Patent Application
20160282212
The instant application relates to molded semiconductor packages, and more particularly to molded semiconductor packages with enhanced local adhesion characteristics.
Molded semiconductor packages include one or more semiconductor dies (chips) attached to a substrate and encapsulated by a mold compound. Delamination between the mold compound and a die and/or between the mold compound and the substrate allows humidity and contaminants to penetrate the package. Delamination is a particularly pressing concern for molded semiconductor packages such as sensor packages that have an open passage for permitting some form of coupling with air. For example, a pressure sensor transducer converts pressure of the air entering the passage into an electrical signal for analysis. The molding compound is much more likely to delaminate from the substrate along the interface with the open passage. To prevent delamination and humidity and contaminants from penetrating the package, adhesion between the mold compound and the package substrate should be increased, especially along the interface with any open passages. Adhesion is the tendency of dissimilar particles or surfaces to cling to one another. Adhesion is typically increased in molded semiconductor packages by pre-treating the substrate e.g. with an adhesion promoter or by surface roughening, or by adding substances to the mold compound which increase adhesion. Such approaches increase cost and may not sufficiently reduce the delamination risk over the entire operating widow (pressure, temperature) for which the package is rated.
According to an embodiment of a molded semiconductor package, the molded semiconductor package comprises a substrate having opposing first and second main surfaces, a semiconductor die attached to the first main surface of the substrate, an adhesion adapter attached to the second main surface of the substrate or a surface of the semiconductor die facing away from the substrate, and a mold compound encapsulating the semiconductor die, the adhesion adapter and at least part of the substrate. The adhesion adapter is configured to adapt adhesion properties of the mold compound to adhesion properties of the substrate or semiconductor die to which the adhesion adapter is attached, such that the mold compound more strongly adheres to the adhesion adapter than directly to the substrate or semiconductor die to which the adhesion adapter is attached. The adhesion adapter also has a surface feature which strengthens the adhesion between the adhesion adapter and the mold compound.
According to another embodiment of a molded semiconductor package, the molded semiconductor package comprises a substrate having opposing first and second main surfaces, a pressure sensor comprising a first side with a pressure sensor port facing the first main surface of the substrate, a second side opposite the first side, and electrical contacts, and a logic die stacked on the pressure sensor and comprising a first side attached to the second side of the pressure sensor and a second side opposite the first side with electrical contacts. The logic die is laterally offset from the electrical contacts of the pressure sensor and operable to process signals from the pressure sensor. The molded semiconductor package further comprises an adhesion adapter attached to the second main surface of the substrate and a mold compound encapsulating the pressure sensor, the logic die and the adhesion adapter, the mold compound having an opening defining an open passage to the pressure sensor port. The adhesion adapter is configured to adapt adhesion properties of the mold compound to adhesion properties of the substrate such that the mold compound more strongly adheres to the adhesion adapter than directly to the substrate. The adhesion adapter has a surface feature which strengthens the adhesion between the adhesion adapter and the mold compound.
According to an embodiment of a method of manufacturing a molded semiconductor package, the method comprises: providing a substrate having opposing first and second main surfaces; attaching a semiconductor die to the first main surface of the substrate; attaching an adhesion adapter to the second main surface of the substrate or a surface of the semiconductor die facing away from the substrate; encapsulating the semiconductor die, the adhesion adapter and at least part of the substrate in a mold compound, wherein the adhesion adapter is configured to adapt adhesion properties of the mold compound to adhesion properties of the substrate or semiconductor die to which the adhesion adapter is attached, such that the mold compound more strongly adheres to the adhesion adapter than directly to the substrate or semiconductor die to which the adhesion adapter is attached; and providing the adhesion adapter with a surface feature which strengthens the adhesion between the adhesion adapter and the mold compound.
Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.
The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. The features of the various illustrated embodiments can be combined unless they exclude each other. Embodiments are depicted in the drawings and are detailed in the description which follows.
According to embodiments described herein, adhesion to the molding compound of a molded semiconductor package is locally increased using an adhesion adapter attached to the substrate or semiconductor die of the package. The adhesion adapter can comprise the same or different material as the substrate, but is not an integral, continuous part of the substrate or die. Instead, the adhesion adapter is a discrete (additional) component attached to the substrate or die. The package can include more than one adhesion adapter e.g. one adhesion adapter can be attached to the bottom surface of the substrate and an additional adhesion adapter can be attached to the side of the die facing away from the substrate. In each case, the adhesion adapter is configured to adapt the adhesion properties of the mold compound to the adhesion properties of the package component to which that adhesion adapter is attached, such that the mold compound more strongly adheres to the adhesion adapter than directly to the component to which the adhesion adapter is attached.
According to the embodiment illustrated in
The molded semiconductor package 100 also includes a mold compound 114 such as silicone, epoxy, etc. which encapsulates the semiconductor die 110, the adhesion adapter 102 and at least part of the substrate 104. Leads 116, which can protrude from the mold compound 114, provide external points of electrical contact for the package 100. Electrical conductors 118 such as bond wires, ribbons, metal clips, etc. encapsulated in the mold compound 114 connect the leads 116 to terminals 120 of the semiconductor die 110. Depending on die type, the semiconductor die 110 can be glued or soldered to the substrate 104. For example in the case of a vertical transistor die 110, the bottom side 122 of the die 110 can include an output pad soldered to the substrate 104. The output pad provides a point of electrical contact for the output terminal of the transistor included in the die 110 e.g. to the drain terminal of a power MOSFET or collector terminal of an IGBT. If no electrical connection is needed at the die backside 122, the die 110 can be glued to the substrate 104 to provide a thermal connection to the backside 122 of the die 110.
Regardless of the type of semiconductor die 110 included in the molded package 100, the adhesion adapter 102 is configured to adapt the adhesion properties of the mold compound 114 to the adhesion properties of the semiconductor die 110 such that the mold compound 114 more strongly adheres to the adhesion adapter 102 than directly to the semiconductor die 110. As such, the adhesion adapter 102 locally enhances adhesion strength along the interface between the mold compound 114 and the adhesion adapter 102.
The adhesion adapter 102 can be attached to a region of the die 110 or substrate 104 where greater adhesion strength is desired. The adhesion properties adapted by the adhesion adapter 102 can include adhesion mechanisms such as mechanical adhesion, chemical adhesion, dispersive adhesion, electrostatic adhesion and diffusive adhesion, surface energy, adhesion strength and other forces that contribute to the magnitude of adhesion between the surfaces (e.g. stringing, microstructures, hysteresis, wettability and adsorption, and lateral adhesion). The adhesion adapter 102 also can have a surface feature which strengthens the adhesion between the adhesion adapter 102 and the mold compound 114. For example, grooves, single or multiple holes, notches, etc. can be formed in the surface of the adhesion adapter 102. Additional surface feature embodiments are described in more detail later herein. In general, a layer of material can be applied to the surface of the adhesion adapter 102 or the surface can be treated to strengthen the adhesion between the adhesion adapter 102 and the mold compound 114.
Because the adhesion adapter 102 is a discrete component attached to the substrate 104, the substrate 104 need not be modified to locally strengthen adhesion with the molding compound 114. This way, the substrate 104 can be manufactured using standard technologies/processes. The discrete adhesion adapter 102 adapts the adhesion properties of the mold compound 114 to the adhesion properties of the substrate 104 such that the mold compound 114 more strongly adheres to the adhesion adapter 102 than directly to the substrate 104. The local properties of the attached adhesion adapter 102 can be optimized to strengthen adhesion with the mold compound 114, without necessarily having to modify the substrate design. As such, different properties of the substrate 104 such as die or wire bond capability can be ignored since adhesion to the molding compound 114 is locally strengthened by the adhesion adapter 102. Attachment of the adhesion adapter 102 to the substrate 104 results in a topographical change of the substrate 104, which could have positive effects such as creating a barrier for unwanted humidity or chemical substances from entering the package 200 due to delamination.
In
In
In
Mold compound 928 encapsulates the pressure sensor 904, the logic die 902, the electrical conductors 924, the adhesion adapter 102, and part of the substrate 908. The mold compound 928 has an opening 930 which defines an open passage 932 to the pressure sensor port 912 of the pressure sensor 904. The part of the second surface 926 of the substrate 908 uncovered by the mold compound 928 has an opening 934 aligned with the pressure sensor port 912. External electrical contacts 936 provide points of electrical connection to the pressure sensor 904 and logic die 902 encapsulated in the mold compound 928. The logic die 902, the pressure sensor 904 and part of the electrical conductors 924 can be covered by a silicone gel 938. The silicone gel 938 is interposed between the mold compound 928 and both the logic die 902 and the pressure sensor 904 to decouple the logic die 902 and pressure sensor 904 from mechanical stress generated by the mold compound 928. Any standard silicone gel 938 can be used.
According to the embodiment shown in
According to another embodiment of the pressure sensor, one or both of the glass substrates 940, 946 are omitted and the pressure sensor 904 comprises at least the silicon die 942 with the piezo-active suspended membrane 944 over a recessed region of the silicon die 902. The recessed region of the silicon die 902 forms the pressure sensor port according to this embodiment, and is aligned with the open passage 932 though the mold compound 928 and substrate 908 to permit incoming air flow to impinge upon the membrane 944 of the silicon die 942.
In general, any standard pressure sensor 904 can be used. The pressure sensor 904 can include active device areas including transistors e.g. for sensing acceleration. The first side 910 of the pressure sensor 904 can be attached by solder, adhesive or other standard die attach material 950 to the substrate 908 which can be a die paddle (also commonly referred to as die pad) of a lead frame. The substrate 908 is partly encapsulated by the mold compound 928 so that the opening 934 in the substrate 908 aligned with the pressure sensor port 912 is uncovered by the mold compound 928 and permits incoming air flow to impinge upon the membrane 944 of the pressure sensor 904.
In the case of a lead frame die paddle as the substrate 908 to which the first side 910 of the pressure sensor 904 is attached, the external electrical contacts 936 of the pressure sensor package 900 can be leads of the lead frame. The leads 936 are embedded in the mold compound 928 at a first end and protrude out of the mold compound 928 at a second end. The leads 936 can be bent so that the second end of the leads 936 form external electrical contacts at the side of the pressure sensor package 900 opposite the pressure sensor port 912. Alternatively, the leads 936 can be bent in the other direction so that the second end of the leads 936 form external electrical contacts at the side of the pressure sensor package 900 with the pressure sensor port 912.
The mold compound 9128 is more likely to delaminate from the second surface 926 of the substrate 908 along the interface between the mold compound 928 and the substrate 908 in the region of the open passage 932, as indicated by the dashed line in
Next, the adhesion adapter 102 is separated from the periphery 1008 of the lead frame strip 1002 e.g. by stamping. The adhesion adapter 102 is then plated e.g. by submersing the adhesion adapter 102 in a plating solution 1012 to form an alloy such as Zn/Cr (e.g. A2) on the surface of the adhesion adapter 102. The alloyed adhesion adapter 102 is then attached to the bottom surface of the lead frame 1000. According to this embodiment, the adhesion adapter 102 is shaped like a flat ring which encircles an opening 1014 in the lead frame 1000 which forms a passage to a pressure sensor port of a die stack to be attached to the opposing surface of the lead frame 1000. Further standard package assembly processes are then performed such as die attach, wire bonding, glob topping, molding, etc. to yield e.g. the molded pressure sensor package 900 shown in
As previously described herein, an adhesion adapter is provided which adapts the adhesion properties of a mold compound to the adhesion properties of a substrate or semiconductor die of a molded semiconductor package and to which the adhesion adapter is attached, such that the mold compound more strongly adheres to the adhesion adapter than directly to the component to which the adhesion adapter is attached. The adhesion adapter can have a surface feature which strengthens the adhesion between the adhesion adapter and the mold compound also as previously described herein. As such, the adhesion adapter provides macro-locking with the mold compound which is a function of the overall geometry of the adhesion adapter. The surface feature of the adhesion adapter micro-locking with the mold compound which is a function of the type of surface feature used. The adhesion adapter can be attached to the die or substrate. More than one adhesion adapter can be provided so that both the substrate and die have at least one adhesion adapter. The adhesion adapter is not used to provide electrical interconnect to the die.
Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper” and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc. and are also not intended to be limiting. Like terms refer to like elements throughout the description.
As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open-ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.
With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.
