Patent Publication Number: US-2023143672-A1

Title: Molded microfluidic substrate having microfluidic channel

Description:
BACKGROUND 
     Microfluidic devices leverage the physical and chemical properties of liquids and gases at a small scale, such as at a sub-millimeter scale. Microfluidic devices geometrically constrain fluids to precisely control and manipulate the fluids for a wide variety of different applications. Such applications can include digital microfluidic (DMF) and DNA applications, as well as applications as varied as lab-on-a-chip, inkjet, electrophoresis, capacitance sensing, fluidic heat sink, and fluidic sensor probe applications, among other applications. A microfluidic device can include a microfluidic substrate in which a series of microfluidic channels are etched or molded. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a flowchart of an example method for making a molded microfluidic substrate having a microfluidic channel corresponding to a sacrificial metal bond wire. 
         FIGS.  2 A,  2 B,  2 C, and  2 D  are cross-sectional diagrams of different example metal bond layers that can be used in the method of  FIG.  1   . 
         FIG.  3    is a diagram illustrating example performance of the method of  FIG.  1    in which uncoated and coated sacrificial metal bond wire and ribbon as well as non-sacrificial metal bond wire and ribbon are attached to a metal bond layer. 
         FIG.  4    is a diagram illustrating example performance of the method of  FIG.  1    in which a molding compound is applied to form a molding compound layer that encapsulates the uncoated and coated sacrificial metal bond wire and ribbon and the non-sacrificial metal bond wire and ribbon, after their attachment in  FIG.  3   . 
         FIG.  5    is a diagram illustrating example performance of the method of  FIG.  1    in which a portion of the formed molding compound layer encapsulating the uncoated and coated sacrificial metal bond wire and ribbon and the non-sacrificial metal bond wire and ribbon is removed, after application of the molding compound in  FIG.  4   . 
         FIGS.  6 A,  6 B, and  6 C  are cross-sectional, top, and bottom diagrams of an example molded microfluidic substrate having a microfluidic channel corresponding to a sacrificial metal bond layer, which can be fabricated by example performance of the method of  FIG.  1    in which the sacrificial metal is etched away, after removal of a portion of the molding compound layer in  FIG.  5   . 
         FIG.  7 A  is a cross-sectional diagram illustrating example masking of a non-sacrificial metal bond wire of the same metal as a sacrificial metal bond wire or ribbon prior to etching.  FIG.  7 B  is a cross-sectional diagram of a portion of an example molded microfluidic substrate after removal of the mask of  FIG.  7 A . 
         FIG.  8    is a block diagram of an example molded microfluidic substrate having a microfluidic channel. 
         FIG.  9    is a diagram of an example electronic device having a molded microfluidic substrate with a microfluidic channel. 
         FIG.  10    is a flowchart of an example method for making a molded microfluidic substrate having a microfluidic channel. 
     
    
    
     DETAILED DESCRIPTION 
     As noted in the background section, a microfluidic device can include a microfluidic substrate in which microfluidic channels are etched or molded. Different processes can be employed to fabricate microfluidic substrates having such channels. The different processes have competing tradeoffs as to, among other things, the types of microfluidic channels that can be formed, as well as the overall cost of substrate fabrication. In general, relatively complex microfluidic substrates having three-dimensional (3D) microfluidic channels are costly to manufacture, making microfluidic devices more expensive and therefore not employed as widely as may be desired. 
     For example, injection-molded cyclic olefin copolymer (COC) microfluidic substrates can be manufactured inexpensively, but are generally limited to formation of two-dimensional (2D) microfluidic channels. Fabricating microfluidic substrates by instead using photolithographic deposition and etching processes permits formation of 3D microfluidic channels, but such processes are much more expensive. Fabricating microfluidic substrates by molded interconnect substrate (MIS) processes also permits formation of 3D channels, and while such processes are less expensive than pure photolithographic techniques, they are still relatively expensive. 
     Techniques described herein provide for a molded microfluidic substrate having a microfluidic channel corresponding to an etched-away sacrificial bond wire or ribbon. A sacrificial bond wire can be attached to a metal bond wire, and then bent in correspondence with a desired microfluidic channel to be formed. Molding compound can be applied to encase the sacrificial metal bond wire within a molding compound layer. After removal of a portion of the molding compound layer, the resultantly exposed sacrificial metal bond wire is etched away, yielding the microfluidic substrate having the desired microfluidic channel formed within the molding compound layer. 
     This novel molding process is much less expensive than the 3D-oriented approaches outlined above. Rather than depositing and etching sacrificial metal in layers using semiconductor-like photolithographic techniques, or forming sacrificial metal in layers using such photolithographic techniques followed by molding compound application as in MIS processes, the described molding process novelly leverages wire bonding processes normally used for integrated circuit (IC) packaging. Such wire bonding processes permit more cost effective 3D microfluidic channel definition. Once the sacrificial metal bond wires have been attached, they are encased in molding compound and ultimately etched away to innovatively yield a microfluidic substrate. 
     Furthermore, the described techniques can simply and cost effectively provide for molded microfluidic substrates having metal-plated or metal-coated microfluidic channels. Many metal bond wires used in IC packaging are coated with metal, such as palladium-coated copper (PCC) and silver (PCS) bond wires. The core metal can be selectively etched away, leaving the non-etched metal coating to encase the now-hollow cores within the molding compound layer, and thus realizing a microfluidic substrate having metal-coated microfluidic channels without having to perform any additional fabrication steps or acts, and so on. Instead, a coated as opposed to uncoated metal bond wire is attached, and the subsequent metal etching is selective to the core metal of the bond wire. 
       FIG.  1    shows an example method  100  for making a molded microfluidic substrate. The method  100  includes providing a metal bond layer ( 102 ). Providing the metal bond layer can include forming an MIS sacrificial metal bond layer having a sacrificial metal portion. Such an MIS sacrificial metal bond layer is formed using MIS techniques, in which sacrificial metal is selectively deposited via photolithographic processes and then molding compound is applied. The sacrificial metal may be copper, gold, aluminum, silver, or another type of metal. The molding compound may be epoxy molding compound (EMC). 
     Providing the metal bond layer can instead include providing a non-MIS sacrificial metal carrier, such as a copper, gold, aluminum, silver, or other type of metal carrier. Providing the metal bond layer can instead include providing a semiconductor die having non-sacrificial metal bond pads that act as the metal bond layer. Providing the metal bond layer can instead include providing a semiconductor package in which a semiconductor die has been disposed, and which has non-sacrificial metal contact pads that act as the metal bond layer. The metal bond layer may be provided in a different manner as well. 
       FIGS.  2 A,  2 B,  2 C, and  2 D  show cross sections of different examples of a metal bond layer  200 . In  FIG.  2 A , the metal bond layer  200  is an MIS sacrificial metal bond layer having molding compound  202  planarly surrounding sacrificial metal portions  204 A,  204 B,  204 C,  204 D, and  204 E, which will be subsequently etched away, and which are collectively referred to as the sacrificial metal portions  204 . Uncoated and coated sacrificial and non-sacrificial metal bond wire and ribbon can be subsequently attached to the sacrificial metal portions  204 . The sacrificial metal portions  204  correspond to desired portions of microfluidic channels to be formed within the molded microfluidic substrate under manufacture. 
     In  FIG.  2 B , the metal bond layer  200  includes a non-MIS sacrificial metal carrier  212  that will be subsequently etched away and to which uncoated and coated sacrificial and non-sacrificial metal bond wire and ribbon can be subsequently attached. In  FIG.  2 C , a semiconductor die  222  has non-sacrificial metal bond pads  224  that act as the metal bond layer  200 . In  FIG.  2 D , a semiconductor package  232  has non-sacrificial metal contact pads  234  that act as the metal bond layer  200 . Uncoated and coated sacrificial and non-sacrificial metal bond wire and ribbon can be subsequently attached to the bond pads  224  and contact pads  234  of  FIGS.  2 C and  2 D , respectively. 
     Referring back to  FIG.  1   , the method  100  includes attaching a sacrificial metal bond wire to the provided metal bond layer ( 104 ). The method  100  further includes bending the sacrificial metal bond wire in correspondence with a desired microfluidic channel to be formed within the molded microfluidic substrate under manufacture ( 106 ). The sacrificial metal bond wire may be uncoated sacrificial metal bond wire, such as uncoated copper, gold, aluminum, silver, or other uncoated metal bond wire. 
     The sacrificial metal bond wire may be a coated sacrificial metal bond wire, in which a sacrificial metal core is surrounded by an outer non-sacrificial metal surface. The sacrificial metal core may be copper, gold, aluminum, silver, or another metal. The non-sacrificial metal outer-metal coated surface may be palladium, silver (if the sacrificial metal core is not silver), or another metal that is different than the sacrificial metal core. 
     Attachment and subsequent bending of the sacrificial metal bond wire can be performed using metal wire bonding processes that are normally used for IC packaging. Such wire bonding processes are normally used to make interconnections between an IC or other semiconductor device and its packaging during semiconductor device fabrication. Such processes are also less commonly used to connect an IC to other electronics or to connect from one printed circuit board (PCB) to another. 
     The method  100  can include attaching a sacrificial metal ribbon to the metal bond layer ( 108 ), and may include bending the sacrificial metal ribbon ( 109 ). The sacrificial metal ribbon, as may be bent, corresponding to a desired microfluidic channel to be formed within the molded microfluidic substrate under manufacture. The sacrificial metal ribbon can be of the same sacrificial metal as the attached sacrificial metal bond wire. Whereas the sacrificial metal bond wire is generally round in cross-sectional shape, the sacrificial metal ribbon is generally rectangularly flat in cross-sectional shape. 
     The method  100  can include attaching a non-sacrificial metal bond wire to the metal bond layer ( 110 ). The method  100  can include bending the non-sacrificial metal bond wire in correspondence with a desired metal component to be formed within the microfluidic substrate under manufacture ( 112 ). The method  100  can include attaching a non-sacrificial metal ribbon ( 114 ), and may include bending the non-sacrificial metal ribbon ( 115 ). The non-sacrificial metal ribbon, as may be bent, corresponds to a desired metal component to be formed within the substrate under manufacture. 
     The non-sacrificial metal bond wire and ribbon may be palladium, silver (if the sacrificial metal bond wire is not silver), or another metal that is different than the sacrificial metal bond wire. The metal component to be formed by the non-sacrificial metal bond wire may be a conductive interconnect or other type of metal component. The metal component to be formed by the non-sacrificial metal ribbon may be a heat sink, conductive or capacitive plate, or other type of metal component. 
       FIG.  3    shows example performance of parts  104 ,  106 ,  108 ,  110 ,  112 , and  114  of the method  100  after part  102  has already been performed. In the example of  FIG.  3   , the metal bond layer  200  is the MIS sacrificial metal bond layer of  FIG.  2 A , which includes molding compound  202  planarly surrounding sacrificial metal portions  204 .  FIG.  3    shows sacrificial metal bond wires  302 A,  302 B, and  302 C, collectively referred to as the sacrificial metal bond wires  302 ; a sacrificial metal ribbon  303 ; non-sacrificial metal bond wires  306 A and  306 B, collectively referred to as the non-sacrificial metal bond wires  306 ; and a non-sacrificial metal ribbon  308 . 
     The sacrificial metal bond wire  302 A is uncoated, and can be of the same sacrificial metal as the sacrificial metal portions  204  of the metal bond layer  200 . One end of the sacrificial metal bond wire  302 A is attached to the sacrificial metal portion  204 A. The bond wire  302 A is then bent in correspondence with a desired microfluidic channel to be formed within the microfluidic substrate under manufacture. 
     The sacrificial metal bond wire  302 B is coated with a non-sacrificial metal coating  304 . The core metal of the bond wire  302 B can be of the same sacrificial metal as the sacrificial metal portions  204  of the metal bond layer  200 , whereas the non-sacrificial metal coating  304  is of a different metal. One end of the bond wire  302 B is attached to the sacrificial metal portion  204 A and bent in correspondence with a desired microfluidic channel to be formed within the microfluidic substrate under manufacture, prior to attachment of the other end of the wire  302 B to the sacrificial metal portion  204 B. 
     The sacrificial metal bond wire  302 C is uncoated, and can be of the same sacrificial metal as the sacrificial metal portions  204  of the metal bond layer  200 . One end of the bond wire  302 C is attached to the sacrificial metal portion  204 E, and is bent in correspondence with a desired microfluidic channel to be formed within the microfluidic substrate under manufacture. The other end of the bond wire  302 B is then attached to the same sacrificial metal portion  204 E. 
     The sacrificial metal ribbon  303  is uncoated, and can be of the same sacrificial metal as the sacrificial metal portions  204  of the metal bond layer  200 . One end of the ribbon  303  is attached the sacrificial metal portion  204 D, and is bent in correspondence with a desired microfluidic channel to be formed within the microfluidic substrate under manufacture. The other end of the ribbon  303  is then attached to the sacrificial metal portion  204 E. 
     The non-sacrificial metal bond wire  306 A is uncoated, and is of a different metal than the sacrificial metal portions  204  of the metal bond layer  200 . The bond wire  306 A may be of the same metal as the non-sacrificial metal coating  304  of the sacrificial metal bond wire  302 B. One end of the bond wire  306 A is attached to the sacrificial metal portion  204 C, and is then bent in correspondence with a desired metal component to be formed within the microfluidic substrate under manufacture. 
     The non-sacrificial metal bond wire  306 B is also uncoated, and is of a different metal than the sacrificial metal portions  204  of the metal bond layer  200 . The bond wire  306 B may be of the same metal as the non-sacrificial metal coating  304  of the sacrificial metal bond wire  302 B, and/or of the same metal as the non-sacrificial metal bond wire  306 A. One end of the bond wire  306 B is attached to the sacrificial metal portion  204 D, and is bent in correspondence with a desired metal component to be formed within the microfluidic substrate under manufacture, prior to attachment of the other end of the bond wire  306 B to the same sacrificial metal portion  204 D. 
     The non-sacrificial metal ribbon  308  is uncoated, and is of a different metal than the sacrificial metal portions  204  of the metal bond layer  200 . The ribbon  308  may be of the same metal as the non-sacrificial metal coating  304  of the sacrificial metal bond wire  302 B, and/or of the same metal as the non-sacrificial metal bond wires  306 . The ribbon  308  is attached to the sacrificial metal bond wire  302 C that is bent and attached to the sacrificial metal portion  204 E. The ribbon  308  corresponds to a desired metal component to be formed within the microfluidic substrate under manufacture. 
       FIG.  3    thus shows where and which ends of the bond wires  302  and  306  and the ribbons  303  and  308  are each attached can vary. As to the sacrificial metal bond wire  302  and ribbon  303 , such variation in attachment, as well as variation in bending, is governed by the microfluidic channels that are desired to be formed within the molded microfluidic substrate under manufacture. As to the non-sacrificial metal bond wire  306  and ribbon  308 , such variation in attachment, as well as variation in bending, is governed by the metal components that are desired to be formed within the microfluidic substrate under manufacture. 
     Referring back to  FIG.  1   , the method  100  includes applying molding compound ( 116 ), such as EMC. Application of molding compound encapsulates the sacrificial metal bond wire and ribbon and the non-sacrificial bond wire and ribbon within a molding compound layer, such that there are no air gaps within the layer. The molding compound can be applied in a manner similar to its application in an MIS process, with a difference being that the molding compound is applied around bond wire and ribbon in a single application or layer, as opposed to around photolithographically defined metal in multiple applications as such metal layers are formed. 
       FIG.  4    shows example performance of part  116  of the method  100  after parts  104 ,  106 ,  108 ,  110 ,  112 , and  114  have already been performed. The example of  FIG.  4    includes the sacrificial metal bond wires  302  and ribbon  303  and the non-sacrificial metal bond wires  306  and ribbon  308  of  FIG.  3   . The same molding compound  202  of the metal bond layer  200  that also includes the sacrificial metal portions  204  is applied, encapsulating the bond wires  302  and  306  and the ribbons  303  and  308  within a molding compound layer  400 . In the example of  FIG.  4   , none of the bond wires  302  and  306  and the ribbons  303  and  308  are exposed within the molding compound layer  400 . 
     Referring back to  FIG.  1   , the method  100  includes removing a portion of the molding compound layer ( 118 ). Removal of a portion of the molding compound layer exposes some or all of the sacrificial metal bond wires and ribbons and the non-sacrificial metal bond wires and ribbons within the layer. The portion of the molding compound layer can be removed by shaving or grinding, among other molding compound layer portion removal techniques. 
       FIG.  5    shows example performance of part  118  of the method  100  after part  116  has already been performed. The example of  FIG.  5    includes the sacrificial metal bond wires  302  and ribbon  303  and the non-sacrificial metal bond wires  306  and ribbon  308  encapsulated within the molding compound layer  400  of molding compound  202  atop the metal bond layer  200  that also includes molding compound  202  as well as the sacrificial metal portions  204 . A top portion of the molding compound layer  400  is removed in  FIG.  5   , exposing a majority of the bond wires  302  and  306  and the ribbons  303  and  308 . 
     The heights of the sacrificial metal bond wire  302 A and the non-sacrificial metal bond wire  306 A are reduced after removal of a portion of the molding compound layer  400 . The coated sacrificial metal bond wire  302 B has been divided into separate coated sacrificial metal bond wires  302 B′ and  3026 ″; likewise, the non-sacrificial metal bond wire  306 B has been divided into separate non-sacrificial metal bond wires  306 B′ and  306 B″. The horizontal top portions of the sacrificial metal ribbon  303  and the non-sacrificial ribbon  308  have been reduced in height. The sacrificial metal bond wire  302 C remains encapsulated and not exposed within the molding compound layer  400 , however. 
     Referring back to  FIG.  1   , the method  100  includes etching away the sacrificial metal bond wire ( 120 ). Any other sacrificial metal is likewise etched away, such as the sacrificial metal ribbon and any sacrificial metal of the metal bond layer on which the bond wire and ribbon have been attached. The etching is selective to the sacrificial metal. The non-sacrificial metal coating of any coated sacrificial bond wire remains, as does any non-sacrificial metal bond wire and ribbon. Etching away the sacrificial metal yields a molded microfluidic substrate having microfluidic channels formed within the molding compound layer and which correspond to the etched-away metal bond wire and ribbon. 
       FIGS.  6 A,  6 B, and  6 C  respectively show cross-sectional, top, and bottom views of a molded microfluidic substrate  600  that performance of part  120  of the method  100  yields after part  118  has already been performed. The example of  FIGS.  6 A,  6 B, and  6 C  includes microfluidic channel portions  602 A,  602 B,  602 C,  602 D,  602 E,  602 F,  602 G,  602 H,  602 I, and  602 J, which are collectively referred to as the microfluidic channel portions  602 , within the molding compound layer  601  of molding compound  202 . The example includes metal components corresponding to the non-sacrificial metal bond wires  306  and ribbon  308  within the molding compound layer  601 . 
     The molding compound layer  601  encompasses the molding compound  202  of the metal bond layer  200  of  FIG.  5    and the molding compound layer  400  of  FIG.  5    in height. A microfluidic channel corresponding to the etched-away sacrificial metal bond wire  302 A of  FIG.  5    includes the microfluidic channel portion  602 A remaining after the bond wire  302 A has been etched away and the microfluidic channel portion  602 B remaining after the sacrificial metal portion  204 A of  FIG.  5    has been etched away. The portion  204 A has a round sidewall corresponding to the round profile of the etched-away bond wire  302 A. The portion  602 B is at the bottom exterior surface of the molding compound layer  601  and corresponds to the etched-away sacrificial metal portion  204 A. 
     A microfluidic channel corresponding to the etched-away sacrificial metal bond wire  302 B′ of  FIG.  5    includes the microfluidic channel portion  602 C remaining after the bond wire  302 B′ has been etched away and the microfluidic channel portion  602 B. The microfluidic channel portion  602 C has a metal-plated sidewall corresponding to the non-sacrificial metal coating  304  that remains after the inner sacrificial metal core of the metal bond wire  302 B′ has been etched away. The microfluidic channel portion  602 C has a round sidewall corresponding to the round profile of the bond wire  302 B′. 
     A microfluidic channel corresponding to the etched-away sacrificial metal bond wire  302 B″ of  FIG.  5    includes the microfluidic channel portion  602 D remaining after the bond wire  302 B″ has been etched away and the microfluidic channel portion  602 E remaining after the sacrificial metal portion  204 B of  FIG.  5    has been etched away. The portion  602 D has a metal-plated sidewall corresponding to the non-sacrificial metal coating  304  that remains after the inner sacrificial metal core of the metal bond wire  302 B″ has been etched away. The portion  602 D has a round sidewall corresponding to the round profile of the bond wire  302 B″. The portion  602 E is at the bottom exterior surface of the molding compound layer  601  and corresponds to the etched-away sacrificial metal portion  204 B. 
     A microfluidic channel corresponding to the etched away sacrificial metal ribbon  303  of  FIG.  5    includes the microfluidic channel portion  602 F remaining after the ribbon  303  has been etched away, and the microfluidic channel portions  602 G and  602 H remaining after the sacrificial metal portions  204 D and  204 E of  FIG.  5    have respectively been etched away. The microfluidic channel portions  602 H and  602 H are at the bottom exterior surface of the molding compound layer  601 . The portions  602 G and  602 H respectively correspond to the etched-away sacrificial metal portions  204 D and  204 E. 
     A microfluidic channel corresponding to the etched-away sacrificial metal bond wire  302 C of  FIG.  5    includes the microfluidic channel portion  602 I remaining after the bond wire  302 C has been etched away and the microfluidic channel portion  602 H remaining after the sacrificial metal portion  204 E has respectively been etched away. Microfluidic channels within the molding compound layer  601  of the microfluidic substrate  600  thus correspond to the etched-away sacrificial metal bond wire  302  and ribbon  303 . Each microfluidic channel includes multiple microfluidic channel portions  602  in the example of  FIGS.  6 A,  6 B, and  6 C . More generally, each microfluidic channel can include as few as one microfluidic channel portion  602 . 
     A metal component of the molded microfluidic substrate  600  corresponds to and is formed by the non-sacrificial metal bond wire  306 A that remains after etching and that is exposed at the microfluidic channel portion  602 J. The microfluidic channel portion  602 J remains after the sacrificial metal portion  204 C of  FIG.  5    has been etched away. The microfluidic channel portion  602 J thus corresponds to the etched-away sacrificial metal portion  204 C. 
     A metal component of the molded microfluidic substrate  600  corresponds to and is formed by the non-sacrificial metal bond wire  306 B′ that remains after etching and that is exposed at the microfluidic channel portion  602 G. A metal component corresponds to and is formed by the non-sacrificial metal bond wire  306 B″ and that is also exposed at the portion  602 G. Similarly, a metal component corresponds to and is formed by the non-sacrificial metal ribbon  308  that remains after etching and that is exposed at the microfluidic channel portion  602 I. 
     In the examples that have been described, the non-sacrificial metal bond wire and ribbon are a different metal than the sacrificial metal bond wire and ribbon. However, in another implementation, the non-sacrificial metal bond wire and/or ribbon may be the same metal as the sacrificial metal bond wire and/or ribbon. In such instance, the non-sacrificial metal bond wire and/or ribbon in question is masked prior to etching away the sacrificial metal bond wire and ribbon so that the non-sacrificial metal bond wire and/or ribbon is not also etched away. The mask is removed after etching. 
       FIGS.  7 A and  7 B  show an example of such an implementation in which the non-sacrificial metal bond wire and/or ribbon is of the same metal as the sacrificial metal bond wire and/or ribbon.  FIG.  7 A  shows a masking layer  702 A applied above the molding compound layer  400  to cover the non-sacrificial metal bond wire  306 A′.  FIG.  7 A  similarly shows a masking layer  702 B applied below the metal bond layer  200  to cover the metal portion  204 C. 
     The masking layers  702  can be applied after part  118  of the method  100  of  FIG.  1    is performed, as shown in  FIG.  5   . Just a portion of the molding compound layer  400  and the metal bond layer  200  of  FIG.  5    are shown in  FIG.  7 A . Furthermore,  FIG.  7 A  differs from  FIG.  5    in that  FIG.  7    includes a non-sacrificial metal bond wire  306 A′ of the same metal as the sacrificial metal bond wires  302 , ribbon  303 , and portions  204  of  FIG.  5   . By comparison,  FIG.  5    includes a non-sacrificial metal bond wire  306 A of a different metal than the sacrificial metal bond wires  302 , ribbon  303 , and portions  204 . 
       FIG.  7 B  shows an example of the molded microfluidic substrate  600  that performance of part  120  of the method  100  of  FIG.  1    yields after part  118  is performed and the masking layers  702  of  FIG.  7 A  is then subsequently removed. The microfluidic substrate  600  of  FIG.  7 B  is similar but not identical to the substrate  600  of  FIG.  6   . Just a portion of the substrate  600  of  FIG.  6    is shown in  FIG.  7 B . 
     Specifically,  FIG.  7 B  shows a metal component within the molding compound layer  601  which corresponds to and is formed by the non-sacrificial metal bond wire  306 A′ and metal portion  204 C. The bond wire  306 A′ and metal portion  204 C are not removed during etching due to their being masked by the masking layers  702  of  FIG.  7 A . By comparison,  FIG.  6    shows a metal component corresponding to and formed by the non-sacrificial metal bond wire  306 A, which is not removed during etching due to its being a different metal than the sacrificial metal bond wires  302 , ribbon  303 , and portions  204  of  FIG.  5   . 
       FIG.  8    shows a block diagram of the example molded microfluidic substrate  600 . The molded microfluidic substrate  600  includes the molding compound layer  601  and a microfluidic channel  802  formed within the molding compound layer  601  and corresponding to a sacrificial metal bond wire. For example, the microfluidic channel  802  can correspond to any of the sacrificial metal bond wires  302  of  FIGS.  3 - 5    that are etched away. The substrate  600  is a molded substrate in that it is formed via application of molding compound  202  to encapsulate the sacrificial metal bond wires  302  within the molding compound layer  400  in  FIG.  4   . The substrate  600  can be a 3D substrate in that, for instance, the sacrificial metal bond wire to which the channel  802  corresponds can be bent in all three spatial dimensions as desired. 
       FIG.  9    shows a block diagram of an electronic device  900 , such as a microfluidic electronic device. The electronic device  900  includes the molded microfluidic substrate  600 , which itself can include the microfluidic channel  802  and a metal component  904 . The microfluidic channel  802  corresponds to a sacrificial metal bond wire or ribbon, such as any of the sacrificial metal bond wires  302  and ribbon  303  of  FIGS.  3 - 5    that are etched away. The metal component  904  corresponds to a non-sacrificial metal bond wire or ribbon, such as any of the non-sacrificial metal bond wires  306  and ribbon  308  of  FIGS.  3 - 5  and  7 A- 7 B  that are not etched away. 
     The electronic device  900  further includes an IC  902 . The IC  902  may be in conductive contact with the metal component  904 , in fluidic contact with the microfluidic channel  802 , or in both conductive contact with the metal component  904  and fluidic contact with the microfluidic channel  802 . The electronic device  900  can thus provide for electronic functionality to be performed by the IC  902  in relation to fluid routed through the molded microfluidic substrate  600 . The electronic device  900  can in another implementation provide for active or passive cooling of the IC  902  via fluid routed through the molded microfluidic substrate  600 . 
       FIG.  10    shows an example method  1000  for making a molded microfluidic substrate having a microfluidic channel. The method  1000  is consistent with but more general than the method  100  of  FIG.  1    that has been described. The method  1000  includes providing a metal bond layer ( 102 ), and attaching a sacrificial metal bond wire to the metal bond layer ( 104 ). The method  1000  includes bending the sacrificial metal bond wire in correspondence with a microfluidic channel to be formed ( 106 ). 
     The method  1000  includes applying a molding compound ( 114 ) to encase the sacrificial metal bond wire within a molding compound layer. The method  1000  includes then removing a portion of the molding compound layer ( 116 ) to expose the sacrificial metal bond wire within the molding compound layer. The method  1000  includes etching away the sacrificial metal bond wire ( 118 ) to yield a molded microfluidic substrate having the microfluidic channel formed within the molding compound layer and corresponding to the etched-away sacrificial metal bond wire. 
     Techniques have been described for making a molded microfluidic substrate having a microfluidic channel corresponding to a sacrificial bond wire. Such a molded microfluidic substrate can be less expensive to manufacture using the techniques described herein than 3D microfluidic substrates formed by other processes. The sidewall microfluidic channel can be coated with metal without the addition of further fabrication steps or acts, and so on.