Abstract:
A structure and method to improve saw singulation quality and wettability of integrated circuit packages ( 140 ) assembled with lead frames ( 112 ) having half-etched recesses ( 134 ) in leads. A method of manufacturing lead frames includes providing a lead frame strip ( 110 ) having a plurality of lead frames. Each of the lead frames includes a depression ( 130 ) that is at least partially filled with a material ( 400 ) prior to singulating the lead frame strip.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of prior U.S. application Ser. No. 13/537,392, filed Jun. 29, 2012, now U.S. Pat. No. ______. The entire disclosure of U.S. application Ser. No. 13/537,392 is hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    This invention relates generally to semiconductor device packages, and more specifically to leads of flat-pack no-lead semiconductor device packages. 
       RELATED ART 
       [0003]    A semiconductor device may be mounted on a lead frame and encapsulated in a semiconductor device package (hereinafter “package”). A package utilizes leads for externally providing and receiving signals and power. One type of package is a flat-pack no-lead package where the leads are exposed at a bottom and at a side of the package. 
         [0004]    A lead frame strip (hereinafter “strip”) is populated with multiple lead frames. An encapsulating mold compound and portions of the strip between lead frames are cut during singulation of the strip to create individual packages. 
         [0005]    One type of wettable flank of a lead of a flat-pack no-lead package includes a cavity, or recess, on the end of the lead, which has been plated, such as with matte tin, nickel palladium gold or palladium, so that solder can wet to the recess. Flat-pack no-lead packages with wettable flanks have better solder fillet formation and allow for easier visual inspection of a solder joint after surface mounting of the package on a printed circuit board (hereinafter “PCB”). After singulation, a recess of a wettable flank appears as a volume of metal missing from a central area of a bottom, external corner of a lead. A recess is narrower than a lead so as to prevent the mold compound from filling the recess. The wettable flank produces a wettable surface that is higher than a bottom of the package. A fillet is an extension of the solder joint at a side of a package that can be visually inspected. The wettable flank facilitates formation of a fillet. Surface tension causes the solder to wet up into the recess of the wettable flank, and the solder may advantageously form a fillet. 
         [0006]    Typically, two recesses are formed from a depression in a strip. The process of forming a depression is part of a process of forming the lead frames of a strip and is typically done by a lead frame manufacturer. The depression can be created by a partial-etch, or half-etch, process during manufacture of the lead frames. One known depression is shaped as an elongated slot on a bottom surface of a lead of one lead frame and on a bottom surface of a lead of an adjacent lead frame and on a bottom surface of an intermediate portion of the strip between the adjacent lead frames. 
         [0007]    Saw singulation cuts through portions of the strip between lead frames. The cutting process removes, as swarf, much of the intermediate portion of the strip including a middle portion of the depression. End portions of the depression, which remain after saw singulation, become the recesses of the wettable flanks. Most leads are copper. During saw singulation, copper may, due to a ductile nature of copper, disadvantageously fill a portion of the depression that becomes (after singulation) the recess of a wettable flank. The copper may peel when a blade of a saw arrives at an edge of a depression and copper debris may adhere to the edge of the depression. As a result, the copper debris may reduce at least one of the dimensions of the recess. Such reduction in the at least one dimension of the recess is most apparent when the recess was small prior to saw singulation. The lead frame is unsupported at the depression, and, as a result, when the strip is saw singulated, burrs or tear-outs of copper may form, and the depression may capture other saw debris, such as epoxy, from the mold compound. Such copper and other saw debris in the recess of a wettable flank can result in a visual rejection of a package. Also, such copper and other saw debris in the recess of a wettable flank can result in an increased risk of a defect in a solder joint formed during surface mounting of the package to a PCB because such debris may detrimentally affect solder joint formation. Additionally, the debris may fall out of the recess and on to the PCB. 
         [0008]    When the pitch is less than 1 mm, one known method to avoid the debris that may form in recesses of wettable flanks during saw singulation is to punch singulate, rather than to saw singulate, flat-pack no-lead packages. However, punch singulation is disadvantageous because a number of individual units on a strip when a strip is to be punch singulated cannot be as large as a number of individual units on a strip when the strip is to be saw singulated. 
         [0009]    Another known method reduces a rate of sawing and/or uses specialized blades in an attempt to reduce accumulation and retention of debris in recesses; however, such known methods do not eliminate accumulation and retention of debris in recesses. 
         [0010]    Another known method uses a structure that includes a through hole opening in a lead, and then fills the through hole opening with solder prior to singulation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. 
           [0012]      FIG. 1  is a bottom plan view of a portion of a strip including portions of two lead frames, showing depressions in the lead frames. 
           [0013]      FIG. 2  is a cross-sectional taken along line  2 - 2  of  FIG. 1 . 
           [0014]      FIG. 3  is a cross-sectional taken along line  3 - 3  of  FIG. 1 . 
           [0015]      FIG. 4  is a bottom plan view of a portion of the strip of  FIG. 1  after material has been placed into depressions in accordance with various embodiments of the invention. 
           [0016]      FIG. 5  is a cross-sectional taken along cut-line  5 - 5  of  FIG. 4  showing a cross-section of a depression with the material in the depression. 
           [0017]      FIG. 6  is a cross-sectional taken along cut-line  6 - 6  of  FIG. 4  showing a cross-section of a depression with the material in the depression. 
           [0018]      FIG. 7  is a top isometric view of a package produced from a strip similar to the strip of  FIG. 1  when the material in the depressions is a wettable material that is present in depressions during singulation and remains in a recess at an external corner of each lead after singulation, and showing the wettable material in the recess of the external corner of each lead, in accordance with various embodiments of the invention. 
           [0019]      FIG. 8  is a bottom plan view of the semiconductor package of  FIG. 7 . 
           [0020]      FIG. 9  is a perspective view of an enlargement of an encircled region shown in  FIG. 8  showing several recesses and showing the wettable material in the recesses. 
           [0021]      FIG. 10  is a perspective view of an enlargement of an encircled region shown in  FIG. 9  showing one recess and showing the wettable material in the recess. 
           [0022]      FIG. 11  is a partial, side-elevational view illustrating the manner in which the package of  FIGS. 7-10  is mounted to a PCB, and showing a fillet. 
           [0023]      FIG. 12  is a top isometric view of a package produced from a strip similar to the strip of  FIG. 1  when the material in the depressions is a removable material that is present in the depressions during singulation and is removed after singulation, and showing a debris-free recess at an external corner of each lead after the removable material is removed, in accordance with various embodiments of the invention. 
           [0024]      FIG. 13  is a bottom plan view of the package of  FIG. 12 . 
           [0025]      FIG. 14  is a perspective view of an enlargement of an encircled region shown in  FIG. 13  showing several debris-free recesses in accordance with the invention. 
           [0026]      FIG. 15  is a perspective view of an enlargement of an encircled region shown in  FIG. 14  showing one debris-free recess in accordance with the invention. 
           [0027]      FIG. 16  is a perspective view of an enlargement of a prior art recess showing debris in the prior art recess. 
           [0028]      FIG. 17  is a partial, side-elevational view illustration the manner in which a prior art package that includes the prior art recess of  FIG. 16  is mounted to a PCB and shows how formation of a fillet is adversely affected by debris in the prior art recess. 
           [0029]      FIG. 18  is a flow diagram of a method of assembling a flat-pack no-lead package in accordance with one embodiment of the invention. 
           [0030]      FIG. 19  is a flow diagram of a method of assembling a flat-pack no-lead package in accordance with another embodiment of the invention. 
           [0031]      FIG. 20  is plan view of a strip, given by way of example, which may be used in one or more methods of assembling packages in accordance with various embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIG. 1  is a bottom plan view of a portion of a dual, flat-pack no-lead type strip  110  including portions of two adjacent lead frames  112 , showing depressions  130  in each lead frame  112 . Filling the depressions  130  in each lead frame with an appropriate material prior to saw singulation prevents formation and accumulation of debris within recesses of wettable flanks of the leads of each flat-pack no-lead package produced from the strip  110 , thereby facilitating saw singulation and/or allowing a wider process window for saw singulation. The methods in accordance with the invention prevent accumulation of debris in the recesses during assembly of QFN-style packages. Performing saw singulation when material is in the depressions  130  prevents the formation of copper burrs in the recesses. 
         [0033]      FIG. 2  is a cross-sectional taken along line  2 - 2  of the strip  110 . Each lead  120  has a bottom surface  128  and a top surface  226 . 
         [0034]      FIG. 3  is a cross-sectional taken along line  3 - 3  of the strip  110 . 
         [0035]      FIG. 4  is a bottom plan view of the portion of the strip  110  with a material  400  disposed in the depressions  130 . 
         [0036]      FIG. 5  is a cross-sectional taken along cut-line  5 - 5  of the strip  110  showing a cross-section of a depression  130  with the material  400  in the depression. 
         [0037]      FIG. 6  is a cross-sectional taken along cut-line  6 - 6  of the strip  110  showing a cross-section of a depression  130  with the material  400  in the depression. The material  400  is represented by cross hatching in the depressions  130  of  FIGS. 4 ,  5  and  6 . As explained more fully hereinbelow, the material  400  is one of a solder wettable material (hereinafter “wettable material”)  200  and a removable material  300 . 
         [0038]    Each lead frame  112  of the strip  110  includes an outer frame structure  114  that surrounds a centrally positioned opening  116  into which the mold compound, shown diagonally hatched, penetrates during encapsulation. The lead frame  112  may include a die pad  118  disposed within the opening  116 . The successive lead frames  112  of the strip  110  may extend in a two dimensional matrix presenting rows and columns of lead frames. Each lead frame  112  further comprises sets of leads  120  disposed side by side at intervals along respective sides of each lead frame  112  and separated from adjacent lead frames by a gap G. 
         [0039]    Before encapsulation, semiconductor dies (not shown) are mounted on and attached to respective lead frames  112 . Electrical connections are made between bonding pads (not shown) on the die and respective ones of the leads  120  using wires. The lead frames  112  are then encapsulated by applying the mold compound to the strip  110 , either to the entire strip, or to form individual moldings for individual packages. 
         [0040]    Before singulation, as shown in  FIGS. 1 and 4 , the leads  120  are integrally connected to, and supported by, the outer frame structure  114  and extend inward into the opening  116  toward the peripheral edge of the die pad  118 . In each strip  110 , the outer frame structure  114  includes an intermediate common bar  132 , which are common to adjacent lead frames  112 . The outer frame structure  114 , including the common bar  132 , is cut away and discarded during singulation. 
         [0041]    As shown in  FIGS. 1 and 4 , the depressions  130  of the leads  120  of adjacent lead frames  112  within the same column or row, may be formed by semi-etching or partial-etching, which is etching the material of the strip  110  part-way through its thickness. The partial-etching forms partially-etched, elongated depressions  130  extending across the common bar  132  of the outer frame structure  114  common to adjacent lead frames, so that the opposite end portions of the depressions  130  later form (after singulation) recesses  134  at the ends of the juxtaposed leads  120  of the adjacent lead frames. 
         [0042]    A saw street S of the strip  110  extends along the common bar  132 . The passage of a saw blade along each saw street S separates the adjacent lead frames  112  from each other. Orthogonal row and column saw streets S extend within a two-dimensional strip  110 . A width of a blade used in the saw singulation process is such that the saw street S does not include the opposed end portions of each depression  130 . 
         [0043]    Typically, the saw blade is the same width as each of the saw streets S and straddles the common bar  132  of the outer frame structure  114  while it is sawing. Thus, during the saw singulation process, the saw blade cuts along each saw street S longitudinally, cutting into and along the common bar  132  of each outer frame structure  114 , which reduces all the metal material of the common bar  132  to swarf, which is discarded, and further removes or severs a portion of each of the leads  120  to form their outer ends at the peripheral edge surfaces of the package  140 , in addition to cutting the mold compound. The saw singulation process also cuts away the middle portion of depressions  130 . 
         [0044]      FIG. 7  is a top isometric view of a completed quad, flat-pack no-lead package  140  when the material  400  in the partially-etched depressions  130  is the wettable material  200 , which was present in the partially-etched depressions during singulation. The package  140  illustrated in  FIG. 7  was manufactured, or assembled, utilizing a first method (see  FIG. 18 ) in accordance with one embodiment of the invention.  FIG. 7  shows the wettable material  200  in the recess of the external corner of each lead  120  of the package  140 . 
         [0045]      FIG. 8  is a bottom plan view of the package  140 . The wettable material  200  is represented as a small solid dark area in each recess of  FIGS. 7 and 8 . 
         [0046]      FIG. 9  is a perspective view of an enlargement of an encircled region shown in  FIG. 8  showing several recesses  134  and showing the wettable material  200  in the recesses as cross-hatching. 
         [0047]      FIG. 10  is a perspective view of an enlargement of an encircled region shown in  FIG. 9  showing one recess  134  and showing the wettable material  200  in the recess as cross-hatching. 
         [0048]    The package  140  includes a package body (hereinafter “body”)  142  formed by the hardening of electrically insulating plastic encapsulation material, or mold compound, which is applied to a strip such as the strip  110 . Each package  140  comprises sets of discrete, electrical contact elements or leads  120  disposed side by side at intervals along respective sides of the bottom face  146  of the package and extending perpendicularly to the side of the corresponding bottom face  146 . In package  140 , sets of leads  120  are disposed on all four sides of the bottom face  146  and are exposed at the bottom face  146  and at the side edges  150  of the package for soldering to the electrical connections of the support. In a dual no-lead package (not shown), sets of leads  120  are disposed on only two opposed sides of the bottom face  146 . As shown in  FIGS. 7-10 , the ends of the leads  120  of the package  140  terminate approximately flush with the sides of the singulated, completed package. 
         [0049]    The saw singulation process separates the packages  140  from each other by cutting and separating both the individual lead frames  112  of the strip  110  and the plastic encapsulation material in a manner completing the formation of the body  142  of each package  140 . The completely formed package  140  defines a top face  144  and an opposing bottom face  146 , which are generally rectangular. A side edge  150  extends transversely to the top face  144  and bottom face  146  of the body  142 . 
         [0050]    The leads are exposed within the bottom face  146  of the body  142 . The outer ends of the leads  120  are exposed within the side edges  150  of the body  142 . The leads have recesses  134  formed at a corner of each lead  120  formed by the bottom surface  128  of each lead and the exposed outer end of each lead  120  of a package  140 . The bottom surface  128  of each lead near this corner functions as an electrical contact portion of each lead. Completion of the saw singulation process results in a recess  134  being formed within each lead  120 . Each recess  134  is formed in a corner region of the corresponding lead  120  defined by an outer end and the bottom surface  128  thereof. The recess  134  is disposed within the bottom surface  128  and the outer end, but does not extend to the top surface  226  or either of the side surfaces. Each recess  134  has a generally concave configuration. During solder mounting of the package  140  on a PCB  152  (see  FIG. 11 ), solder can reflow up into the recesses  134 . The electrical contact surface portions and outer end, including the recesses  134 , of each lead  120  (which are exposed outside of the body  142 ) may have a plating layer applied to facilitate soldering to the PCB  152 . 
         [0051]    The methods in accordance with the invention overcome the problem of burrs and debris collecting in the recess  134  during saw singulation of packages  140 . The methods in accordance with the invention fill depressions  130  with either the wettable material  200  or with the removable material  300 . The removable material  300  does not compromise the wettability of the lead  120  or of the recess  134 . The removable material  300  has one of rigid and semi-rigid properties when singulation is performed; however, the removable material may be fluidic when it is placed in the depressions  130 . A depression  130  that is at least partially filled with material  400  at time of singulation eliminates (or at least effectively eliminates) debris that would otherwise accumulate in the recesses  134  as a result of singulation, especially saw singulation. Much of the debris that accumulates in the recesses  134  as a result of using known methods of singulation may disadvantageously remain in the recesses indefinitely. The methods in accordance with the invention improve the ability to produce a debris-free recess  134  in packages  140  with fine pitch leads  120  by preventing accumulation of debris in the recess during assembly of the package. The methods in accordance with the invention increases a likelihood of forming an inspectable solder joint after mounting on the PCB  152 . The methods in accordance with the invention fill the depression  130  with a material  400  that is solid enough to prevent formation of burrs, or tear-outs, during, and as a result of, saw singulation. 
         [0052]    A first method in accordance with the invention fills the depressions  130  prior to singulation with the wettable material  200 , which prevents formation and accumulation of burrs and debris during singulation, and does not require removal. With the first method, the depression  130  is at least partially filled with the wettable material  200  such as solder, which is typically tin alloyed with copper, lead, silver or bismuth. In various embodiments, the wettable material  200  is solder, solder paste, tin, bismuth, indium, gold, silver, another wettable material, or combinations thereof. In one embodiment, the solder is SAC305 or SAC405, where S=tin, A=silver and C=copper. For example, SAC305 is 96.5% tin, 3% silver, and 0.5% copper. The depressions  130  may be filled with the wettable material  200  in several ways. The first method fills the depression  130  with the wettable material  200  by squeegee application, stencil print or screen print to move solder paste into the depressions  130 , then reflows the wettable material prior to continuing with normal assembly of the package  140 . In another embodiment, a solder jet is used which streams solder paste through a small nozzle to fill the depressions  130 . In another embodiment, solder paste that has been atomized into nanoparticles is sprayed into the depressions  130 . In another embodiment, solder balls are placed into each depression  130 . The solder balls are then melted or reflowed to fill the depressions  130 . In another embodiment, the strip  110  is masked such that only the depressions  130  are exposed, wherein the wettable material  200  is formed in the openings of a mask. In another embodiment, the strip  110  is plated with the wettable material  200  until the depressions  130  become filled. In some embodiments of the first method, the wettable material  200  that is placed in the depressions  130  is then heated to reflow the wettable material. In each embodiment of the first method, the strip  110  is singulated after the wettable material  200  is placed in the depressions  130 . In each embodiment of the first method, the wettable material  200  is not removed after it is placed in the depressions  130 . Maintaining the wettable material  200  in the depression  130  after singulation prevents any further accumulation of debris in the recess  134  after singulation. 
         [0053]    A second method in accordance with the invention fills the depression  130  prior to singulation with a removable material  300  that can be hard enough to prevent the burrs and debris from collecting in the recess  134 , and that is easily removable using water or other chemistry common to semiconductor processing (such as photo resist). In one embodiment, the removable material  300  one of a hot-water soluble adhesive, a hot-water soluble thermoplastic material and a hot-water soluble thermosetting polymer material. The hot-water soluble material is applied at a high enough temperature (about 100° C.) for the material to be in a liquid form. The hot-water soluble material is adequately solid when cured, but, after it has cured, it rinses cleanly away in hot water. An example of such a hot-water soluble material that can be used is AquaBond® ABS-65 (AquaBond is a trademark of AquaBond Technologies, Inc., of Camarillo, Calif.). In one embodiment, the strip  110  is put into in a bath of the hot-water soluble material at a high enough temperature (about 100° C.) for the material to be in a liquid form. In another embodiment, the hot-water soluble material is heated to a high enough temperature (about 100° C.) for the material to be in a liquid form, and it is applied to the strip  110  by screen printing using a stencil. Then, the hot-water soluble removable material  300  on the strip  110  is allowed to return to room temperature, and the hot-water soluble removable material hardens or solidifies, and it becomes at least semi-rigid. The recesses  134  remain filled with the hot-water soluble removable material  300  during singulation, which prevents debris from entering the recess  134  during the saw singulation process. Next, the partially singulated strip or the individual units are put into a hot-water bath to remove the hot-water soluble removable material  300  from the recess  134 . An exposed debris-free recess  134  results. In one embodiment, the partially singulated strip or the individual units are immersed in hot water or sprayed with hot water (at about 80-90° C.) until the hot-water soluble removable material  300  dissolves. 
         [0054]    The application of the hot-water soluble removable material  300  to the strip  110  is a last step prior to singulation. The immersion of the partially singulated strip or the individual units in hot water, or the spraying the partially singulated strip or the individual units with hot water is a first step after saw singulation. 
         [0055]    In another embodiment, the removable material  300  is a polyvinylpyrrolidone polymer, which is a hot-water soluble thermosetting polymer material that is cured using ultraviolet (UV) light. An example of such a polyvinylpyrrolidone polymer is Dymax® UV Curable Water Soluble Masks 9-20553 Series (Dymax is a trademark of Dymax Corporation of Torrington, Conn.). After the polyvinylpyrrolidone polymer is cured, the strip  110  is singulated. In one embodiment, the strip  110  is partially sawn, thereby producing a partially singulated strip. In another embodiment the strip  110  is sawn through completely, thereby singulating the strip into individual units. After singulation, the partially singulated strip or the individual units are immersed in hot water or sprayed with hot water (at about  120-150° F. ) until the polyvinylpyrrolidone polymer dissolves, thereby removing the polyvinylpyrrolidone polymer from the recess  134 , and revealing a debris-free recess. 
         [0056]    In another method in accordance with the invention, the removable material  300  is polyimide, and the polyimide is removed, using acetone, after singulation, and revealing a recess  134  that is debris-free. 
         [0057]    In various other embodiments, the removable material  300  is another type of polymer, a polymer adhesive, or a photo-resist material, which is then removed after singulation, and revealing a recess  134  that is debris-free. 
         [0058]    In one embodiment, a partial saw procedure is performed on the strip  110  after depositing the removable material  300  to allow for removal of the removable material  300  while the strip is still in strip form. In such one embodiment, the strip  110  is partially sawn, which means sawn entirely through the metal lead frame  112  including through the removable material  300 , but not sawn through the mold compound, thereby producing a partially singulated strip. In such one embodiment, the removable material  300  can be removed from the depressions  130  of the partially singulated strip without debris remaining in the recesses  134  because the metal lead frame  112  has already been cut through and because a primary cause for debris is from cutting of the metal lead frame. The partial saw procedure may use a blade that is slightly wider than a blade used for a through cut to ensure that the metal lead  120  is not accidently “clipped” when full singulation is completed after removing the removable material  300 . In another embodiment the strip  110  is sawn through completely, thereby singulating the strip into fully singulated individual units. 
         [0059]    In each embodiment of the second method, the strip  110  is singulated or partially singulated after the removable material  300  is placed in the depressions  130  and only while the removable material is in the depressions. In each embodiment of the second method, after the strip  110  is singulated or partially singulated, the removable material  300  is removed. 
         [0060]      FIG. 11  is a partial, side-elevational view illustrating the manner in which the package  140  assembled in accordance with one of various embodiments of the invention, is mounted to the PCB  152 , and showing a solder fillet  1100 . The methods (see  FIGS. 18 and 19 ) and the package  140  produced thereby in accordance with various embodiments of the invention aid in the formation of a well-formed solder fillet that can be easily inspected visually. 
         [0061]      FIG. 12  is a top isometric view of a quad, flat-pack no-lead package  140  that was manufactured, or assembled, utilizing the second method (see  FIG. 19 ) in accordance with the invention, in which a strip similar to strip  110  was singulated while the removable material  300  was disposed in the depressions  130 . The removable material  300  was removed after singulation, and, as illustrated in  FIG. 12 , there is a debris-free recess  134  at an external corner of each lead  120 . 
         [0062]      FIG. 13  is a bottom plan view of the package  140 . 
         [0063]      FIG. 14  is a perspective view of an enlargement of an encircled region shown in  FIG. 13  showing several debris-free recesses  134  in accordance with the invention. 
         [0064]      FIG. 15  is a perspective view of an enlargement an encircled region shown in  FIG. 14  showing one debris-free recess  134  in accordance with the invention. The second method (see  FIG. 19 ), and the package  140  produced thereby, results in the debris-free recess  134  shown in  FIG. 15 . 
         [0065]      FIG. 16  is a perspective view of an enlargement of a prior art recess  1634  showing debris  1635  in the prior art recess. 
         [0066]      FIG. 17  is a partial, side-elevational view illustration the manner in which a prior art semiconductor package, which includes a prior art body  1742  and the prior art recess  1634  in a prior art lead  1620 , is mounted to a PCB  1752 , and shows how formation of a prior art solder fillet  1700  is adversely affected by the debris  1635  in the prior art recess. 
         [0067]      FIG. 18  is a flow diagram of a first method of assembling the package  140  in accordance with an embodiment of the invention that utilizes the wettable material  200 . The first method starts with a standard strip  110  that has standard depressions  130  in the lead frames  112 , which depressions are used for creating recesses  134  after singulation. The first method performs standard package assembly up to and including a step of encapsulation of the strip  110  with mold compound. Next, the depressions  130  are filled with the wettable material  200 . Next, the strip  110  is heated so that wettable material  200  reflows, and then, the strip is allowed to cool to room temperature. Next, the strip  110  is singulated. Advantageously, the strip  110  is singulated in a standard way with saw standard blades and techniques, notwithstanding the presence of the wettable material  200  in the depressions  130 . Next, normal assembly is resumed. An end of the first method results in complete package assembly with solder in the recesses  134  of a completed package  140 . 
         [0068]      FIG. 19  is a flow diagram of a second method of assembling the package  140  in accordance with an embodiment of the invention that utilizes the removable material  300 . The second method starts with a standard strip  110  that has standard depressions  130  in the lead frames  112 , which depressions are used for creating recesses  134  after singulation. The second method performs standard package assembly up to and including a step of encapsulation of the strip  110  with mold compound. Next, the depressions  130  are filled with the removable material  300  such as by dipping the strip  110  into in a tank or reservoir of the removable material, or by curtain coating the strip with the removable material, or by stencil printing. Next, the removable material  300  is cured per recommendation of manufacturer of the removable material to make the removable material hard and/or stiff. Next, the strip  110  is singulated using standard singulation techniques, or partial saw singulation is performed on the strip. Advantageously, the strip  110  is singulated in a standard way with saw standard blades and techniques, notwithstanding the presence of the cured removable material  300  in the depressions  130 . Next, the removable material  300  is rinsed or removed from the singulated lead frames  112 . Next, normal assembly is resumed. An end of the second method results in a completed package  140  having debris-free recesses  134 . 
         [0069]    In some embodiments, the depressions  130  are filled with the material  400  after the strip  110  is molded because at this stage, there is very little likelihood of contaminating other portions of the after the strip is molded. By moving wettable material  200  into the depressions  130  after the strip  110  is molded, there is little chance of the wettable material running down inside the lead frames  112  and contaminating wire bonds, die surfaces or die flag attach areas because they are already protected by the molding process. In other embodiments, the depressions  130  are filled at any stage of assembly prior to singulation. 
         [0070]    It has been determined by experimentation that the lead frames  112  can be saw singulated cleanly by proper management of blade loading without melting the material  400  that is disposed within the depressions  130 . 
         [0071]      FIG. 20  is an illustration of one example of a strip such as strip  110 , which may be used in one or more methods of assembling packages  140  in accordance with various embodiments of the invention. The strip illustrated in  FIG. 20  includes three arrays of lead frames, each array including twenty-five lead frames such as lead frame  112 , for a total of seventy-five lead frames. 
         [0072]    In one embodiment, the package  140  is a quad, flat-pack no-lead (QFN) package (hereinafter “QFN-style package”). Examples of QFN-style packages are: a power quad flat-pack no-lead (PQFN) package, an extremely-thin quad flat-pack no-lead (XQFN) package, a depopulated very-thin quad flat-pack no-lead (DQFN) package, and a heatsink very-thin quad flat-pack no-lead (HVQFN) package. QFN-style packages may also include other types of flat-pack no-lead packages. In another embodiment, the package  140  is a dual flat-pack no-lead (DFN) package. 
         [0073]    Although a person of skill in the art will note that  FIGS. 1 and 4  illustrate a strip used in assembling a dual flat-pack no-lead type package, and that  FIGS. 7-9  and  12 - 14  illustrate a quad flat-pack no-lead type package, for ease of description, these will be treated as showing a same product, because the method in accordance with the present invention is applicable equally to both quad and dual flat-pack no-lead type packages. 
         [0074]    The specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. Any benefits, advantages or solutions to problems described herein with regard to specific embodiments are not intended to be construed as a critical, required or essential feature or element of any or all the claims. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. Note that the term “couple” has been used to denote that one or more additional elements may be interposed between two elements that are coupled. 
         [0075]    The Detailed Description section, and not the Abstract section, is intended to be used to interpret the claims. The Abstract section may set forth one or more but not all embodiments of the invention, and the Abstract section is not intended to limit the invention or the claims in any way. 
         [0076]    Although the invention is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below.