Abstract:
A method of making electronic packages includes providing a leadframe strip that includes a plurality of leadframes, wherein the leadframes comprise a plurality of leads, etching a surface of each of the leadframes to form an opening, wherein each of the leads has a lead tip that connects to a die paddle within the opening, isolating each of the leads from the die paddle, adhering a tape to a bottom side of the leadframe strips, leads, and die paddle, attaching a die to the die paddle, placing ball bumps on each of the lead tips, and connecting the die to the ball bumps. The electronic package includes a leadframe having a plurality of leads, wherein each of the leads has a lead tip, an opening formed within the leadframe, a die paddle that is disposed within the opening and is isolated from each of the lead tips, a tape that is adhered to a back side of the leadframe, leads, and die paddle, and a die, wherein the die is attached to the die paddle and is connected by wires to a bump disposed on each of the lead tips.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to Malaysia Application No. PI 20071214, filed Jul. 25, 2007, which is incorporated by reference in its entirety for all purposes. 
     BACKGROUND OF THE INVENTION 
     As electronic devices become smaller, the electronic packages that make up the electronic devices have become smaller. As such, manufacturers are constantly searching for ways to make thinner packages. They often try to reduce the size or thickness of the packaging components. To this end, manufacturers also may try to eliminate packaging components by modifying and utilizing other components more efficiently. Currently manufacturers have developed package designs and corresponding manufacturing methods, in which the package thickness has reached 0.3 mm. 
     However, to produce smaller and thinner packages is challenging because there are components that are deemed to be essential for packaging and cannot be eliminated. In addition, to manufacture smaller packages the packaging technology and process may need to be altered substantially, thereby adding to the manufacturing costs. As such, there is a need for a smaller and thinner package design and a method to manufacture the same, especially to achieve a package thickness of 0.2 mm or less. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide systems and methods that use a leadframe as the main structure of the package so that the leadframe thickness is the thickness of the package. Embodiments of the present invention also provide methods of achieving a 0.2 mm thin plastic leadless package with an exposed metal die paddle (exposed heatsink). 
     In one embodiment of the present invention, a method of making packages includes providing a leadframe strip having a plurality of leadframes, wherein the leadframes have a plurality of leads, etching a surface of each of the leadframes to form an opening, wherein each of the leads has a lead tip that connects to a die paddle within the opening, isolating each of the leads from the die paddle, adhering a tape to a bottom side of the leadframe strips, leads, and die paddle, attaching a die to the die paddle, placing ball bumps on each of the lead tips, and connecting the die to the ball bumps. 
     In another embodiment of the present invention, molded ribs are formed on the leadframe strips. 
     In yet another embodiment of the present invention, the method includes creating a mold cap over the opening, thereby encapsulating the die. 
     In yet another embodiment of the present invention, the method includes singulating the leadframe strips. 
     In yet another embodiment of the present invention, the method includes applying a layer of epoxy to a back side of the die, and placing the back side of the die on top of the die paddle. 
     In yet another embodiment of the present invention, the method of connection is done by wire-bonding. 
     In yet another embodiment of the present invention, the method further includes coating the leadframe strip with NiPdAu. 
     In another embodiment of the present invention, an electronic package includes a leadframe having a plurality of leads, wherein each of the leads has a lead tip, an opening formed within the leadframe, a die paddle that is disposed within the opening and is isolated from each of the lead tips, a tape that is adhered to a back side of the leadframe, leads, and die paddle, and a die, wherein the die is attached to the die paddle and is connected by wires to a bump disposed on each of the lead tips. 
     In yet another embodiment of the present invention, the electronic package further includes a mold cover that encapsulates the opening. 
     In yet another embodiment of the present invention, the mold cover of the electronic package is selected from a group consisting of flushed mold cap, raised flat mold cap, and dome-shaped mold cap. 
     In yet another embodiment of the present invention, the opening of the electronic package has a predetermined depth. 
     In yet another embodiment of the present invention, the die paddle of the electronic package has a thickness that is smaller than the predetermined depth of the opening, and is configured to fit within the opening. 
     In yet another embodiment of the present invention, the die of the electronic package has a thickness that is smaller than the predetermined depth of the opening, and is configured to fit within the opening after attachment to the die paddle. 
     In yet another embodiment of the present invention, the lead tip of the electronic package includes metal and a thickness that is less than 0.025 mm. 
     In yet another embodiment of the present invention, the leadframe includes a leadframe strip coated with NiPdAu. 
     In another embodiment of the present invention, a method of making packages includes providing a leadframe strip that includes a plurality of leadframes, wherein the leadframes include a plurality of leads, etching a surface of each of the leadframes to form an opening, wherein each of the leads has a lead tip that connects to a die paddle within the opening, isolating each of the leads from the die paddle, removing the die paddle, adhering a tape to a bottom side of the leadframe strips and leads, and attaching a flip chip to each of the lead tips. The method can further include coating the leadframe strip with NiPdAu. 
     In yet another embodiment of the present invention, the method includes connecting a plurality of metal bumps from the flip chip to each of the lead tips. 
     In yet another embodiment of the present invention, the method further includes providing molded ribs to the leadframe strips. 
     In yet another embodiment of the present invention, the method includes creating a mold cap over the opening, thereby encapsulating the die. 
     In another embodiment of the present invention, an electronic package includes a leadframe having a plurality of leads, wherein each of the leads has a lead tip, an opening formed within the leadframe, a tape that is adhered to a back side of the leadframe and leads, and a flip chip, wherein the flip chip includes a plurality of metal bumps and is connected with each of the lead tips through the each of the metal bumps. The leadframe of the electronic package can also include a leadframe strip coated with NiPdAu. 
     In yet another embodiment of the present invention, the electronic package further includes a mold cover that encapsulates the opening. 
     In yet another embodiment of the present invention, the mold cover of the electronic package is selected from a group consisting of flushed mold cap, raised flat mold cap, and dome-shaped mold cap. 
     In yet another embodiment of the present invention, the opening of the electronic package has a predetermined depth. 
     In yet another embodiment of the present invention, the flip chip connected to the electronic package has a thickness that is smaller than the predetermined depth of the opening, and is configured to fit within the opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description and the accompanying drawings, which illustrate examples of the invention. 
         FIG. 1  is an illustration of a raw leadframe copper blank strip. 
         FIG. 2  is an illustration of a leadframe strip. 
         FIG. 3  is a plan view individual leadframe pattern design is critical to achieve the desired result of a thin leadless package. 
         FIG. 4  is a three-dimensional view of a thin leadless package. 
         FIG. 5  is a cross section view of the individual leadframe illustrated in  FIG. 4  after etching, in accordance with one embodiment of the invention. 
         FIG. 6  is a plan view of the individual leadframe illustrated in  FIG. 5  before isolation, in accordance with one embodiment of the invention. 
         FIG. 7  is a plan view of the individual leadframe illustrated in  FIG. 6  after lead isolation, in accordance with one embodiment of the invention. 
         FIG. 8  is a three-dimensional view of the individual leadframe illustrated in  FIG. 7  after lead isolation, in accordance with one embodiment of the invention. 
         FIG. 9  is a three-dimensional view of the individual leadframe illustrated in  FIG. 8  after die paddle removal, in accordance with one embodiment of the invention. 
         FIG. 10  is a bottom view of a leadframe strip that is taped with polymide tape or equivalent, in accordance with one embodiment of the invention. 
         FIG. 11  is a cross section view of individual leadframe after taping with lead isolation, in accordance with one embodiment of the invention. 
         FIG. 12  is a cross section view of individual leadframe after taping with lead isolation with the die paddle removed, in accordance with one embodiment of the invention. 
         FIG. 13  is a plan view of leadframe strip with molded ribs, in accordance with one embodiment of the invention. 
         FIG. 14  is a cross section view of individual leadframe with a chip attached, in accordance with one embodiment of the invention. 
         FIG. 15  is a cross section view of an individual leadframe with ball bumps on lead tips, in accordance with one embodiment of the invention. 
         FIG. 16  is a plan view of an individual leadframe with ball bumps on lead tips, in accordance with one embodiment of the invention. 
         FIG. 17  is a plan view of an individual leadframe with a chip that is wire connecting to the lead tips, in accordance with one embodiment of the invention. 
         FIG. 18  is a cross section view of an individual leadframe with a chip that is wire connected to the lead tips, in accordance with one embodiment of the invention. 
         FIG. 19  is a plan view of an individual leadframe with wires connecting the chip to the lead tips, in accordance with one embodiment of the invention. 
         FIG. 20  is a cross section view of individual leadframe after flip chip, in accordance with one embodiment of the invention. 
         FIG. 21  is a cross section view of an individual leadframe after encapsulation, in accordance with one embodiment of the invention. 
         FIG. 22  is a three-dimensional view of an individual leadframe after encapsulation, in accordance with one embodiment of the invention. 
         FIG. 23  is a cross section view of an individual leadframe with raised flat mold cap, in accordance with one embodiment of the invention. 
         FIG. 24  is a three-dimensional view of an individual leadframe with raised flat mold cap, in accordance with one embodiment of the invention. 
         FIG. 25  is a cross section view of an individual leadframe with a dome shape mold cap, in accordance with one embodiment of the invention. 
         FIG. 26  is a three-dimensional view of an individual leadframe with a dome shape mold cap, in accordance with one embodiment of the invention. 
         FIG. 27  is a three-dimensional view of an individual leadframe lead cut, in accordance with one embodiment of the invention. 
         FIG. 28  is a three-dimensional view of an individual leadframe singulated, in accordance with one embodiment of the invention. 
         FIG. 29  is a top three-dimensional view of a singulated unit, in accordance with one embodiment of the invention. 
         FIG. 30  is a bottom three-dimensional view of a singulated unit, in accordance with one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general the present invention provides a package design and a method of manufacturing the same that provide a leadless package and reduce the thickness of the package. The embodiments of the present invention are implemented in a manner that utilizes the existing leadframe base technology, in which manufacturing can be done more efficiently, while also providing an exposed heatsink through the exposed metal die paddle. Embodiments of the present invention are sufficiently flexible for use with wire-bonded die and flip chips. As one of skill in the art will appreciate, the embodiments described herein are exemplary, and other embodiments are possible. Like reference numerals refer to the same item in different figures. 
       FIG. 1  is an illustration of a raw leadframe copper blank strip  10 , with a given length  12 , width  14 , and thickness  16 . The copper blank strip  10  is the starting point in the manufacture of a leadframe (not shown here). The length  12  and width  14  of the leadframe copper blank strip is flexible and is determined by production requirement. The thickness  16  of the leadframe copper blank strip can be of any desired size, as this will determine the minimum thickness of the finished product, which is the package. In a preferred embodiment, the thickness  16  is 0.2 mm. However, it should be appreciated that a thinner leadframe copper blank strip can be used if a thinner package of less than 0.2 mm is required. 
       FIG. 2  is an illustration of a leadframe strip  20 . The leadframe strip  20  comprises multiple leadframes  22 . Each leadframe  22  has a particular pattern, in which the individual leadframe pattern will be etched out from the raw leadframe copper blank strip  10  in a single etch step. Additionally the leadframes  22  can be arranged in a pattern that maximizes the number of leadframes  22  that fit into the leadframe  20  and that can be processed with existing equipment. In one such arrangement the leadframes are positioned in a matrix array. In the preferred embodiment, the leadframe copper blank strip  10  will be in a reel during processing and upon completion the blank  10  will be cut to the required length  12 . In other embodiments the leadframes can be cut out of the copper blanks during the reel processing. 
       FIG. 3  is a plan view of the individual leadframe  22  described in  FIG. 2 . The individual leadframe pattern design is used to achieve the desired result of a thin leadless package. The leadframe  22  is made of a plurality of individual leads  32 . The number of individual leads  32  can vary depending on the application. 
       FIG. 4  is a three-dimensional view of a thin leadless package that has been etched to have a recessed region to position a die. By etching the leadframe  22 , the resulting pattern will provide a metal die paddle  42 , in which the die paddle  42  serves as a platform for attaching the chip, or die (not shown). The recessed region or die paddle can be formed by various application such dry etching or wet etching. In this embodiment, the metal die paddle  42  is joined to the individual leads  32 . The metal die paddle  42  provides a heat sink since it is exposed and facilitates wire connection (e.g., gold or copper) from the chip to the leads  32 , which are also exposed metal pads. For flip chip connection, the chip (die) will connect directly to the leads  32  thru metal bumps (not shown). 
       FIG. 5  is a cross-sectional view of the individual leadframe  22  illustrated in  FIG. 4  after etching, in accordance with one embodiment of the invention. In the preferred embodiment, the area of the individual leadframe  22  that makes up the metal die paddle  42  and the individual leads  32  is etched so that a metal thickness less than 25 microns remains after etching. At this stage, the leadframe strip  20  is also plated with NiPdAu or equivalent material to prepare the areas making up the metal die paddle  42  and the individual leads  32  for the eventual chip connection. In one embodiment the individual leadframe  22  is etched so that the round corner is formed between the die paddle  42  and the individual lead  32 , as illustrated. In another embodiment a sharp inside edge is formed between the die paddle and the individual lead  32  (not shown). The view along A-A′ is illustrated in  FIG. 6 . 
       FIGS. 6-13  illustrate leadframe preparation prior to assembly. 
       FIG. 6  is a plan view of the individual leadframe  22  illustrated in  FIG. 5  before isolation, in accordance with one embodiment of the invention. At this point, the leadframe  22  has been etched and plated as described above. The cross section of this plan view is illustrated in  FIG. 5  and the view along line A-A′ is depicted. 
       FIG. 7  is a plan view of the individual leadframe  22  illustrated in  FIG. 6  after lead isolation, in accordance with one embodiment of the invention. A tool is used to isolate the leads  32  from the die paddle  42  or to remove the die paddle  42  completely for flip chip attachment. The tool mechanically punches out the metal between the leads  32  and the die paddle  42 . The tool is also used to define the exposed lead length and the exposed die paddle  42  of the package. 
     Although the operations illustrated in  FIGS. 1-7  can be performed as part of the lead frame packaging process, these operations can also be performed by a leadframe supplier so that leadframes with the described shape are sent to the packaging operations prepared for subsequent chip assembly. 
       FIG. 8  is a three-dimensional view of the individual leadframe illustrated in  FIG. 7  after lead isolation, in accordance with one embodiment of the invention. 
       FIG. 9  is a three-dimensional view of the individual leadframe illustrated in  FIG. 8  after die paddle removal, in accordance with one embodiment of the present invention. 
       FIG. 10  is a bottom view of the leadframe strip  20  after the lead isolation. In this embodiment of the present invention, the bottom of the leadframe strip  20  is taped with polymide tape  102 , or equivalent type of material, where the exposed leads  32  (metal pad) and exposed die paddle  42 .  FIGS. 11-12  illustrate further details of the polymide tape  102  attached to the leadframe strip  20 . 
       FIG. 11  is a cross-sectional view of individual leadframe  22  after lead isolation and taping, in accordance with an embodiment of the present invention. In one embodiment of the invention, a tape  102  is attached to the bottom of the leadframe  22  before the die paddle  42  is removed. The tape  102  can be used to support the leads from being damaged in subsequent processes. Supporting the leads with tape  102  can be advantages in applications where the leads are flimsy after they have been isolated in the lead isolation process. 
       FIG. 12  is a cross section view of individual leadframe  22  after lead isolation and taping with the die paddle removed, in accordance with an embodiment of the present invention. In this embodiment, the die paddle  42  is first removed from the leadframe  22  and then the tape  102  is applied to the bottom of the leadframe  22 . As with the embodiment illustrated in  FIG. 11 , the tape  102  can be used to support the leads from being damaged in subsequent processes. As described above with reference to  FIG. 11 , supporting the leads with tape  102  can be advantages in applications where the leads are flimsy after they have been isolated in the lead isolation process. 
       FIG. 13  is a plan view of leadframe strip  20 , in accordance with another embodiment of the present invention. The leadframe strip  20  has molded ribs  132  along the sides to add rigidity to its overall structure. This step of adding molded ribs is optional, depending on the leadframe strip rigidity requirements. This step would involve molding plastic ribs on strategic locations on the leadframe strip. 
       FIGS. 14-29  illustrate the assembly of the leadframe. 
       FIG. 14  is a cross-sectional view of individual leadframe  22  with a chip  142  attached, in accordance with an embodiment of the present invention. A layer of conductive epoxy  144  (or like adhesive material) is applied to the backside of the chip (or die)  142  to affix it  142  to the die paddle  42 . The epoxy  144  can be in the form of a film or can be screen printed onto the die paddle  42 , so that the epoxy bond line thickness can be better controlled, thereby controlling the overall height of the package. The chip (die)  142  is then picked and placed onto the die paddle of the individual leadframe using die bonder equipment. This arrangement is to set up electrical connection between the chip  142  and lead tips  146  of the individual leads, and this arrangement will be further described in connection with  FIG. 18 . 
     In one embodiment, the present invention can be used to manufacture a package that has a thickness of 0.2 mm or less. To meet this requirement, the chip (die) needs to be processed to a maximum thickness of 0.050 mm. 
       FIG. 15  is a cross-sectional view of an individual leadframe  22  with ball bumps  152  on lead tips  146 , in accordance with another embodiment of the invention. The addition of ball bumps  152  to the lead tips  146  depends on the flatness of the lead tip surface for wire bonding. In other words, the addition of the ball bumps  152  is optional. Ball bumps  152  are placed on the lead tips  146  using wire bonding machine to provide a flat surface for subsequent wire connection between the chip  142  and the leads  32 . Ball bumps  152  can be made of different materials such as gold or copper. 
       FIG. 16  is a plan view of an individual leadframe  22  with ball bumps  152  on lead tips  146  located on individual leads  32 , in accordance with one embodiment of the present invention. 
       FIG. 17  is a plan view of an individual leadframe  22  with a chip  142  that is wire-connected to the lead tips  146 , in accordance with another embodiment of the invention. The wire  172  is used to facilitate electrical connection between the chip  142  and the lead tips  146 . The wire  172  is connected via the wire-bonding process. Depending on the application, the wire is preferably gold and can also be aluminum. Either a ball or a stitch is placed on the ball bump during the wire-bonding process depending on the mode of bonding to achieve a minimum loop height. In this embodiment, one end of the wire  172  is connected to the chip  142  through a ball bump while the other end of the wire is connected to the lead tips  146  through a stitch bond  182  placed on each of the ball bumps  152  during the wire-bonding process. 
       FIG. 18  is a cross-sectional view of an individual leadframe  22  with a chip  142  that is wire-connected to the lead tips  146  through the ball bumps  152 , in accordance with an embodiment of the present invention. As with the embodiment illustrated in  FIG. 17 , the wire  172  is used to facilitate electrical connection between the chip  142  and the lead tips  146 , and it  172  is connected via the wire-bonding process. Depending on the application, the wire is preferably gold or copper and can also be aluminum. Either a ball or a stitch is placed on the ball bump during the wire-bonding process depending on the mode of bonding to achieve a minimum loop height.  FIG. 18  shows an embodiment in which an additional ball bump  152 A is placed on the chip and a ball  174  is used and placed on each of the ball bumps  152  while the other end of the wire is connected to the chip through a stitch bond  182  placed on each ball bump  152 A during wire-bonding.  FIGS. 18 ,  21 ,  23 , and  25  illustrate additional embodiments that include ball bump  152 A and stitch bond  182 . 
       FIG. 19  is a plan view of an individual leadframe  22  with wires  172  connecting the chip  142  to the lead tips  146 , in accordance with one embodiment of the present invention. The wires  172  are connected via wire bonding to the ball bumps  152  on lead tips  146  of the individual leads  32  as described above with reference to  FIGS. 17 and 18 . 
       FIG. 20  is a cross-sectional view of an individual leadframe  22  after flip chip attachment, in accordance with another embodiment of the invention. When attaching a flip chip  192 , it preferably uses a leadframe  22  with the die paddle  42  removed, as described in connection with  FIGS. 9 and 12 . The flip chip  192  is bonded to the lead tips  146  through its metal bumps  194  with the use of a flip chip bonder. The metal bump, which can be gold or copper, can be applied by thermo-sonic bonding or reflow with solder paste. 
       FIG. 21  is a cross-sectional view of an individual leadframe  22  after encapsulation, in accordance with yet another embodiment of the present invention. The chip (die)  142  and wires  172  are then protected from the environment by encapsulating the chip  142  and the wires  172  with a liquid mold compound. (In an alternative embodiment, the flip chip  192  and its metal bumps  194  can be encapsulated with the same type of liquid mold compound for environmental protection.) A black or clear liquid mold compound can be used depending on the application. For example, a clear liquid mold compound will be used for an optical application. After the liquid mold compound dries and solidifies, it becomes a mold cap  202 .  FIG. 21  shows the mold cap  202  that is flushed with the top  204  of the leadframe  22 . This embodiment is best suited for manufacturing the thinnest possible package, such as one that has a thickness of 0.2 mm or less. It should be appreciated that the mold cap  202  can be in different thicknesses and configuration as will be described in  FIGS. 23-26 . 
       FIG. 22  is a three-dimensional view of an individual leadframe  22  after encapsulation, in accordance with an embodiment of the present invention. 
       FIG. 23  is a cross-sectional view of an individual leadframe  22  with a raised flat mold cap  222 , in accordance with one embodiment of the present invention. The raised flat mold cap  222  is raised over the top of the leadframe  22 . The raised flat mold cap  222  is suitable to create packages that are thicker, such as one that has a thickness greater than 0.2 mm. For example, this embodiment may be useful when the chip (die)  142  is thicker. This embodiment provides some flexibility in applications where the chip (die)  142  thickness is more than 0.050 mm but less than 0.100 mm. In these applications the mold cap can be raised by 0.050 mm. 
       FIG. 24  is a three-dimensional view of an individual leadframe  22  with raised flat mold cap  222 , in accordance with an embodiment of the present invention. 
       FIG. 25  is a cross-sectional view of an individual leadframe  22  with a dome-shaped mold cap  242 , in accordance with another embodiment of the present invention. The dome-shaped mold cap  242  also is raised over the top of the leadframe  22 . The dome-shaped mold cap  242  is suitable to create packages that are thicker, such as one that has a thickness greater than 0.2 mm. The dome-shaped mold cap  242  is also more suitable for packages with optical applications. 
       FIG. 26  is a three-dimensional view of an individual leadframe  22  with a dome-shaped mold cap  242 , in accordance with an embodiment of the present invention. 
       FIG. 27  is a three-dimensional view of an individual leadframe  22  lead cut, in accordance with one embodiment of the present invention. After encapsulation, the leadframe strip  20  is then singulated, causing the individual leadframes  22  to separate physically from each other. One of skill in the art will recognize the appropriate specialized tools to singulate the leadframe strip  20 .  FIG. 27  specifically shows the use of a lead cut punch  262  along each of the sides of the leadframe  22 . 
       FIG. 28  is a three-dimensional view of an individual leadframe  22  singulated, in accordance with another embodiment of the present invention. In this embodiment,  FIG. 28  specifically shows the use of a singulation punch  272  along each of the sides of the leadframe  22 . 
     Singulation of an individual molded package includes 2 steps. Firstly, a singulation punch  262  ( FIG. 27 ) along each of the sides of the leadframe  22  is carried out to separate the leads from the leadframe. Next, a singulation punch  272  ( FIG. 28 ) along each of the corners of the leadframe is carried out to separate the tie bars from the leadframe. 
       FIG. 29  is a top three-dimensional view of a singulated leadframe unit  282 , in accordance with one embodiment of the present invention. 
       FIG. 30  is a bottom three-dimensional view of a singulated leadframe unit  292 , in accordance with one embodiment of the present invention. 
     Although not illustrated, the electronic packages can be configured such that the top side of the electronic package can be mounted onto a printed circuit board (PCB) with the bottom side of the package facing upwards with the exposed metal die paddle facing away from the PCB surface. An additional heatsink can also be attached to the metal die paddle for enhanced heat dissipation. Additionally the electronic packages can be stacked one on top of the other depending on the required application. In this embodiment, instead of stacking two or more chips within one package for additional functionality, two or more packages are staked on top of each other, where each package can have one chip with specific functionality. 
     It will also be recognized by those skilled in the art that, while the invention has been described above in terms of preferred embodiments, it is not limited thereto. Various features and aspects of the above-described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment and for particular applications, those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be utilized in any number of environments and implementations.