Patent Description:
An inductor or coil is a passive two-terminal device that stores energy in a magnetic field in response to current passing through the inductor. DC-DC converters are electronic devices that use coils to convert an input direct current (DC) voltage into one or more DC output voltages. The DC output voltage(s) may be higher (boost or step-up converter) or lower (buck or step-down converter) than the DC input voltage.

Some DC-DC converters may include a switch for alternately opening and closing a current path through an inductor in response to a switching signal. In operation, a DC voltage is applied across the inductor. Electrical energy is transferred to a load connected to the inductor by alternately opening and closing the switch as a function of the switching signal. The amount of electrical energy transferred to the load is a function of the duty cycle of the switch and the frequency of the switching signal. DC-DC converters are used in electronic portable devices, particularly battery-powered devices, such as portable cellular phones, laptop computers, and other electronic systems in which efficient use of power is desirable. In the European Search Report the following documents have been cited: <CIT> relating to a semiconductor package with an integrated passive electrical component; <CIT> disclosing methods and an apparatus related to a package including a semiconductor die.

In described examples, a method of fabricating integrated circuits includes providing a substrate having an array of electronic components and attaching a sheet array of substrate-based coils to the substrate where respective substrate-based coils are aligned with respective electronic components. The substrate having the array of electronic components and the sheet of substrate-based coils are encapsulated with a magnetic mold compound after soldering of the substrate-based coils. The array of electronic components and respective substrate-based coils are singulated to form the integrated circuits.

In another described example, an integrated circuit includes a substrate having an electronic component. A substrate-based coil is on the substrate and the electronic component and is electrically coupled to the electronic component. A one-piece magnetic mold compound encapsulates the substrate-based coil and the electronic component.

To fabricate smaller integrated circuit die, reducing the profile of integrated circuits (IC) that use coils (inductors), such as DC-DC converter modules, and integrating the coils into a package with the die is important to creating a low-profile power modules. Described herein are substrate-based coils and a method to make thereof for use in an IC, such as in DC-DC converter modules, transformers, etc. The substrate-based coils and the die are integrated into the same package and molded with a magnetic mold compound (MMC) to achieve the low-profile IC. The substrate-based coils are copper (Cu)-plated coils that are applied to a dielectric by methods, such as printing, etching and depositing, plating, etc. to create a sheet of coils. The process of fabricating the coils creates a very narrow gap between the coils, which leads to a higher inductance.

In the fabrication method described herein for the example IC, the IC is fabricated in an array that includes a number of ICs. Each IC of the array includes a substrate (leadframe) on which electronic components are mounted or embedded. A die comprising semiconductors and passive components (other than magnetics) is affixed to or embedded in the substrate. Thereafter the sheet of coils is disposed atop the die and affixed to the substrate. The entire array of electronic components, including the coils and the die, is encapsulated in the MMC after attachment of the sheets of coils to the substrate. After encapsulation, the ICs are singulated. Implementations of this description allow for a low-profile IC due to the fabrication of the substrate-based coils and by encapsulating the entire IC in the MMC.

<FIG> are perspective and front views of a low-profile IC (e.g., DC-DC converter module) <NUM> that includes substrate-based coils (inductors) in accordance with various examples. The IC <NUM> includes a substrate (leadframe) <NUM> and electronic components <NUM> attached to a surface of the substrate <NUM>. The substrate <NUM> is an interconnect board interconnected to the electronic components <NUM> and includes first and second substrate contacts <NUM>, <NUM> disposed on the surface of the substrate <NUM>. The electronic components <NUM> may include one or more power supply switching components (e.g., a power supply controller and/or discrete transistors) or various other electronic components (e.g., resistors, capacitors, etc.).

The IC <NUM> further includes a substrate-based coil comprising a first coil portion <NUM>, a second coil portion <NUM>, and coil interconnects <NUM>, via copper (Cu) plating, (see <FIG>) disposed in adjoining dielectric layers (e.g., FR4, Teflon, etc.) <NUM>. A first end <NUM> of the first coil portion <NUM> terminates proximate an outer periphery <NUM> of the dielectric layer <NUM> and is connected to the first substrate contact <NUM> via a first substrate interconnect (e.g., solder ball) <NUM>. A second end <NUM> of the first coil portion <NUM> terminates proximate a center <NUM> of the dielectric layer <NUM>. A first end <NUM> of the second coil portion <NUM> terminates proximate the outer periphery <NUM> of the dielectric layer <NUM> at an opposite side than that of the termination of the first end <NUM> of the first coil portion <NUM>. The first end <NUM> of the second coil portion <NUM> is connected to the second substrate contact <NUM> via a second substrate interconnect <NUM>. A second end <NUM> of the second coil portion <NUM> terminates proximate the center <NUM> of the dielectric layer <NUM>.

A magnetic mold compound (MMC) <NUM> encapsulates the electronic components <NUM>, the first and second coil portions <NUM>, <NUM>, and the dielectric layer <NUM> to form the IC <NUM>. The MMC <NUM> applied to encapsulate the IC <NUM> may include ferromagnetic material, such as ferrite that enhances the operation of (e.g., increases the inductance of) the first and second coil portions <NUM>, <NUM>. The MMC <NUM> also provides shielding from electromagnetic interference, and protects the electronic components of the IC <NUM> from the environment.

In block <NUM>, an array of electronic components <NUM> are attached to a substrate <NUM> to form an array of electronic component modules <NUM>. The substrate <NUM> may be one-dimensional or two-dimensional. For example, module substrates may be formed on a sheet of substrate material, such as printed circuit board material. In some implementations, a module substrate may include a lead frame, have laminate material, have ceramic material, or other metal/dielectric arrangement that provides conductive connections for electronic components of the switch-mode converter and terminals for connection of the switch-mode converter module to an external device or circuit.

Electronic components, such as a die, semiconductors, resistors, and/or capacitors are attached to the substrate of each IC being fabricated. For example, if an 8x8 array of ICs is being fabricated, then one or more dies (e.g., power supply controller integrated circuits, or switching transistors) and associated resistors, capacitors, etc. may be attached to each of the <NUM> module substrates of the 8x8 array. The components may be affixed to the substrate by solder paste, conductive adhesive, or other adhesive substance suitable for attaching electronic components to a substrate. Alternatively, the electronic components can be embedded in the substrate.

In block <NUM>, substrate interconnects (e.g., solder balls, bump bonds, etc.) <NUM> are disposed on substrate contacts that are disposed on a surface of the substrate. The substrate interconnects <NUM> may be disposed by methods, such as evaporated solder bumping, electroplated solder bumping, printed solder bump formation, or solder ball bumping.

In block <NUM>, a sheet array <NUM> of coils <NUM> is placed on the substrate interconnects <NUM>. The sheet array <NUM> of coils <NUM> are aligned on the substrate <NUM> such that respective substrate-based coils <NUM> are aligned with respective electronic components <NUM> from the array of electronic components <NUM>. The sheet array <NUM> of coils <NUM> are substrate-based coils that may be fabricated by methods, such as printing, etching and depositing, plating, etc..

For example, <FIG> is a flow diagram <NUM> of one example process to fabricate the sheet of substrate-based coils <NUM> in a dielectric layer <NUM> illustrated in <FIG>. The process begins in block <NUM> with a first dielectric layer (e.g., FR4, Teflon, etc.). In block <NUM>, vias are laser drilled into a first dielectric layer. In block <NUM>, a seed layer of an electrically conductive material (e.g., copper) is deposited on the first dielectric layer. In block <NUM>, the first dielectric layer is laminated with a thin layer of photoresist. In block <NUM>, the coil pattern is digitally formed onto the first dielectric layer by a laser (e.g., laser direct imaging). In block <NUM>, a developer is applied to the first dielectric layer to remove the photoresist layer in places that are not protected by a mask. In block <NUM>, the electrically conductive material is deposited on the surface of the dielectric layer in the coil pattern formed by the laser. In block <NUM>, the remaining photoresist layer is stripped away via a chemical process. In block <NUM>, wire traces are routed on the dielectric layer to make electrical connections to external components. In block <NUM>, a desmear process is performed to remove any resin from the vias. In block <NUM>, a dielectric coating is applied to the dielectric layer. The process forms a first coil portion <NUM> in a first dielectric layer.

The process is repeated in a similar fashion to create coil interconnects <NUM>, via CU-plating, in a second dielectric layer that overlays the first dielectric layer. Finally, the process is repeated to form a second coil portion <NUM> in a third dielectric layer that overlays the second dielectric layer. The formation of the first, second, and third dielectric layers form the dielectric layer <NUM> illustrated in <FIG>.

The first and second coil portions <NUM>, <NUM> are stacked adjacent to one another (see <FIG>) such that a surface <NUM> of the first coil portion <NUM> faces a surface <NUM> of the second coil portion <NUM>. The first and second coil portions <NUM>, <NUM> are separated by a narrow gap <NUM>. The narrow gap <NUM> between the first and second coil portions <NUM>, <NUM> creates a low-profile IC having a higher inductance. A first end <NUM> of the first coil portion <NUM> terminates proximate an outer periphery <NUM> of the dielectric layer <NUM> and is connected a respective substrate interconnect. A second end <NUM> of the first coil portion <NUM> terminates proximate a center <NUM> of the dielectric layer <NUM>. Similarly, a first end <NUM> of the second coil portion <NUM> terminates proximate the outer periphery <NUM> of the dielectric layer <NUM> at an opposite side than that of the termination of the first end <NUM> of the first coil <NUM>. The first end <NUM> of the second coil portion <NUM> is connected a respective substrate interconnect. A second end <NUM> of the second coil portion <NUM> terminates proximate the center <NUM> of the dielectric layer <NUM>.

Referring back to <FIG> and <FIG>, in block <NUM>, the array of electronic components <NUM> and the sheet array <NUM> of coils <NUM> are bonded to the substrate <NUM>. More specifically, a reflow process is performed to apply solder and heat to the substrate interconnects to mechanically and electrically attach the array of electronic components <NUM> and the sheet array <NUM> of coils <NUM> to the substrate <NUM>. The heat may be supplied by a heat source, such as a reflow oven or an infrared lamp.

In block <NUM>, the array of electronic components <NUM> and the sheet array <NUM> of coils <NUM> are overmolded with the MMC <NUM>. The MMC <NUM> applied to encapsulate the array of electronic components <NUM> and the sheet array <NUM> of coils <NUM> may include ferromagnetic material, such as ferrite that enhances the operation of (e.g., increases the inductance of) the coils <NUM>. The MMC <NUM> also provides shielding from electromagnetic interference, and protects the electronic components of the IC <NUM> from the environment.

In block <NUM>, the array of electronic components <NUM> and respective substrate-based coils are singulated to form the IC <NUM>. The singulation may include dicing, sawing, cutting with a laser, etc. the molded array along row and column boundaries that separate the individual ICs. For example, the singulation may include cutting through the MMC <NUM> and the substrate <NUM> to separate one IC <NUM> from another.

<FIG> are perspective and front views of another example of a low-profile IC (e.g., DC-DC converter module) <NUM> that includes substrate-based coils in accordance with various examples. The IC <NUM> is similar to the IC <NUM> described above, except with different type of substrate interconnects that connect the coils to the substrate.

The IC <NUM> includes a substrate (leadframe) <NUM> and electronic components <NUM> attached to a surface of the substrate <NUM>. The substrate <NUM> functions as an interconnect board interconnected to the electronic components <NUM> and includes first and second substrate contacts <NUM>, <NUM> disposed on the surface of the substrate <NUM>. The electronic components <NUM> may include one or more power supply switching components (e.g., a power supply controller and/or discrete transistors) or various other components (e.g., resistors, capacitors, etc.).

The IC <NUM> further includes a first coil portion <NUM>, a second coil portion <NUM>, and coil interconnects <NUM>, via Cu-plating, disposed in adjoining dielectric layers (e.g., FR4, Teflon, etc.) <NUM>. A first end <NUM> of the first coil portion <NUM> terminates proximate an outer periphery <NUM> of the dielectric layer <NUM> and is connected to the first substrate contact <NUM> via a first pillar interconnect <NUM>. A second end <NUM> of the first coil portion <NUM> terminates proximate a center <NUM> of the dielectric layer <NUM>. A first end <NUM> of the second coil portion <NUM> terminates proximate the outer periphery <NUM> of the dielectric layer <NUM> at an opposite side than that of the termination of the first end <NUM> of the first coil portion <NUM>. The first end <NUM> of the second coil portion <NUM> is connected to the second substrate contact <NUM> via a second pillar interconnect <NUM>. A second end <NUM> of the second coil portion <NUM> terminates proximate the center <NUM> of the dielectric layer <NUM>.

A magnetic mold compound (MMC) <NUM> encapsulates the electronic components <NUM>, the first and second coil portions <NUM>, <NUM>, and dielectric layer <NUM> to form the IC <NUM>. The MMC <NUM> applied to encapsulate the IC <NUM> may include ferromagnetic material, such as ferrite that enhances the operation of (e.g., increases the inductance of) the first and second coil portions <NUM>, <NUM>. The MMC <NUM> also provides shielding from electromagnetic interference, and protects the electronic components of the IC <NUM> from the environment.

<FIG> and <FIG> illustrate a flow diagram <NUM> and a flow process <NUM> respectively for fabricating ICs in accordance with various examples. Though depicted sequentially as a matter of convenience, at least some of the actions shown can be performed in a different order and/or performed in parallel. Alternatively, some implementations may perform only some of the actions shown.

In block <NUM>, an array of electronic components <NUM> are attached to a substrate <NUM> to form an array of electronic component modules <NUM>. The substrate <NUM> may be one-dimensional or two-dimensional. For example, module substrates may be formed on a sheet of substrate material, such as printed circuit board material. In some implementations, a module substrate may include a lead frame, laminate material, ceramic material, or other metal/dielectric arrangement that provides conductive connections for electronic components of the switch-mode converter and terminals for connection of the switch-mode converter module to an external device or circuit.

A die, semiconductors, resistors, and/or capacitors of the DC-DC converter module are attached to the substrate of each switch-mode converter module being fabricated. For example, if an 8x8 array of DC-DC converter modules is being fabricated, then one or more dies (e.g., power supply controller integrated circuits, or switching transistors) and associated resistors, capacitors, etc. may be attached to each of the <NUM> module substrates of the 8x8 array. The components may be affixed to the substrate by solder paste, conductive adhesive, or other adhesive substance suitable for attaching electronic components to a substrate.

In block <NUM>, a sheet array <NUM> of coils <NUM>, which includes pillar interconnects <NUM>, is placed on the substrate <NUM>. The sheet array <NUM> of coils <NUM> are aligned on the substrate <NUM> such that respective substrate-based coils <NUM> are aligned with respective electronic components <NUM> from the array of electronic components <NUM>. The sheet array <NUM> of coils <NUM> are substrate-based coils that may be fabricated by methods, such as printing, etching and depositing, plating, etc., as described above and as illustrated in the flow diagram <NUM> of <FIG>. In this example however, the pillar interconnects <NUM> are pillars made from the same conductive material (e.g., copper) as the coils <NUM>. The pillar interconnects <NUM> are made by filling vias in an adjoining (fourth) dielectric layer. The adjoining dielectric layer is then removed via etching, thereby leaving only the pillar interconnects <NUM>, which are connected to respective substrate-based coils <NUM>. After the sheet array <NUM> of coils <NUM> is placed on the substrate <NUM>, the pillar interconnects <NUM> attach to substrate contacts on the substrate <NUM>. As a result, the process of depositing the substrate interconnects (e.g., solder balls) on the substrate illustrated in <FIG> can be omitted.

In block <NUM>, the array of electronic components <NUM> and the sheet array <NUM> of coils <NUM> are bonded to the substrate <NUM>. More specifically, a reflow process is performed to apply solder and heat to the pillar interconnects <NUM> to mechanically and electrically attach the array of electronic components <NUM> and the sheet array <NUM> of coils <NUM> to the substrate <NUM> via the substrate contacts. The heat may be supplied by a heat source, such as a reflow oven or an infrared lamp.

In block <NUM>, the array of electronic components <NUM> and the sheet array <NUM> of coils <NUM> are overmolded with the MMC <NUM>. The MMC <NUM> applied to encapsulate the array of electronic components <NUM> and the sheet array <NUM> of coils <NUM> may include ferromagnetic material, such as ferrite that enhances the operation of (e.g., increases the inductance of) the coils <NUM>. The MMC <NUM> also provides shielding from electromagnetic interference, and protects the electronic components of the IC from the environment.

Claim 1:
A method of fabricating integrated circuits, the method comprising:
providing a substrate (<NUM>) having an array of electronic components (<NUM>);
attaching a sheet array of substrate-based coils (<NUM>, <NUM>) to the substrate (<NUM>) where respective substrate-based coils (<NUM>, <NUM>) are aligned with respective electronic components (<NUM>);
after soldering of the substrate-based coils (<NUM>, <NUM>), encapsulating the substrate (<NUM>) having the array of electronic components (<NUM>) and the sheet of substrate-based coils (<NUM>, <NUM>) with a magnetic mold compound (<NUM>); and
singulating the array of electronic components (<NUM>) and respective substrate-based coils (<NUM>, <NUM>) to form the integrated circuits.