   
       17 . The assembly of  claim 16  in which the first CSP contacts at least partially project below the lower major surface of the first CSP.  
   
   
       18 . The assembly of  claim 16  in which the stiffener disposes the lower flex contacts apart from the lower major surface of the first CSP.  
   
   
       19 . The assembly of  claim 18  in which the flex circuit has plural conductive layers.  
   
   
       20 . A high-density circuit module comprising: 
 a stack comprising 
 first and second lateral sides,  
 a first CSP having a first major surface along which a first plurality of CSP contacts is disposed and a second major surface, and  
 a second CSP having a major surface along which a second plurality of CSP contacts is disposed;  
   a flex circuit having at least one outer layer, a first generally planar portion disposed adjacent to at least a portion of the first major surface of the first CSP, a second generally planar portion disposed adjacent to at least a portion of the second major surface of the first CSP, and a folded portion disposed adjacent to first lateral side of the stack;    sets of flex contacts, respectively comprising a first plurality of flex contacts along a first side of the first generally planar portion of the flex circuit, a second plurality of flex contacts along the second generally planar portion of the flex circuit, and a third plurality of flex contacts disposed along a second side of the first generally planar portion of the flex circuit;    a plurality of module contacts;    conductive connections between ones of the first plurality of CSP contacts and ones of the first plurality of flex contacts;    conductive connections between ones of the second plurality of CSP contacts and ones of the second plurality of flex contacts; and    conductive connections between ones of the plurality of module contacts and ones of the third plurality of flex contacts.    
   
   
       21 . The high-density circuit module of  claim 20  in which the flex circuit comprises a plurality of conductive layers, and a first of the conductive levels comprises a ground plane.  
   
   
       22 . The high-density circuit module of  claim 21  in which a second of the conductive levels has plural electrical paths, each between a selected one of the contacts of the first plurality of CSP contacts and a selected one of the contacts of the second plurality of CSP contacts.  
   
   
       23 . The high-density circuit module of  claim 22  in which the second conductive layer comprises a voltage plane, and the electrical paths comprise traces.  
   
   
       24 . The high-density circuit module of  claim 22  in which selected ones of the electrical paths have substantially equal signal lengths.  
   
   
       25 . The high-density circuit module of  claim 24  in which the second conductive layer comprises a voltage plane, and the electrical paths comprise traces.  
   
   
       26 . The high-density circuit module of  claim 20  in which the flex circuit further comprises a third generally planar portion disposed adjacent to at least a portion of the second major surface of the first CSP, and a folded portion disposed adjacent to second lateral side of the stack.  
   
   
       27 . The high-density circuit module of  claim 20  or  25  in which the flex circuit is attached to a stiffener disposed along the first major surface of the first CSP.  
   
   
       28 . The high-density circuit module of  claim 20  in which the flex circuit is attached to a stiffener disposed along the first major surface of the first CSP, the stiffener disposing the first plurality of flex contacts apart from the first major surface of the first CSP but in contact with the first plurality of CSP contacts.  
   
   
       29 . An assembly devised as a component for a stacked circuit module comprising: 
 a first CSP comprising upper and lower major surfaces and first CSP contacts disposed along the lower major surface;    a flex circuit comprising plural conductive layers, lower flex contacts, and a first upper portion disposed above the upper major surface of the first CSP; and    a stiffener attached to the lower major surface of the first CSP and to the flex circuit.    
   
   
       30 . The assembly of  claim 29  in which the stiffener is configured to dispose the lower flex contacts of the flex circuit below the lower major surface of the first CSP.  
   
   
       31 . The assembly of  claim 30  in which the first CSP contacts emerge from the lower major surface of the first CSP and contact the lower flex contacts below the lower major surface of the first CSP.  
   
   
       32 . The assembly of  claim 29  in which the stiffener is disposed within a lateral extent defined by first and second lateral sides of the first CSP.  
   
   
       33 . The assembly of  claim 29  in which a portion of the stiffener is disposed outside a lateral extent defined by first and second lateral sides of the first CSP.  
   
   
       34 . The assembly of  claim 29  in which the stiffener is attached to the flex circuit with adhesive.  
   
   
       35 . The assembly of  claim 34  in which the adhesive is a dry film adhesive.  
   
   
       36 . The assembly of  claim 29  in which the stiffener is attached to the first CSP with adhesive.  
   
   
       37 . The assembly of  claim 36  in which the adhesive is a liquid adhesive.  
   
   
       38 . The assembly of  claim 29  in which the first upper portion of the flex circuit exhibits upper flex contacts configured for connection to a second CSP.  
   
   
       39 . The assembly of  claim 29  further comprising first upper flex contacts along the first upper portion of the flex circuit and second upper flex contacts along a second upper portion of the flex circuit, the first upper flex contacts and second upper flex contracts collectively configured for connection to a second CSP.  
   
   
       40 . The assembly of  claim 29  in which the stiffener comprises one or more laminated layers of polyimide film having mechanical properties compatible with the mechanical properties of the flexible circuit.  
   
   
       41 . The assembly of  claim 29  in which the flex circuit comprises a first fiducial defined by a generally square metallic region and a second fiducial defined by a cross-shaped metallic region, the first and second fiducials being asymmetrically disposed along the flex circuit.  
   
   
       42 . The assembly of  claim 40  in which 
 the stiffener is about 0.13 mm thick    the stiffener is attached to the flex circuit with a dry film adhesive about 0.05 mm thick;    the stiffeners is attached to the first CSP with liquid adhesive between about 0.04 mm. to 0.10 mm thick; and    the first upper portion of the flex circuit is attached to the upper major surface of the first CSP with a dry film adhesive about 0.08 mm thick.    
   
   
       43 . A method for constructing an assembly devised for employment in a stacked circuit module, the method comprising the steps of: 
 providing a first CSP comprising upper and lower major surfaces and first CSP contacts disposed along the lower major surface;    providing a flex circuit comprising lower flex contacts, and first and second upper portions terminated by first and second edges, respectively;    providing a stiffener;    attaching the stiffener to the flex circuitry;    attaching the stiffener to the lower major surface of the first CSP;    disposing the first and second upper portions of the flex circuitry above the upper major surface of the first CSP; and    imposing a preselected distance between the first and second edges.    
   
   
       44 . The method of  claim 43  in which a physical form is used to impose a preselected distance between the first and second edges.  
   
   
       45 . The method of  claim 44  in which a portion of the physical form is placed between the first and second edges.  
   
   
       46 . The method of  claim 43  in which the flex circuit comprises a fiducial, the method further comprising the steps of referring the fiducial and disposing the first CSP along the flex circuit.  
   
   
       47 . The method of  claim 43  in which the stiffener is provided in a first aggregation having other stiffeners and the flex circuit is provided in a second aggregation having other flex circuits, the method further comprising the steps of referring to a fiducial comprised in the second aggregation and singulating the assembly from the first and second aggregations.  
   
   
       48 . The method of  claim 47  in which the second aggregation comprises a trim tab having conductive bussing, the flex circuit of the assembly has an end portion having no conductive bussing, and the step of singulating comprises the steps of separating the trim tab from the flex circuit of the assembly and separating end portion of the flex circuit of the assembly from the second aggregation.  
   
   
       49 . A method for constructing a stacked circuit module, the method comprising the steps of: 
 constructing an assembly devised for employment in a stacked circuit module in accordance with  claim 43;     providing a second CSP; and    disposing the second CSP above the assembly and connecting the second CSP to the flex circuit.    
   
   
       50 . A tooling apparatus for constructing an assembly devised for employment in a stacked circuit module, the tooling apparatus comprising: 
 a jig;    a cavity configured to receive a CSP and a flex circuit; and    a forming tool configured to dispose upper portions of a flex circuit received in the cavity along an upper surface of a CSP received in the cavity.    
   
   
       51 . The tooling apparatus of  claim 50  further comprising a physical form configured to impose a preselected distance between a first edge and a second edge of a flex circuit received in the cavity.  
   
   
       52 . The tooling apparatus of  claim 51  further comprising a press tool configured to impose portions of a flex circuit received in the cavity on an upper surface of a CSP received in the cavity.  
   
   
       53 . The tooling apparatus of  claim 52  in which the press tool is heated.  
   
   
       54 . A method for constructing an assembly devised for employment in a stacked circuit module, the method comprising the steps of: 
 providing a tooling apparatus in accordance with  claim 50;     disposing a CSP, a stiffener, and a flex circuit in the cavity of the tooling apparatus to deflect a first upper portion and a second upper portion of the flex circuit upward; and    disposing the first and second upper portions of the flex circuit along an upper surface of the CSP with the forming tool.    
   
   
       55 . The method for constructing an assembly of  claim 54  in which the tooling apparatus further comprises a physical form, the method further comprising the step of using the physical form to impose a preselected distance between a first edge and a second edge of the flex circuit.  
   
   
       56 . The method for constructing an assembly of  claim 55  in which the tooling apparatus further comprises a press tool, the method further comprising the step of using the press tool to impose the first and second upper portions of the flex circuit on an upper surface of the CSP.  
   
   
       57 . The method for constructing an assembly of  claim 56 , the method further comprising the step of heating the press tool.  
   
   
       58 . A tooling apparatus for constructing an assembly devised for employment in a stacked circuit module, the tooling apparatus comprising: 
 an adjustable jig;    a preform tool; and    a cavity configured to receive a CSP and a flex circuit, the cavity being defined at least in part by the adjustable jig.    
   
   
       59 . The tooling apparatus of  claim 58  further comprising a physical form configured to impose a preselected distance between a first edge and a second edge of a flex circuit received in the cavity.  
   
   
       60 . The tooling apparatus of  claim 59  further comprising a press tool configured to impose portions of a flex circuit received in the cavity on an upper surface of a CSP received in the cavity.  
   
   
       61 . The tooling apparatus of  claim 60  in which the press tool is heated.  
   
   
       62 . The tooling apparatus of  claim 61  further comprising a forming tool.  
   
   
       63 . A method for constructing an assembly devised for employment in a stacked circuit module, the method comprising the steps of: 
 providing a tooling apparatus in accordance with  claim 58;     adjusting the jig to a first configuration;    disposing a CSP, a stiffener, and a flex circuit in the cavity of the tooling apparatus    using the preform tool to deflect a first upper portion and a second upper portion of the flex circuit upward to a first flex configuration;    adjusting the jig to a second configuration; and    disposing the CSP, the stiffener, and the flex circuit in the cavity of the tooling apparatus to deflect the first upper portion and the second upper portion of the flex circuit upward to a second flex configuration.    
   
   
       64 . The method for constructing an assembly of  claim 63  in which the tooling apparatus further comprises a physical form, the method further comprising the step of using the physical form to impose a preselected distance between a first edge and a second edge of the flex circuit.  
   
   
       65 . The method for constructing an assembly of  claim 64  in which the tooling apparatus further comprises a press tool, the method further comprising the step of using the press tool to impose the first and second upper portions of the flex circuit on an upper surface of the CSP.  
   
   
       66 . The method for constructing an assembly of  claim 65 , the method further comprising the step of heating the press tool.  
   
   
       67 . The method for constructing an assembly of  claim 65  in which the tooling apparatus further comprises a forming tool, the method further comprising the step of disposing the first and second upper portions of the flex circuit along an upper surface of the CSP with the forming tool.