Abstract:
In one embodiment a method is provided. A method comprising forming a plurality of electromechanical formations to electromechanical couple a first printed circuit board to a second printed circuit board, wherein each electromechanical formation is of a first size; and forming at least one anchoring formation to anchor the first printed circuit board to the second printed circuit board, each anchoring formation being formed at a selected anchor point, and being of a second size which is greater than the first size.

Description:
FIELD OF THE INVENTION  
       [0001]     Embodiments of the invention relate to surface mount technology (SMT) in which a first printed circuit board is electromechanically coupled to a second printed circuit board.  
       BACKGROUND  
       [0002]     In surface mount technology (SMT) a first printed circuit board (PCB) may be electromechanically coupled to a second printed circuit board (PCB) through electromechanical formations in the form of solder joints formed between an underside of the first PCB, and an upper side of the second PCB. The first PCB may be a substrate board which is likewise electromechanically coupled to a semiconductor die comprising an integrated circuit. The second PCB may be a motherboard for mounting the substrate board and semiconductor die combination. The semiconductor die and substrate board combination is usually referred to as a semiconductor package.  
         [0003]     Each electromechanical formation forms an input/output (I/O) to the integrated circuit. As I/O counts increase, more electromechanical formations are required, and thus a size of each electromechanical formation has to be decreased in order to accommodate the electromechanical formations within the same area. Decreasing the size of the electromechanical formations makes them more fragile with the result that stress in the for of deformation along the peripheral edges of the first PCB due to coefficient of thermal expansion (CTE) mismatches between the first and second PCBs, leads to failure of the electromechanical formations formed along the peripheral edges.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  illustrates a flip-chip assembly process, in accordance with prior art;  
         [0005]      FIG. 2  shows a carrier board with a plated area in accordance with one embodiment of the invention;  
         [0006]      FIG. 3  shows an anchoring formation/joint formed between a carrier board and a substrate board, in accordance with one embodiment of the invention;  
         [0007]      FIG. 4  illustrates a stencil used to print solder material over the plated areas of a carrier board, in accordance with one embodiment of the invention;  
         [0008]      FIG. 5  shows the shapes of different plated areas of a carrier board, in accordance with one embodiment of the invention;  
         [0009]      FIG. 6  illustrates a wraparound solder joint formed between a carrier board and a substrate board, in accordance with one embodiment of the invention;  
         [0010]      FIG. 7  illustrates a modified solder printing technique, in accordance with one embodiment of the invention;  
         [0011]      FIGS. 8 and 9  illustrate different embodiments of anchoring formations formed between a carrier board and a substrate board, in accordance with one embodiments of the invention;  
         [0012]      FIG. 10  illustrates a de-paneling technique, in accordance with one embodiment of the invention; and  
         [0013]      FIG. 11  shows the components of a system, in accordance with one embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0014]     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to avoid obscuring the invention.  
         [0015]     Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments.  
         [0016]      FIG. 1A  of the drawings illustrates the flip-chip assembly process of the prior art. Referring to  FIG. 1A , processing component  10  includes a first printed circuit board in the form of substrate board  12  which is mounted to a second printed circuit board in the form of a carrier or motherboard  26 . The substrate board  12  has a semiconductor die  16  mounted on an operatively upper side  14  thereof, whereas an operatively under side  18  of the substrate board  12  includes solder bumps  20  (as can be seen in  FIG. 1B  of the drawings) formed thereon. During the flip-chip assembly process, the solder bumps  20  are aligned with corresponding solder bumps  22  formed on an operatively upper side  24  of a second printed circuit board in the form of a carrier or motherboard  26 . The components  12  and  26  are brought into contact and a reflow operation is performed to reflow the solder bumps  22  and  20  so that an electromechanical solder joint  27  is formed between the components (see  FIG. 1C  of the drawings).  
         [0017]     In one embodiment of the present invention, the above-described flip-chip assembly process includes the formation of at least one of anchoring formation in addition to the solder joints  27 . The purpose of the anchoring formation is to anchor the substrate  12  to the motherboard  26  thereby to at least reduce failure of the solder joints  27  due to relative movement between substrate  12  and the motherboard  26 , for example, due to coefficient thermal of execution (CTE) mismatches between these components.  
         [0018]     Accordingly, in one embodiment of the invention, a motherboard such as the motherboard  30  shown in  FIG. 2  of the drawings is used. As before, the motherboard  30  includes a plurality of solder bumps  22 . However, in addition to the solder bumps  22 , the motherboard  30  also includes plated areas  32 . The plated areas  32  are comprised of a solder-wettable material and are located at selected anchor points on the motherboard  30 . In the example shown in  FIG. 2  of the drawings, the anchor points are located at the four corners of the motherboard  30 .  
         [0019]     In accordance with the techniques disclosed herein, to be compatible with the motherboard  30 , the substrate board  12  is modified so that the under side  18  thereof includes complementary plated areas (not shown) that match the complementary plated area  32  of the motherboard  30 . For example, referring the  FIG. 3  of the drawings, the substrate board  12  is shown to include a complementary plated area  34  formed on the under side  18 . The plated area  34  is complementary to and matches the complementary plated area  32  of the motherboard  30 . During the flip-chip assembly process, the complementary plated area  32  of the motherboard  30  is coated with a solder material. For example, a solder printing stencil  36  (see  FIG. 4  of the drawings) may be placed over the motherboard  30  in order to deposit the solder material over the complementary plated area  32 . As will the seen, the stencil  36  includes openings  38  which match the complementary plated area  32 . Referring again to  FIG. 3A  of the drawings, during the flip-chip assembly process, the substrate board  12  is brought into contact with the motherboard  30  so that the deposited solder material (not shown) is sandwiched between the plated areas  34 ,  32  of the motherboard  30  and the substrate board  12 , respectively. Thereafter, a solder reflow operation is performed in order to form an anchoring formation/joint  40  between each complementary plated area  34  of the substrate  12  and its corresponding plated area  32  of the motherboard  30 . The anchoring formation/joint  40  is larger than the solder joint  27 .  
         [0020]     Various shapes and configurations are possible for the complementary plated areas  32  and  34 . Referring to  FIG. 5  of the drawings, a few of such configurations and shapes are illustrated. For example, the plated areas may be square (see  FIG. 5A ), the plated areas may have an arcuate shape (see  FIG. 5B  of the drawings), the plated areas may include a number of rectangular sub-areas (see  FIG. 5C ), or the plated areas may include a single rectangular area (see  FIG. 5D ) of the drawings.  
         [0021]     It will be appreciated, that the resultant anchoring formations/joints illustrated thus far have been restricted to a single plane. However, it is possible, in some embodiments, to form an anchoring formation/joint that is not limited to a single plane. One example of an anchoring formation/joint that is formed to anchor the substrate  12  to the motherboard  30 , that is not limited to being in a single plane is illustrated in  FIGS. 6A and 6B  of the drawings. Referring the  FIG. 6A , a motherboard  14  includes a rectangular-shaped plated area  32 , and a substrate board  12  includes an L-shaped complementary plated area  34 . The L-shaped complementary area  34  extends along the under side  18  of the substrate  12  and along an edge  19  that is transverse to the under side  18 . In order to form the anchoring formation/joint between the plated areas, solder material is deposited over the plated area  32  and the components  12 ,  30  are brought into contact, whereafter a solder reflow operation is performed. The resultant anchor joint  42  is shown in  FIG. 6B  of the drawings, and referred to as a wraparound solder joint since the joint itself wraps around the under side  18  and the edge  19  of the substrate board  12 . To form the wraparound solder joint  42 , a sufficient amount of solder material has to be deposited on the plated area  32 . Accordingly, the stencil  36  that is used to print the solder material onto the plated area  32  has apertures  38  that are larger than the dimensions of the actual plated area  32 , as can be seen in  FIG. 7  of the drawings.  
         [0022]     In order to improve the strength of the resultant in anchoring formation/joint, in some embodiments, the solder material may actually extend into the substrate  12 . For example in the embodiment shown in  FIG. 8  of the drawings, circular, or disc-shaped plated areas are formed on a substrate  30 , and a motherboard  30 , respectively. Next, plated thru-holes (vias)  44 ,  46  are formed, for example by drilling, into the substrate  12 , and the motherboard  30 , respectively. The presence of the plated thru-holes  44 ,  46 , allow the solder material that is deposited during the flip-chip assembly process to move partially into the plated thru-holes  44 ,  46  so that the resultant anchoring formation/joint  48  formed after the solder reflow operation extends partly into the substrate board  12  and the motherboard  30 , as can be seen in  FIG. 8B  of the drawings.  
         [0023]     In one embodiment, a wraparound solder joint may be formed, as is shown in  FIG. 9A  of the drawings, with a difference that part of the material of the wraparound solder joint that is adjacent to the side edge  19  of the substrate board  12 , actually extends into the substrate board  12  itself. For this embodiment, the substrate board  12  includes a plated area  34  along its side edge  19  with the characteristic that the plated area  34  extends, at least partly into the substrate board  12 . For example, referring the  FIG. 9  of the drawings, the plated area  34  includes two end sections  34 . 1  that are flush with the side edge  19  of the substrate board  12 , and a middle section  34 . 2  which is channel-shaped and extends into the side  19  of the substrate board  12 . The resultant wraparound solder joint for this configuration of the plated areas  34 ,  32  is shown in  FIG. 9B  of the drawings, and as will be seen includes solder material that extends into the substrate board  12 .  
         [0024]     In order to form the plated area  34 . 2  shown in  FIG. 9A  of the drawings, a de-panel process used to separate or de-panel the substrate board  12  from other substrate boards  12  is modified as follows. Referring to  FIG. 10 , a component panel  50  is fabricated in conventional fashion, to include a plurality of components substrates  52 . Scribe lines  54  are formed between the component substrates  52  in order to facilitate separation of the component substrates  52  from the component panel  50 . Before the actual separation, in one embodiment of the invention, vias  54  are drilled into the component panel  50  to coincide with the scribe lines  56 . For example, in one embodiment, the vias  54  are circular in shape and each vias  54  straddles a single scribe line  56  so that when the components are separated, each half of a via  50  that straddled a scribe line  56  forms a channel-shape. Before separation, the vias  54  are plated with a solder-wettable material using a conventional plated process.  
         [0025]      FIG. 11  shows a system  60  in accordance with one embodiment of the present invention, the system includes a processing component  62  which is coupled to a memory  64 , via communications interface, such as a bus  66 . The processing component includes a substrate package which includes a substrate board  12  and semiconductor die  16 , and a carrier board  30  which is coupled to the substrate package, as described above.  
         [0026]     Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that the various modification and changes can be made to these embodiments without departing from the broader spirit of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than in a restrictive sense.