Abstract:
An electronic apparatus and method of fabrication of the apparatus, the apparatus including a first electronic device having an interconnection surface with a first plurality of interconnection pads extending from the surface by a first distance and a second plurality of alignment posts extending from the surface by a second distance greater than the first distance, and a second electrical device having an interconnection surface with a first plurality of electrical interconnection pads, each pad arranged to contact a corresponding first electronic device interconnection surface pad upon assembly of the first electronic device interconnection surface upon the second electronic device interconnection surface, the second electronic device interconnection surface including a third plurality of alignment posts, each located to be adjacent to at least one of the first electronic device alignment posts upon assembly.

Description:
RELATED APPLICATION 
       [0001]    This application is related to the following co-pending U.S. patent application having the same assignee: “OVERCOMING LAMINATE WARPAGE AND MISALIGNMENT IN FLIP-CHIP PACKAGES,” (U.S. patent application Ser. No. 11/671,485 filed Dec. 18, 2009). 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to integrated circuitry manufacturing. In particular, the present invention relates to semiconductor packaging. 
         [0004]    2. Description of the Related Art 
         [0005]    Integrated circuit products include a manufactured semiconductor device or ‘chip’ mounted onto a package in order to provide electronic signal, power and ground interconnections to other devices for electronic product manufacture. This requires that the semiconductor chip be physically and electrically interconnected the packaging containing a substrate. The chip includes pads that each provide for a signal or power/ground interconnection to corresponding pads located on the substrate. Typically a solder alloy is provided on the semiconductor chip pads and on the substrate pads that are to be interconnected. Interconnection is provided during an assembly process by placing the chip pads onto the substrate pads using a high temperature to melt and reflow the solder from the semiconductor chip and the substrate to join the chip to the substrate and electrically interconnect the pads. 
         [0006]    In some assembly processes the substrate pads include solid solder which is fabricated by applying presolder which is reflowed as part of the laminate fabrication process. When presolder is used, the reflowed solder forms domes or hemispheres due to the surface tension of the molten solder during the reflow process.  FIG. 1  illustrates a chip  100  including solder bumps or domes such as  102  and  104  and a substrate  110  including solder bumps or domes  106  and  108 .  FIG. 2  illustrates a chip  200  including pillars  202  and  206  with solder bumps  204  and  208 . In  FIG. 2 , the substrate  214  includes solder bumps or domes  210  and  212  similar to the substrate  110  in  FIG. 1 .  FIG. 2  illustrates that placing the chip  200  onto the substrate  214  can result in misalignment caused by the bump or dome shapes on both the chip and semiconductor sliding laterally when during assembly resulting in a lateral shift of the chip relative to the substrate. 
         [0007]    One prior art solution has been to flatten the bumps or domes on the substrate. This process is referred to as bump flattening or coining. However, coining adds an extra process step and requires specialized equipment. Also, coining can be a contributor to yield loss during laminate fabrication. Therefore the addition of the coining process step is expensive and can result in lower yield. 
         [0008]    Further, as technology progresses, semiconductor chips have become more complex and chip size has decreased. This results in a greater number of smaller interconnection pads on a smaller chip surface. Therefore, alignment of the chip interconnection pads with the corresponding interconnection pads of the substrate becomes a greater challenge. 
       SUMMARY 
       [0009]    In accordance with the present invention, an electronic apparatus is provided that includes a first electronic device having an interconnection surface with a first plurality of interconnection pads extending from the surface by a first distance and a second plurality of alignment posts extending from the surface by a second distance greater than the first distance, and a second electrical device having an interconnection surface with a first plurality of electrical interconnection pads, each pad being arranged to contact a corresponding first electronic device interconnection surface pad upon assembly of the first electronic device interconnection surface upon the second electronic device interconnection surface, the second electronic device interconnection surface including a third plurality of alignment posts, each located to be adjacent to at least one of the first electronic device alignment posts upon assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. 
           [0011]      FIG. 1  is a side view illustration of a prior art assembly of a chip upon a substrate; 
           [0012]      FIG. 2  is a side view illustration of a prior art assembly of a chip including pillars upon a substrate; 
           [0013]      FIG. 3  is a side view illustration of a chip including alignment posts and a substrate with alignment bumps; 
           [0014]      FIG. 4  is a side view illustration of a second embodiment of a chip including alignment posts and a substrate with alignment bumps; 
           [0015]      FIG. 5  is a top view illustration of the chip including alignment posts and a substrate with alignment bumps of  FIG. 3 ; 
           [0016]      FIG. 6  is a top view illustration of the second embodiment of the chip including alignment posts and a substrate with alignment bumps of  FIG. 4 ; 
           [0017]      FIG. 7  is a top view illustration of a third embodiment of a chip including alignment posts and a substrate with alignment bumps; and 
           [0018]      FIG. 8  is a side view illustrating another embodiment of a chip with alignment bumps and a substrate will alignment bumps. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The following is intended to provide a detailed description of an example of the invention and should not be taken to be limiting of the invention itself. Rather, any number of variations may fall within the scope of the invention, which is defined in the claims following the description. 
         [0020]    The present invention is a structure and method for fabricating an assembly of two electronic devices that include interconnections to be joined during an assembly of the two devices together to form a composite electronic device. The devices include interconnection pads and/or bumps of solder that when the devices are placed together and reflowed form connections between the devices. Additionally, these devices include bumps or posts that engage with bumps or posts of the other device to provide alignment and lateral stability during assembly. 
         [0021]    As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
         [0022]    Semiconductor integrated circuits or chips are assembled with substrates to produce electronic packages used in electronic products. As discussed, the chip is assembled on a substrate to provide signal connections along with power and ground connections. These assemblies include a Flip-chip Plastic Ball Grid Array where the substrate includes interconnection pads that have presolder or solder on pad (SOP) to provide a solder connection with corresponding interconnection pads of a chip. One method to manufacture the substrate is to screen solder paste through a stencil and then melt the solder to reflow the solder on the substrate interconnection pads. Other methods of substrate manufacture are known by those of skill in the art and may also be used. The resulting solder on the substrate pads form hemispherical domes due to surface tension of the solder when the solder is melted and reforms. When a semiconductor chip, which also has presolder located on its connection pads, is placed onto the substrate, misalignment can occur before or during the assembly and reflow process. The present invention addresses this problem by providing alignment posts or bumps that engage when the chip is placed on the substrate to accurately self-align the chip interconnection pads with the substrate pads during assembly and to prevent the chip from moving sideways relative to the substrate during the assembly and reflow process. 
         [0023]      FIG. 3  is a side view of one of the preferred embodiments of the invention showing a chip  300  having alignment posts  316  and  318  that include solder bumps or domes  320  and  322 . These alignment posts  316  and  318  are copper pillars that are formed on the chip  300  surface along with other interconnection pads such as pad  302  and  306  that also include solder bumps or domes  304  and  308 . Substrate  314  also includes alignment bumps  326  and  328  formed on the substrate  314  along with interconnection bumps such as  310  and  312 . During assembly when chip  300  is placed onto substrate  314 , the alignment post  316  with bump  320  and alignment post  318  with bump  322  engage the substrate  314  alignment bump  326  and alignment bump  328  respectively to align chip  300  interconnection pillars  302  and  306  and their respective bumps  304  and  308  with the substrate  314  interconnection bumps  310  and  312  respectively. This arrangement also prevents sideways motion of the chip relative to the substrate that may occur during the assembly and reflow process. 
         [0024]      FIG. 4  is a side view of another embodiment wherein chip  400  includes alignment posts  416  and  418  having solder bumps  420  and  422  that engage substrate  414  alignment bumps  426  and  428  respectively to align the substrate interconnection bumps such as  410  and  412  with the chip  400  interconnection pillars  402  and  406  with their bumps  404  and  408 . It should be understood with both  FIGS. 3 and 4  that the substrate interconnection bumps may include substrate interconnection pads. 
         [0025]    In one method, the substrate alignment bumps in  FIGS. 3 and 4  are formed by using a stencil or metal mask, such as stainless steel, with openings to form the interconnection pads upon the substrate. Other methods to form bumps known to those of skill in the art may also be used. A screen printing process is used to force solder paste into the stencil openings onto the interconnection pads. The solder paste volume can be controlled by varying the thickness of the stencil and the size of the stencil openings. Also, more presolder can be added to increase thermal cycling fatigue life along with increasing the strength of the bump. Similar techniques can be used in forming bumps on the chip surface. 
         [0026]    In the preferred embodiment illustrated by  FIG. 3 , chip corners are used as the location of the alignment posts such as  316  and  318 . This is shown in  FIG. 5  which illustrates a chip  500  on top of a substrate  560 . For the purposes of this illustration, the chip  500  is only shown with its perimeter  502  and includes the interconnection pillars such as  562  and chip alignment posts  530 ,  534 ,  536 ,  540 ,  544 ,  546 ,  548  and  552  located at the corners of the chip  500 . Also in  FIG. 5 , substrate  560  is shown including interconnection bumps such as bump  560  and alignment bumps  532 ,  538 ,  542  and  550 . Alignment bump  532  will engage alignment posts  530  and  534 . The other alignment bumps  538 ,  542  and  550  with engage alignment posts  536 , 540 ;  544 ,  546 ; and  548  and  552  respectively to assist in the aligning of the chip interconnection pillars such as pillar  562  with the substrate interconnection bumps such as bump  560  during assembly of the chip onto the substrate. Further the substrate alignment bump/chip alignment post corner structure will prevent lateral or sideways motion between the chip  500  and substrate  560 . 
         [0027]      FIG. 6  is a top view arrangement for the assembly in  FIG. 4 . The chip  500  boundary perimeter  602  includes alignment posts  632 ,  638 ,  642  and  650  which engage alignment bump pairs such as  630 ,  634 ;  636 ,  640 ;  644 ,  646 ; and  648 ,  652  respectively to align the chip  600  interconnection pillars such as pillar  662  with the corresponding substrate  660  interconnection bumps  660 . 
         [0028]      FIG. 7  is a top view of another embodiment of the present invention that is an alternative to the four corner structures illustrated in  FIGS. 5 and 6 . In  FIG. 7 , chip  700  with its border perimeter  702  includes interconnection pillars such as interconnection pillar  782  and alignment posts  754  and  762 . Substrate  760  includes interconnection bumps such as interconnection bump  780  and alignment bumps  752 ,  756  and  758  along with alignment bumps  760 ,  764  and  766 . The three alignment bumps  752 ,  756  and  758  engage chip  700  alignment post  754  while the three alignment bumps  760 ,  764  and  766  engage alignment post  762 . Thus  6  alignment bumps rather than 8 alignment bumps in  FIG. 6  would provide alignment and lateral stability. It should be apparent to those of skill in the art that other various combinations of alignment structures on the substrate and the chip would also provide alignment and lateral stability and that these other structures are within the scope of this invention. 
         [0029]    A further embodiment is illustrated in  FIG. 8  which is a side view illustrating a configuration similar to  FIG. 3  except that the chip  800  does not include any pillars. Instead chip  800  includes interconnection bumps such as bumps  802  and  806  that are intended to connect to substrate  814  interconnection bumps  810  and  812  respectively. Chip  800  also includes alignment bumps  816  and  818  which are fabricated to be of a greater height than the chip  800  interconnection bumps such as bumps  802  and  806 . This additional height will assist in alignment during assembly. Substrate  814  includes alignment bumps  826  and  828  that will engage chip  800  alignment bumps  816  and  818  during assembly. In one further embodiment, alignment bumps  826  and  828  are wider than the interconnection substrate bumps such as bumps  810  and  812 . 
         [0030]    The larger volume in height and width of alignment bumps results from additional presolder volume added during fabrication. When the reflow process occurs, the larger size of these alignment bumps will result in these bumps being better to resist fatigue cracking. 
         [0031]    In the embodiments discussed, the alignment posts and alignment bumps are not interconnected to any signal wiring in either the chip or the substrate. However, given their size and sturdiness, these alignment posts and bumps could be interconnected to signals or power or ground connections. 
         [0032]    While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that based upon the teachings herein, that changes and modifications may be made without departing from this invention and its broader aspects. Therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. Furthermore, it is to be understood that the invention is solely defined by the appended claims. It will be understood by those with skill in the art that if a specific number of an introduced claim element is intended, such intent will be explicitly recited in the claim, and in the absence of such recitation no such limitation is present. For non-limiting example, as an aid to understanding, the following appended claims contain usage of the introductory phrases “at least one” and “one or more” to introduce claim elements. However, the use of such phrases should not be construed to imply that the introduction of a claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an”; the same holds true for the use in the claims of definite articles.