Patent Publication Number: US-2002013071-A1

Title: Final testing of IC die in wafer form

Description:
CROSS-REFERENCE TO RELATED DOCUMENTS  
     [0001] The present application is a continuation-in-part (CIP) application to copending patent application Ser. No. 09/625,693, entitled “Method and Apparatus for Protecting and Strengthening Electrical Contact Interfaces”, which was filed on Jul. 26, 2000, and which is incorporated herein in its entirety by reference. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention is in the field of semiconductor and printed-circuit-board (PCB) manufacturing including surface mount technologies (SMT), and pertains more particularly to methods and apparatus for final testing of IC devices.  
       BACKGROUND OF THE INVENTION  
       [0003] The field of integrated circuit interconnection and packaging is one of the most rapidly-evolving technologies associated with semiconductor manufacturing. As demand for devices that are smaller and more powerful continues to increase, pressures are put on manufacturers to develop better and more efficient ways to assemble and package IC products. One of the more recently developed methods for assembling and packaging IC products is known as Ball-Grid-Array (BGA) technology. Motorola™ inc. is one of the noted pioneers of BGA technology. Currently there are many companies that license BGA technology developed by Motorola™, and Motorola and other companies continue to develop BGA technology.  
       [0004] BGA technology provides several advantages over more mainstream technologies such as Fine-Pitch-Technology (FTP), and Pin-Grid-Array (PGA). One obvious advantage is that there are no leads that can be damaged during handling. Another obvious advantage is that the solder balls are typically self-centering on die pads. Still other advantages are smaller size, better thermal and electrical performances, better package yields, and so on.  
       [0005] In BGA technology, wafers or substrates are typically protected with a non-conductive material such as a nitride layer. The die pads are exposed through the nitride layer by means of chemical etching, or by other known methods. The protective nitride layer is intended to protect the substrates from contaminants and damage. One problem with prior-art protective coatings such as a nitride layer is that it is ultra-thin and does not offer any protection to the die pads themselves nor to the connection points between solder balls in the die pads.  
       [0006] It has occurred in the inventor that an additional protective coating, such as a protective polymer-based coating, would offer a measure of protection not provided with prior-art coatings. For example, it is desired that in addition to protecting the substrates itself, die pads and soldered connections may also benefit logically from protection. However, in order to obtain the added, protective benefits from an additional coating, a unique application process must be conceived. It is to such a process that the method and apparatus of the present invention is directed.  
       [0007] In the development of protective coating technology for BGA devices and other contact schemes the inventors have also discovered that a similar technique also provides vastly increased lateral strength for connections made to connection pads on BGA assemblies and other sorts of devices wherein connection extensions to pads are necessary. The unique coatings also provide additional rigidity for devices, both while devices (dies) are still joined on a wafer before separation, and after the die are separated. The inventors have discovered that the benefits of the strengthening are such that silicon thickness can be reduced significantly after the application of such a coating, reducing overall die thickness and also mass, as well as thermal mass.  
       [0008] Another area of IC technology where improvement is wanted, is in the area of final testing of devices. The inventors have discovered that the addition of a protective coating also enables final testing in wafer format, and have provided teaching herein to that end.  
       SUMMARY OF THE INVENTION  
       [0009] In a preferred embodiment of the present invention a method for final testing of IC structures and circuits while in wafer form is provided, comprising the steps of (a) adding first contact extensions to contact pads of individual die implemented on the wafer; (b) covering the pads and contact extensions with a layer of protective material over the frontside of the wafer; (c) removing a portion of the layer of protective material such that a portion of each of the contact extensions is exposed; and (d) final testing die on the wafer by probing the contact extensions with probes of a probe tester, and interacting the die with a test program through the probe tester.  
       [0010] In some cases in this final testing the wafer is moved to reposition the probe tester between tests, and in other the probe may be moved. There are a number of ways a protective coating may be applied to a wafer, including screening, spraying, dispense and spinning, or injection into a mold.  
       [0011] In various embodiments of the present invention taught in enabling detail below, for the first time a method is provided whereby final testing of die while still in wafer form, before separation, is provided, saving much equipment and complicated processing steps. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
     [0012]FIG. 1A is a perspective view of a wafer with die pads according to prior art.  
     [0013]FIG. 1B is an expanded and broken view of the wafer of FIG. 1A illustrating a die-pad exposed through a nitride coating.  
     [0014]FIG. 2 is a broken view of a BGA assembly with a protective overcoat according to an embodiment of the present invention.  
     [0015]FIG. 3A is a plan view of the wafer of FIG. 2 with a protective overcoat applied as a first step according to an embodiment of the present invention.  
     [0016]FIG. 3B is a plan view of the coated wafer of FIG. 3A with coated areas removed in areas to expose the die pads.  
     [0017]FIG. 3C is a plan view of the coated wafer of FIGS. 3A and 3B with solder balls in place according to a third step.  
     [0018]FIG. 4 is a process diagram illustrating processing steps a through e for coating and creating die pad openings according to another embodiment of the present invention.  
     [0019]FIG. 5A is a section view of a vacuum enhanced coating apparatus for applying a protective overcoat to a BGA assembly according to a preferred embodiment of the present invention.  
     [0020]FIG. 5B is a detailed view of a portion of FIG. 5A.  
     [0021]FIG. 6 a - f  illustrates a series of steps in practicing the present invention.  
     [0022]FIG. 7 illustrates a general case of adding contact extensions to contact pads in an embodiment of the present invention.  
     [0023]FIG. 8 a-c illustrates the practical result of backgrinding after adding a protective layer.  
     [0024]FIG. 9 illustrates final testing by probe in an embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0025]FIG. 1A is a idealized perspective view of a coated wafer  9  with die pads  11  according to the prior art art. The skilled artisan will recognize that the pads have been very much exaggerated in this view to be able to provide some detail. In this example of prior art wafer  9  is coated with a thin, protective layer that is nonconductive, such as a nitride layer  13 . Die pads  11  are illustrated in an array on wafer  9 . Typically, die pads  11  are nitride coated along with wafer  9 , which may be a rectangular substrate instead of an actual wafer. After nitride coating, die pads  11  are exposed by such as an etching process.  
     [0026]FIG. 1B is an expanded and broken view of one pad  11  of FIG. 1A, shown in perspective, illustrating the pad exposed through the nitride layer.  
     [0027] In this detail, a die pad  11  can be seen recessed beneath the thickness of nitride coating  13 . It is noted herein, that die pad  11  is completely exposed, meaning that there is no protective layer above any of the land occupied by die pad  11 . When a solder ball (not shown) is placed on die pad  11 , certain real estate of die pad  11  along with the soldered area between the ball and die pad  11  will be exposed, and therefore vulnerable to damage and contamination. A goal of the present invention is to provide a process that according to various embodiments, which are described in enabling detail below, may be used to successfully apply a protective coating layer in addition to the standard hard protective layer such as the nitride layer described above.  
     [0028]FIG. 2 is a broken view of a portion of a BGA assembly  14  with a protective overcoat  17  according to an embodiment of the present invention. In this example of the present invention, BGA assembly  14  exhibits  2  die pads  11  having solder balls  15  adhered thereto. A protective coating  17  is, in a preferred embodiment, a polymer-based coating such as a polyamide coating. In other embodiments, other polymer-based coatings may be used such as are known in the art and available to the inventor. This example illustrates a preferred embodiment, wherein protective coating  17  coats the substrate and the normally exposed area of each die pad  11  around solder balls  15  and also around the perimeter of each solder ball  15 .  
     [0029] A nitride coating  13 , which is illustrated in FIGS. 1A and B, is illustrated here as coating the substrate portion of assembly  14  with the coating extending up over the attached die pads. It may be assumed herein, that a portion of coating  13  has been removed by any one of several known methods in order to clear to an appropriate area on the upper surf aces of each die pad  11  for placement and reflow of solder balls  15 . Protective coating  17  is illustrated as over coating nitride layer  13  and encompassing the lower peripheral areas of solder balls  15 . A height dimension D illustrates the thickness of coating  17 , which may be anywhere from 1 to 3 mils thick in a preferred embodiment. Overcoat  17  functions to protect any exposed pad areas as well as a portion of solder balls  15 .  
     [0030] In practice of the present invention, the inventor has isolated three basic processes that are useful to successfully apply protective coating  17  to BGA assembly  14 . FIG. 3A is a plan-broken view of wafer  14  of FIG. 2 with a protective overcoat applied as a first step according to an embodiment of the present invention. FIG. 3B is a plan-broken view of coated wafer  14  of FIG. 3A undergoing a process to expose covered die pads in a second step. FIG. 3C is a plan-broken view of coated wafer  14  of FIGS. 3A and 3C with solder balls in place according to a third step. The examples of FIG. 3A, 3B, and  3 C illustrate a general 3-part process for the over coating wafer  14 , removing material to expose die pads, and then screening the solder balls into place for a re-flow operation.  
     [0031] Referring now to FIG. 3A, wafer  14  is illustrated with protective coating  17  already applied. It may be assumed herein, although not specifically illustrated, that die pads  11  of FIG. 2 and nitride coating  13  of FIG. 2 are present on wafer  14  before application of protective coating  17 . Coating  17  in a first step completely covers die pads  11  and nitride coating  13 . Coating  17  may be a Polyamide coating or a similar polymer-based coating as described above. Coating  17  may be applied by any one of several processes, such as by vacuum deposition process, a spin-on process, or by virtue of other known methods.  
     [0032] Referring now to FIG. 3B, protective coating  17  is partially removed over the land areas above each die pad attached to wafer  14 . This process may be a laser process, a plasma-etch process, or a chemical-etch process. In both the plasma-etch and chemical-etch processes, a mask is used to protect portions of coating  17  not covering die pads. These portions are represented herein by element number  19 . Areas where material has been removed are represented herein by element number  21 . Once die pads are exposed, they are ready to accept solder balls.  
     [0033] Referring now to FIG. 3C, wafer  14  is illustrated with solder balls  15  screened in place and ready to be re-flowed onto the associated die pads. A re-flow process uses heat to effect the solder connections between balls  15  and associated die pads. The process described above with respect to FIGS.  3 A- 3 C may be used to according to one embodiment, to protect any BGA assembly.  
     [0034]FIG. 4 is a process diagram illustrating processing steps a through e for coating and creating die pad openings according to another embodiment of the present invention. In step a, wafer  14  is coated with a photoresist coating represented herein by element number  23 . As described in FIG. 3A above, it may be assumed that die pads ( 11 ) and a standard nitride layer ( 13 ) are present in this step. This photoresist process may be accomplished using a standard screen-printing technique. It is noted herein that photoresist  23  is applied before applying a protective coating ( 17 ).  
     [0035] In step b, a masking technique is used to cover areas of photoresist that are directly over die pads ( 11 ). Through development of photoresist ( 23 ) with a protective mask applied, resist islands are formed as represented by element number  25  in this step. Resist islands  25  are present areas of photoresist left directly over die pads ( 11 ) after developing.  
     [0036] In step c, protective coating  17  is applied at substantially the same thickness as photoresist  25 . This process of coating fills in the areas inbetween resist islands  25 , such areas representing real estate of wafer  14  not occupied by a die pad ( 11 ).  
     [0037] In step d, a second masking technique is used to protect the areas coated with protective coating  17  in step c. At this point in the process, resist islands  25  are chemically developed, and then etched away exposing associated die pads ( 11 ) leaving all other real estate untouched. In step e, solder balls  15  are screened in place over die pads ( 11 ) as described with reference to FIG. 3C. At this point of the process, a re-flow operation to permanently attach solder balls  15  to die pads ( 11 ) may begin. The process represented herein by FIG. 4, illustrates a process for applying protective coating  17  according to yet another embodiment of the present invention.  
     [0038]FIG. 5A is a section view of a vacuum-application and coating apparatus  27  for applying protective overcoat  17  to a BGA assembly according to a preferred embodiment of the present invention. Vacuum-application and coating apparatus  27 , hereinafter referred to as simply apparatus  27 , is provided and adapted to enable an automated coating process to be performed on a BGA assembly after re-flow. Apparatus  27  comprises an upper plate  29 , a lower plate  31 , and a vacuum seal  33 . In a preferred embodiment both plate  29  and  31  are manufactured of stainless-steel or other durable metals. Plates  29  and  31  may be circular, or rectangular in shape. Other shapes may be employed as well.  
     [0039] In operation a BGA assembly  32 , with solder balls in place, is enclosed by plate  29  and  31  fitted together using a seal  33 . It may be assumed herein that either plate  29  or plate  31  has an o-ring-style groove provided on its mating surface, generally around the perimeter, such that seal  33  may be properly retained and facilitated. In one embodiment, both mating surfaces of plates  29  and  31  may be grooved to facilitate seal  33 . In still another embodiment, a metallic sealing apparatus may be used instead of an o-ring.  
     [0040] Plate  29  and  31  are fitted together over seal  33  to form apparatus  27 , and the plates may be held together by any of several methods, such as by bolts or by clamp mechanisms. A chamber formed within apparatus  27  after assembling contains at least one BGA assembly. In one embodiment, many BGA assemblies may be introduced into the formed chamber for processing. The height of an internal processing area formed within apparatus  27  after assembly is sufficient to accommodate the height of a BGA assembly without damaging the assembly.  
     [0041] Plate  29  has a compliant layer of material, illustrated herein as compliant layer  37  affixed thereto and covering the area over the ball array of an enclosed part. This compliant layer  37  may be a rubberized material, a polymer-based material, or any other suitable material having compliant characteristics. The purpose of compliant layer  37  on plate  29  is to protect the upper portions of solder balls ( 15 ) of a BGA assembly or assemblies inserted into apparatus  27  for processing. The dimensions of the plates are such that, when the plates are closed, the compliant layer forms over the upper portion of each solder ball as may be seen in FIG. 5B.  
     [0042] Upper plate  29  has an injection port  37  provided therethrough, which opens into the vacuum chamber formed within apparatus  27 . Port  37  is adapted to enable injection of an uncured protective coating material  17 , in liquid form, into the vacuum chamber during processing. In one embodiment, there may be more than 1 injection port  37  provided within plate  29 . Lower plate  31  has a vacuum port  35  providing therethrough, which opens into the vacuum chamber formed within apparatus  27 . Port  35  is adapted to connect a vacuum pumping apparatus (not shown) to enable a vacuum to be drawn within apparatus  27 . In one embodiment, there may be more than one vacuum port provided within plate  31 .  
     [0043] In practice of the present invention, at least one BGA assembly complete with re-flowed solder balls is placed onto the surface of plate  3   1 . Plate  29  is urged into to plate  31  over seal  33  and bolted or clamped together with the BGA assembly or assemblies inside. A vacuum is then drawn by virtue of port  35 . The protective coating  17  is injected through port(s)  37  to the internal chamber coating the inserted BGA assembly or assemblies.  
     [0044]FIG. 5B is an expanded view of one edge of the assembly shown in FIG. 5A. In this expanded view, wafer  14  is shown with one solder ball  15 . Compliant layer  37  forms over the top of solder ball  15  and protects the covered area of ball  15  from being coated with injected coating  17 , in a manner that, when released, the solder balls will be exposed on the coated parts. The top surface of solder ball  15  is required to be free of coating as this area is used for lead connection. However, the remaining real estate of wafer  14  and solder ball  15  is covered with protective coating  17  during this back-filling operation after back-filling with the protective coating material in liquid form, the material is cured before the molds are opened.  
     [0045] It will be apparent to one with skill in the art that apparatus  27  may be manufactured of a size such as to facilitate the processing of a number of BGA assemblies simultaneously. In one embodiment apparatus  27  may process only a few assemblies, or perhaps one assembly at a time. Once processing is completed within apparatus  27 , BGA assemblies are removed from apparatus  27  by unbolting or unclamping apparatus and pulling apart plates  29  and  31  revealing completed BGA assemblies. A tracking operation may be used to remove excess coating.  
     [0046] In yet another embodiment of the invention for a method is provided for protecting a BGA assembly in a manner that increased strength is also provided. This method is illustrated herein with the aid of FIGS. 6 a  through  6   f.  FIG. 6 a  illustrates a wafer  41  with balls  45  placed and soldered to solder pads, with a nitride layer  43  in place, as is known in the art. FIG. 6 b  shows the assembly of FIG. 6 a  with a protective layer  47  applied according to embodiments to the present invention as described above. Layer  47  may be applied by screening, spraying, dispense and spinning, by backfilling, or in any of several other ways. Preferably, layer  47  completely covers all balls in the ball grid array.  
     [0047] In FIG. 6 c  a machining operation is illustrated using a grinding or cutting wheel  49  to remove a portion of layer  47  and enough of each ball in the ball grid array that each ball is now exposed as a flat pad even with the upper machined surface of layer  47 . FIG. 6 d  shows the assembly of FIG. 6 c  completely planarized.  
     [0048] After planarization, solder material is applied over each exposed solder ball machined surface. FIG. 6 e  illustrates a solder pad  51  in place over each solder ball in the assembly. Solder islands  51  may be applied by screen printing paste, by plating, or by direct solder ball attachment. Preferably the new solder material may have a melting point equal to that of the original solder balls, or a lower melting point.  
     [0049] After the new solder material is applied, that material is re-flowed, such that the new ball grid array surface is created over the original. The original solder balls are now completely encapsulated in the material of layer  47 , and the original wafer surface and all of the elements of that surface are very well protected. Additionally, the new array is much more robust and strong than the original, because all stress points have now been redistributed away from the wafer surface.  
     [0050] In the embodiments described above, ball-grid-array (BGA) applications have been emphasized and used as examples. The invention in its various aspects, however, has application far beyond BGA assemblies, and is broadly applicable to all situations wherein electrical attachment needs to be made to specific areas on any surface. Attachment by solder balls in BGA technology is described above, but attachment may also be made by other means, such as by wire bonding in many instances. The methods are not limited to wafer and die surfaces, either, and may be applied to printed circuit boards of various kinds and other electronic connection schemes as well.  
     [0051] Broadly speaking, in any case where contact areas are exposed for attaching electrical connections the present invention has application. FIG. 7 illustrates perhaps the broadest case. In FIG. 7 a  surface  53  of a device  55  has one or more connector pad areas  57 , to which electrical connection needs to be made. One such connector area is shown, but there may of course be many more, as in BGA technology. One however, is sufficient to practice the present invention.  
     [0052] In this broad example, pad  57  is typically of a material that can be applied by a deposition technique, and the material that must be used for a connecting extension  59  is typically of a different material. In the case of BGA technology extension  59  is solder material. Because of this, the interface of the two materials at pad  57  is not capable of sustaining significant horizontal stress, and this leads to many physical failures. In the example shown, extension  59  is made just as in the prior art, and may be a solder ball, a gold wire, or some other sort of contact extension.  
     [0053] In the present invention, after contact extension  59  is applied, a polymer protective and strengthening material  61  is applied, which may be done by any one of several methods as have been described in the present application above. Typically material layer  61  is applied to a thickness such that extensions  59  are completely encapsulated, then a removal technique is employed to planarize surface  63 , exposing extension  59  again. The result of this step is a planarized surface  63  with new contact areas  65 .  
     [0054] In a final step a new contact extension  67  added to contact area  65 , and this extension can now typically be of the same material as extension  59 , such that the juncture at area  65  may be of contiguous material, making a very strong juncture, as opposed to the weak juncture at pad  57 . The weak juncture at pad  57 , however, is now encapsulated by layer  61 , and thus greatly strengthened.  
     [0055] In summary, by adding an extension to pads  57 , even though the interface between the extension and the pad may be fairly weak, then adding a polymer layer  61  the weak juncture can be strengthened. Then new extensions can be added with an interface that is much stronger then the original, providing thereby a very much more durable mechanism, while at the same time protecting the original surface and interfaces from environmental effects.  
     Improving Strength While Reducing Thickness and Mass  
     [0056] In another aspect of the present invention a method and apparatus is provided wherein integrated circuits may be improved in electrical characteristics and at the same time reduced in overall thickness and mass without sacrificing strength or integrity.  
     [0057] Referring now to FIGS. 6 a  through  6   f,  which show the progression of steps in a preferred embodiment for adding a protective layer to a wafer having devices implemented thereon, attention is once again drawn to the fact of adding a polymer layer to an IC wafer after extending contact regions away from the top surface of the wafer. As was previously described, the polymer layer, having been applied in a preferred embodiment to a thickness greater than the height of the contact extensions, as shown in FIG. 6 b,  may be planarized in any of a number of ways, such as by machining, exposing a portion of each of the contact extensions, to which electrical contact may subsequently be made. The general process of planarizing by machining is illustrated in FIG. 6 c,  and a planarized wafer in section is shown in FIG. 6 d.    
     [0058] As was described above, the materials at the surface of a wafer, to which a contact extension may be joined, are typically different than the materials that are desirable for making such an extension, such as solder balls for example, in the processes classed as ball-grid array (BGA) processes. The natural result is that the integrity of the original interface between a contact pad and the extension material is relatively low. That is, there is typically little lateral or vertical strength in such joints, and the resulting system is subject to deterioration and damage from many different causes and directions. For example, rough handling, vibration, and the like.  
     [0059] It was described above in preferred embodiments how the polymer layer, encapsulating the original interface of a contact extension, such as a solder ball, to a contact region on a die on a wafer, stabilizes and increases the strength of the original joint, as well as providing environmental protection for the circuitry in dies on a wafer. After planarizing a new contact extension can be made, typically using the same material as the first extension, providing a very strong and sure joint, because, for one reason, the joint can be contiguous. That is, in joining solder to solder, for example, there will be no dissimilar-material interface, but a continuous solder joint.  
     [0060] In a new aspect of the invention it is recognized that the polymer layer provides even more strengthening than was previously described. The polymer may be of a material having considerable strength when cured, and thus stiffens the wafer substantially. It is well known that silicon as used in wafers for IC manufacture is a brittle and vulnerable material. Not so the polymers that may be used for adding a protective layer in embodiments of the present invention.  
     [0061] The result of adding a polymer coating is that a wafer or die with the added coating is significantly stronger and more resilient than the substantially silicon-alone original structure. As a result one may backgrind such wafers to reduce the overall thickness of the die without sacrificing strength and endurance of the structure. Reducing the relative thickness of the silicon portion of the resulting overall structure by such backgrinding also has a beneficial effect of improving the electrical characteristics of the integrated circuits, because silicon is a poor conductor. The reduced thickness also provides a structure with significantly reduced thermal mass.  
     [0062]FIGS. 8 a  through  8   c  illustrate the steps and practical result of backgrinding after adding a polymer layer. FIG. 8 a  shows a section through a wafer  40  having contact extensions  45  added and a polymer coating  47  completed according to an embodiment of the present invention. The wafer with all added elements has an overall thickness T and a thickness t for the silicon portion. FIG. 8 b  shows a grinding process in progress by which the wafer is reduced in thickness by grinding away a significant portion of the silicon portion from the backside, using a grinding wheel  49 .  
     [0063]FIG. 8 c  shows the wafer after backgrinding, which now has an overall thickness T and a thickness for the silicon portion of t. In this example the overall thickness is reduced to less than {fraction (1/4 )} of its former thickness, and the thickness of the silicon (t) is now less than the thickness of the added polymer layer. This is possible because the polymer layer is a cross-linking material when it cures, unlike the single crystal silicon, and the polymer layer is quite a lot stronger in every direction than the silicon.  
     [0064] A practical result of such backgrinding according to the present invention is that overall weight is reduced, thermal mass is reduced, cooling of dies in operation from the backside is now easier because the thermal thickness of the wafer is reduced, and the die or wafer is still stronger than it was before the addition of the polymer layer, and better able to endure rough handling and shock.  
     Final Testing of IC Die in Wafer Form  
     [0065] Final testing of finished IC dies is a process very well-known in the art. As is known in the art, there are a number of ways dies are finished; that is, provided with means to be operated by interconnection with external circuitry. As one example, dies are separated from the wafer upon which they are created, and then bonded to lead frames. Fine wires are bonded to the interface pads on the die and also to extensions of the lead frame. Each die is then encapsulated in a polymer material and each encapsulated assembly is trimmed from the lead frame. A portion of the lead frames provide strong conductors extending outside the encapsulation material for use in soldering the assembly to such as a printed circuit board.  
     [0066] In another example solder balls are bonded to contact pads of each die, and these solder balls are then the contact interface to other circuitry. This practice is described in some detail in this disclosure, and is well-known in the art as Ball Grid Array (B GA) technology.  
     [0067] In any case, final testing, which must always be done before ICs are delivered to customers, is done after the die are separated from the wafer. Although some very limited circuit testing is done in wafer form by what is known as Probe Testing, the complicated final testing cannot be done at this point, because the contacts pads on the die on the wafer cannot support the mechanical consequences of probe testing. Further, the final testing that is done conventionally requires complicated robotic equipment for handling the individual finished die packages and making the necessary contacts for the testing to occur.  
     [0068] In an embodiment of the present invention final testing of die functions is performed on die before die separation from the wafer and final packaging. The added strength and integrity provided by the unique protective polymer layer makes this possible and practical.  
     [0069]FIG. 9 a  is a simplified diagram of a wafer  40  upon which a plurality of dies (ICs) have been formed, as is known in the art. As the die are not at this point separated from the wafer, two die are indicated by element numbers  69  and  71 , each having two contacts points,  73  and  75  for die  69 , and  77  and  79  for die  71 . There are, of course, many more contacts than those shown, and the elements are not shown in scale in FIG. 9 a.    
     [0070] In FIG. 9 a  contact regions  73 ,  75 ,  77 , and  79  are the exposed regions of contact extensions added to wafer  40  and exposed in the planarizing process performed on polymer layer  47 . Also as previously described, the polymer material is by nature much stronger than the silicon material, and provides lateral support for the interfaces between the contact extensions added and the original contacts to IC devices on the wafer.  
     [0071] In FIG. 9 a  a probe device  81  is indicated as having probes  83  and  85  in contact with contact regions  77  and  79 , and having a connection to testing apparatus. The drawing is representative only, and it will apparent to the skilled artisan that the probe apparatus may in fact have many more probe extensions, and there are many ways, known in the art, that probe apparatus may be implemented.  
     [0072] The issue in the present embodiment is that polymer layer  47  stiffens and strengthens the wafer assembly, and provides contact pads supported by the added polymer layer such that the action of the probe does not damage the surface of the wafer or any of the structures of die on the wafer, and now final testing of the die may be done before separation of the die from the wafer.  
     [0073] In another embodiment the probe apparatus is not limited to a single die as indicated in FIG. 9, but may have probe extensions for testing multiple dies at the same time. Further, the wafer may be translated in any direction to reposition die for testing, or the probe apparatus may be moved laterally in any direction between tests to reposition for testing as yet untested die on the wafer.  
     [0074] Testing by probe for final testing of all functions of die while the die are still a part of the wafer eliminated many steps that are otherwise necessary, such as handling finished and packaged ICs in a testing process after the die are separated from the wafer, and eliminates a need for ever performing the packaging and finishing tests for those die that do not pass the final testing in the wafer form.  
     [0075] It will be apparent to one with skill in the art that the method and apparatus of the present invention may be provided for a wide variety of shapes and sizes of BGA assemblies and other assemblies without departing from the spirit and scope of the present invention. Similarly, the method and apparatus of the present invention may be applied to BGA assemblies of varying materials. The method and apparatus of the present invention provides an automated and efficient way to apply an additional protective coating to BGA assemblies. Further, in some aspects the thickness and bulk may be significantly reduced, and the way that material is removed may vary widely. In still other aspects final testing may be done in a wide variety of ways. Hence he method and apparatus of the present invention should be afforded the broadest scope possible under examination. The spirit and scope of the present invention should be limited only by the claims that follow.