Patent Application
20240332144
This application claims the benefit under 35 U.S.C. § 119(a) of European Patent Application No. 23164967.4 filed Mar. 29, 2023, the contents of which are incorporated by reference herein in their entirety.
The present disclosure relates to techniques for manufacturing a semiconductor package assembly, wherein a semiconductor die structure is mounted to a lead frame having terminals and encapsulated with a molding resin, as well as a semiconductor package assembly obtained with these techniques.
In conventional leaded/leadless power/MCD packages or power modules various connection elements are implemented for electrically and mechanically interconnecting semiconductor die structures with the various terminals of the lead frame. Examples of such electrical and mechanical connection elements are standard wire bonds, ribbon bonds or clip bonds, which requires different process steps to be applied during the power module or semiconductor package assembly manufacturing process.
Although these known connection elements are immobilized by means of an encapsulant, these fragile bonds are still prone to connectivity failures over time. In addition, these known bonding techniques are costly, complex, cumbersome and thus time consuming, as they require pre-designed and pre-manufactured connecting elements, and time-consuming handling steps for mounting these connecting elements in the manufacturing process. Also, these conventional leaded/leadless power/MCD packages or power modules still exhibit a high RDS(on) (drain-source on resistance) limiting their performance.
Accordingly, an object of the present disclosure is to provide a manufacturing technique obviating the above identified problems, resulting in a leaded/leadless power/MCD package or power module manufactured with less complex and less time-consuming process steps, and wherein the connecting elements being implemented are of a straightforward design with reduced RDS(on) characteristic.
According to a first example of the disclosure, a method for manufacturing a leaded/leadless power/MCD package or power module is proposed with less complex and less time-consuming process steps, and wherein the connecting elements being implemented are of a simple design with reduced RDS(on) characteristic.
The method comprises the steps of i) forming at least one semiconductor package by means of the sub-steps: i1) providing a lead frame made from a metal material having a first frame side and a second frame side opposite to the first frame side as well as having at least two terminals. Subsequently in a step i2) at least one semiconductor die structure is provided having a first die side and a second die side opposite to the first side, which semiconductor die structure is mounted with its second die side on the first frame side of the lead frame.
In a subsequent step i-3), one or more connection elements are provided between the at least one semiconductor die structures and the at least two terminals of the lead frame and in a final step ii) the at least one semiconductor die structure, the one or more connection elements and the plurality of terminals are encapsulated with a molding resin leaving at least a portion of at least two terminals exposed, thereby forming at least one encapsulated semiconductor package assembly.
In particular the step i3) of providing the several connection elements comprises at least one forming sequence of the sub steps of i3-1) providing a layer of a metal powder such that the metal powder is in contact with the at least one semiconductor die structure and one of the at least two terminals of the lead frame; and sub-step i3-2) of selectively melting, with laser light radiation, the layer of the metal powder to form a metal layer.
With the sequence of the two sub-steps i3-1) and i3-2), wherein the connecting elements are formed layer-by-layer through a metal powder layer deposition and solidifying, the known Cu clip bonds or Cu wire bonds are replaced and any process time for panel level packaging is significantly reduced. Furthermore, the manufacturing technique of connecting elements is more flexible compared to the known bond wire/bond clip forming techniques, which requires pre-designed and pre-manufactured components.
In addition, the layer-by-layer deposition technique implemented allows a better material handling, reducing material stresses in the connecting elements thus reducing connectivity failures over time and extending the life span of the resulting leaded/leadless power/MCD package or power module. Also, such manufacturing technique as outlined in sub-steps i3-1) and i3-2) result in a reduced (lower) RDS(on) characteristic compared to the known conventional interconnect methods. This because the whole interconnecting interface between the various components (semiconductor die structure and lead frame) will be of the same metal layer material. Solder and/or adhesive promoters between the semiconductor die structure and resulting connecting elements and between the connecting elements and the lead frame can be omitted as the metal powder connection can be fused in between the material.
In a particular example, the forming sequence of the steps i3-1) and i3-2) is performed multiple times alternately, thereby forming a three-dimensional stack of subsequent melted metal layers.
Contrary to the known pre-designed and pre-manufactured connecting elements, the method according to the disclosure allows for a more flexible layer-by-layer forming of the connecting elements as a local thickness and/or a local density of each metal layer formed during a forming sequence of the steps i3-1) and i3-2) can be effectively controlled by adjusting one or more manufacturing parameters chosen from the group of:
Effectively, the method according to the disclosure allows for each metal layer being formed in step i3-2) in having a thickness of 30-40 μm, preferably 35 μm.
The above design flexibility of the connecting elements in a layer-by-layer fashion allows in an example of the method according to the disclosure to have a surface dimension of a metal layer being larger or smaller than the surface dimension of the metal layer formed during the previous forming sequence. Herewith complex three-dimensionally shaped connecting elements can be formed depending on their functionality.
In a further example of the method, a step iii) is implemented, after a final forming sequence of steps i3-1) and i3-2) but before step ii), which step subjects the exposed portion of the at least two terminals to a surface roughening treatment, for example using a chemical agent.
Accordingly, in a further step iv), after step ii) or step iii), the exposed portion of the at least two terminals is plated with a metal plating material. Preferably, said metal plating material is Tin.
Finally, the method according to the disclosure comprises the step v), performed after step iv), of singulating the encapsulated semiconductor package from the lead frame, thereby forming a single semiconductor package assembly.
Likewise the disclosure pertains to a semiconductor package assembly composed of at least one semiconductor die structure electrically and mechanically attached by means of one or more connection elements with at least two terminals and encapsulated by a molding resin such that a portion of the at least two terminals are exposed, wherein the one or more connection elements between the semiconductor die structure and the at least two terminals are formed according to the method steps of the present disclosure.
In particular examples, the semiconductor package assembly is a leadless semiconductor package assembly or a leaded semiconductor package assembly.
The disclosure will now be discussed with reference to the drawings, which show in:
For a proper understanding of the disclosure, in the detailed description below corresponding elements or parts of the disclosure will be denoted with identical reference numerals in the drawings.
As outlined above, apart from the fragile known electrical and mechanical connection elements being immobilized by means of an encapsulant, they are still prone to connectivity failures over time. In addition, these known bonding techniques are costly, complex, cumbersome and thus time consuming, as they require pre-designed and pre-manufactured connecting elements, and time-consuming handling steps for mounting these connecting elements in the manufacturing process. Also, these conventional leaded/leadless power/MCD packages or power modules still exhibit a high RDS(on) (drain-source on resistance) limiting their performance.
The method comprises the steps of i) forming at least one semiconductor package by means of the sub-steps: i1) providing a lead frame made from a metal material having a first frame side and a second frame side opposite to the first frame side as well as having at least two terminals. Subsequently in a step i2) at least one semiconductor die structure is provided having a first die side and a second die side opposite to the first side, which semiconductor die structure is mounted with its second die side on the first frame side of the lead frame.
In a subsequent step i3), one or more connection elements are provided between the at least one semiconductor die structures and the at least two terminals of the lead frame and in a final step ii) the at least one semiconductor die structure, the one or more connection elements and the plurality of terminals are encapsulated with a molding resin leaving at least a portion of at least two terminals exposed, thereby forming at least one encapsulated semiconductor package assembly.
In particular the step i3) of providing the several electrical and mechanical connection elements comprises at least one forming sequence of the sub steps of i3-1) providing a layer of a metal powder such that the metal powder is in contact with the at least one semiconductor die structure and one of the at least two terminals of the lead frame; and sub-step i3-2) of selectively melting with laser light radiation, the layer of the metal powder to form a metal layer. The step of providing a layer of metal powder may constitute depositing the powder particles, whereas the step of selectively melting may also encompass solidifying or sintering the metal powder.
With the sequence of the two sub-steps i3-1) and i3-2), wherein the connecting elements are formed layer-by-layer through a metal powder layer deposition and solidifying, the known Cu clip bonds or Cu wire bonds are replaced and any process time for panel level packaging is significantly reduced. Furthermore, the manufacturing technique of connecting elements is more flexible compared to the known bond wire/bond clip forming techniques, which requires pre-designed and pre-manufactured components.
In addition, the layer-by-layer deposition technique implemented allows a better material handling, reducing material stresses in the connecting elements thus reducing connectivity failures over time and extending the life span of the resulting leaded/leadless power/MCD package or power module. Also, such manufacturing technique as outlined in sub-steps i3-1) and i3-2) result in a reduced (lower) RDS(on) characteristic compared to the known conventional interconnect methods. This because the whole interconnecting interface between the various components (semiconductor die structure and lead frame) will be of the same metal layer material. Solder and/or adhesive promoters between the semiconductor die structure and resulting connecting elements and between the connecting elements and the lead frame can be omitted as the metal powder connection can be fused in between the material.
In a particular example, the forming sequence of the steps i3-1) and i3-2) is performed multiple times alternately, thereby forming a three-dimensional stack of subsequent melted metal layers.
Contrary to the known pre-designed and pre-manufactured connecting elements, the method according to the disclosure allows for a more flexible layer-by-layer forming of the connecting elements as a local thickness and/or a local density of each metal layer formed during a forming sequence of the steps i3-1) and i3-2) can be effectively controlled by adjusting one or more manufacturing parameters chosen from the group of:
Effectively, the method according to the disclosure allows for each metal layer being formed in step i3-2) in having a thickness of 30-40 μm, preferably 35 μm.
The above design flexibility of the connecting elements in a layer-by-layer fashion allows in an example of the method according to the disclosure to have a surface dimension of a metal layer being larger or smaller than the surface dimension of the metal layer formed during the previous forming sequence. Herewith complex three-dimensionally shaped connecting elements can be formed depending on their functionality.
In a further example of the method, a step iii) is implemented, after a final forming sequence of steps i3-1) and i3-2) but before step ii), which step subjects the exposed portion of the at least two terminals to a surface roughening treatment, for example using a chemical agent.
Accordingly, in a further step iv), after step ii) or step iii), the exposed portion of the at least two terminals is plated with a metal plating material. For example, electroplating can be used. Preferably, said metal plating material is different from the metal material of the terminals. In an example said metal plating material is Tin.
Finally, the method according to the disclosure comprises the step v), performed after step iv), of singulating the encapsulated semiconductor package from the lead frame, thereby forming a single semiconductor package assembly.
An post-processing step may encompass a visual inspection step vi). Optionally, a step vii) is performed, before the encapsulating step ii) of providing one or more bond wires (e.g. functioning as gate wires) between the semiconductor die structure 2 and one of the other frame terminals.
As the third component, a three-dimensionally structured connecting element 31 is mounted on the first die side 2a of the semiconductor die structure 2 and is manufactured in accordance with the method steps of the disclosure. The three-dimensionally structured connecting element 31 bridges the gap or distance between the semiconductor die structure 2 and the leaded terminal 1z1 and forms an electrical and mechanical connection.
In particular, it is provided in a layer-by-layer fashion by means of the forming sequence of the sub steps of i3-1) providing a layer 30 of a metal powder such that the metal powder is in contact with the first die side 2a of the semiconductor die structure 2 and the leaded terminals 1z1 of the lead frame 1. Each layer deposition in according with sub-step i3-1) is followed by the sub-step i3-2) of selectively melting with laser light radiation L, the layer 30 of the metal powder to form a metal layer 30.
It should be note, that the step of providing a layer of metal powder may constitute depositing the powder particles, whereas the step of selectively melting may also encompass solidifying or sintering the metal powder.
Accordingly, the three-dimensionally structured connecting element 31 can be regarded as a stack of multiple metal layers 30. The forming sequence of the sub steps i3-1) and i3-2) allow a three-dimensional connecting element 31 to be structured, here in the shape of a curved bridging element, having a layered first element portion 31-a formed on the semiconductor die structure 2 and a second element portion 31-b formed on the leaded terminal 1z1 and (the first die side 2a of) the semiconductor die structure 2.
The specific three-dimensional shape of the connecting element 31 can be established in the layer-by-layer forming steps as outlined in the sub-steps i3-1) and i3-2) of the method according to the disclosure. The local thickness and/or the local material density (kg/m3) of each metal layer formed during such forming sequence of the sub-steps i3-1) and i3-2) can be effectively controlled by adjusting one or more manufacturing parameters chosen from the group of: a metal powder distribution; a supply velocity of metal powder to be deposited; a metal powder depositing angle relative to a plane formed by the lead frame; a laser light power; a laser light frequency; a laser light wavelength; an ambient process temperature; a metal powder depositing duration time of step i3-1); a metal powder melting duration time of step i3-2).
Particular parameter characteristics can be:
There are several metals that can be 3D printed using metal powder, including: stainless steel, titanium, aluminum, cobalt-chrome, inconel, copper, nickel alloys, etc. The metal powders used for creating the metal connecting elements 3 are typically created through atomization or gas atomization, and are available in a range of particle sizes and shapes to accommodate the desired circumstances for creating the metal connecting elements 3 during the subs-steps i3-1) and i3-2).
For example, with the subs-steps i3-1) and i3-2) metal connecting elements 3 can be manufactured having a porous, metal density of e.g. 60%-90%, in particular 75%-85%, more in particular 80% resulting in a more flexible interconnection which has a longer life span and which is less fragile.
In particular, the density of the metal connecting elements 3 can be controlled flexibly at different location and/or in different portions of the elements 3 with the subs-steps i3-1) and i3-2) by adjusting the printing parameter characteristics outlined above. Herewith metal connecting elements 3 can be formed with an increased electrical conductivity (high density of metal powder) or if desired reduced stress characteristics (lower density of metal powder).
Optionally, wire bonds 5 are provided between the semiconductor die structures 21 and other terminals 1z2 of the lead frame 11.
The whole package of the substrate 6, the semiconductor die structures 21, the connection elements 31, the bond wires 5, the lead frame parts 11, and the plurality of terminals 1z2 are encapsulated by a molding resin 4 (not shown), with only a portion of the terminals 1z2 exposed.
In another example, depicted in
The three-dimensionally structured connecting element 32 is being provided on the first die side 2a of the semiconductor die structure 2 in according with the method steps of the disclosure. In particular, the three-dimensionally structured connecting element 32 is provided in a layer-by-layer fashion by means of the forming sequence of the sub steps of i3-1) providing a layer 30 of a metal powder such that the metal powder is in contact with the at least one semiconductor die structure 2 and one of the at least two leadless terminals 1z2 of the lead frame 1, followed by the sub-step i3-2) of selectively melting with laser light radiation, the layer 30 of the metal powder to form a metal layer 30.
Accordingly, the three-dimensionally structured connecting element 32 can be regarded as a stack of multiple metal layers 30. The forming sequence of the sub steps i3-1) and i3-2) allow a three-dimensional connecting element 32 to be structured, formed of a layered first element portion 32-a (the main portion) formed on the semiconductor die structure 2 (and functioning as a heat sink) and a second element portion 32-b functioning as an electrical interconnect between the leadless terminal 1z2 and (the first die side 2a of) the semiconductor die structure 2.
Optionally, wire bonds 5 are provided between the semiconductor die structure 2 and another leadless terminal 1z2.
The whole construction of the semiconductor die structure 2, the connection element 32, the bond wires 5 and the plurality of terminals 1z2 are encapsulated by a molding resin 4, with only a portion of the leadless terminals 1z2 exposed.
The above design flexibility of the connecting elements being formed in a layer-by-layer fashion allows metal layers to be formed with a surface dimension 30a (see
An example with a reverse funneled shape of a connecting element 33 is shown in the example of
In all examples of the semiconductor package assemblies 101-102-103-104 shown in this disclosure, each metal layer 30 being formed with the method sub-steps i3-1) and i3-2) may have a thickness of 30-40 μm, preferably 35 μm. Additionally, a local thickness and/or a local material density (kg/m3) of each metal layer formed during such forming sequence of the sub-steps i3-1) and i3-2) can be effectively controlled by adjusting one or more manufacturing parameters chosen from the group of: a metal powder distribution; a supply velocity of metal powder to be deposited; a metal powder depositing angle relative to a plane formed by the lead frame; a laser light power; a laser light frequency; a laser light wavelength; an ambient process temperature; a metal powder depositing duration time of step i3-1); a metal powder melting duration time of step i3-2) and in accordance with the parameter ranges mentioned in connection with the description of the example of
Solder and/or adhesive promoters between the semiconductor die structure and resulting connecting elements and between the connecting elements and the lead frame can be omitted as the metal powder connection can be fused in between the material.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23164967.4 | Mar 2023 | EP | regional |
