This disclosure generally relates to flip chip packages and more particularly to thermosonically bonded flip chip packages.
Leadless (or no lead) packages are often utilized in applications in which small-sized packages are desired. In general, flat leadless packages provide a near chip scale encapsulated package formed from a planar lead frame attached to a semiconductor die. Leads located on a bottom surface of the package provide electrical connection between the semiconductor die and a substrate, such as a printed circuit board (PCB).
Typically, leadless packages include a semiconductor die or chip mounted to a die pad and electrically coupled to leads, such as by conductive wires. Improvements to make the packages thinner have eliminated the need for the die pad. In particular, chip-on-lead (COL) packages have the semiconductor die mounted directly on the leads without the die pad. The die and leads are encapsulated in an encapsulate to form the package.
Current applications for semiconductor packaging desire packages that have reduced thicknesses and a simplified connection between the die and the leads of the lead frame to reduce the volume of and increase the signal carrying ability of the package.
A method of making a package is disclosed. The method may include forming bond pads on a first surface of a substrate, forming leads in the substrate by etching recesses in a second surface of the substrate, the second surface being opposite the first surface, and plating at least a portion of a top surface of the leads with a layer of finish plating. The method may also include thermosonically bonding the leads to a die by thermosonically bonding the finish plating to the die and encapsulating the die and the leads in an encapsulant.
A semiconductor package is disclosed. The semiconductor package may include a semiconductor die having an active surface, leads having first and second opposing ends, and a finish plating on the first ends of the leads. The leads may be thermosonically coupled to the semiconductor die via the finish plating. The package may also include an encapsulant that encapsulates the die and the leads and exposes the second ends of the leads.
A method of forming chip scale packages is disclosed. The method may include forming bond pads on a first surface of a substrate and forming leads in the substrate by etching recess in a second surface of the substrate with the second surface of the substrate being opposite the first surface. The method may also include thermosonically bonding the leads to a die and encapsulating the die and the leads in an encapsulant.
The die 110 may be manufactured according to standard semiconductor manufacturing processes, and may be made of silicon or other semiconductor material. The die 110 includes an active surface 116 in which integrated circuits are formed. The integrated circuits may be analog or digital circuits implemented as active devices, passive devices, conductive layers, and dielectric layers formed within the die and electrically interconnected according to the electrical design and function of the die. For example, the circuit may include one or more transistors, diodes, and other circuit elements formed within active surface 116 to implement analog circuits or digital circuits, such as a digital signal processor (DSP), ASIC, MEMS, memory, or other signal processing circuit. The die 110 may also contain integrated passive devices (IPD), such as inductors, capacitors, and resistors, for RF signal processing.
In some embodiments, the die 110 includes a passivation layer 120 that aids in protecting the active surface 116 and the die 110 from electrical and physical damage and contamination. The passivation layer is an insulative material, such as metal oxide, and is generally very thin, on the order of 1 to 3 microns. In some embodiments, the passivation layer may be a photosensitive insulator permanent layer. The photosensitive insulator materials on the die pad may be polybenzobisoxazole (PBO) or polyimide materials and have a thickness of up to 10 um or more.
The passivation layer 120 includes openings 112 that expose bond pads 113 on the active surface 116 of the die 110. The bond pads 113 of the die 110 are coupled to the leads 224.
Each lead 224 provides an electrical and physical coupling between the die 110 and an environment outside of the package 100. Each lead 224 includes a contact pad 226 for connecting the package to another device or a substrate, such as a printed circuit board, for communication with devices external to the package 100.
Each lead 224 includes a finish plating layer 222. The finish plating layer 222 provides an interface between the die and the leads 224. The finish plating layer 222 may include one or more layers of nickel, silver, or gold deposited via an electroplating process. The electroplating process allows the finish plating layer 222 to be laid down in a very thin layer; for example, the plating layer may have a thickness that substantially corresponds to the thickness of the passivation layer 120 or may be thicker than the passivation layer. Although not shown, a patterned mask may be deposited on the second surface 232 prior to forming the finish plating layer 222 to control the application of the finish plating layer 222, as is well known in the art. After the finish plating layer 222 is formed, the patterned mask layer is removed from the second side 232 of the substrate 220.
The thickness of the finish plating layer 222 may be between 5 microns and 25 microns. In some embodiments, the finish plating layer may have a thickness of as little as 1 micron. In some further embodiments, the finish plating layer may be as much as 60 microns in thickness. In still other embodiments, the finish plating layer may be less than 1 micron in thickness.
The plating process also allows the finish plating layer 222 to be formed in various shapes, as described below with reference to
The finish plating layer 222 also aids in reducing the overall height of the package 100 and the length of the leads 224, particularly as compared to a typical stud bump connection process, which typically involves conductive bumps coupling the die to the leads in a flip chip configuration. Stud bumps formed at the top of a lead via a wire bonding process have a thickness of at least 25 to 30 microns, while a finish plating, applied via a plating process, has a thickness as small as 2.5 microns. By reducing the length of the leads and their connection to the die, the performance of the package 100 may be increased; for example, the shorter lead length may allow the die 110 to communicate with other components of an electronic device at a higher frequency, which leads to higher data transfer rates.
The package 100 further includes an encapsulant 140 that encapsulates the die 110, the finishing plating layer 222, and portions of the leads 224. The die 110 and the leads 224 are held in their respective positions within the package 100 by the encapsulant 140. The encapsulant 140 is an insulative material that protects the electrical components and materials from damage, such as corrosion, physical damage, moisture damage, or other causes of damage to electrical devices and materials. In one embodiment, the encapsulant 140 may be any suitable mold compound, such as but not limited to epoxy resin, phenolic resin, polymer, or polyester resin. The base portions of the terminal leads 224 and the contact pads 226 are left exposed from the encapsulant 140.
The leads 224 are electrically and mechanically coupled to the die 110 via a thermosonic bonding process that bonds the finish plating layer 222 to the active surface 116 of the die 110. The thermosonic bonding process uses heat, friction, and sonic vibrations to soften the finish plating layer 222 and bond it to the active surface 116 of the die 110. The thermosonic bonding process also produces an upper surface of the finish plating layer 222 that is substantially planar and more uniform than, for example, a stud bump bonding process. The substantially planar and uniform shape of the upper surface of the finish plating layer 222 formed though the electroplating process increases the strength of mechanical connection between the lead 224 and the die 110, particularly as comparted to the stud bump connection process.
Using a finish plating layer 222 thermosonically bonded to a die 110 may also allow for the use of different types of encapsulants, such as more readily available and less expensive molding compounds as compared to, for example, a package that includes a stud bump connection between the lead 224 and the die 110. Typically, stud bump connections leave narrow gaps between the top of a lead and the active surface of a die. In general, the gap is formed because the bumps are much smaller than the size of the upper surface of the lead 224. During assembly, resin or molding compound are used that can adequately flow to fill in the gaps between the top of the leads and the die and around the stud bump so that the die can be adequately supported by the encapsulant. Conversely, the finish plating layer 222 of the present disclosure are more aligned with the size and shape of the leads 224 and allow for close tolerances and accurate plating shapes, such that the gap may be reduced or eliminated. Thus, different types of resins may be used, such as more readily available and common resins and molding compounds.
As shown in
The thickness of the finish plating layer 222 may correspond to the thickness of the passivation layer 120 of the die 110, to which the final lead frame will be attached. By forming a finish plating layer 222 with a thickness that corresponds to the thickness of the passivation layer 120, the length of the leads 224 are minimized, thereby increasing the electrical properties of the lead; for example, transmitting signals at higher quality and at higher frequencies than would be acceptable with a longer lead 224.
In addition, the use of precious metals such as silver and gold have a significant impact on the overall cost of manufacturing a package such as the package 110. The precision application of the finish plating layer 222 allows a manufacturer to minimize the amount of silver and gold used to connect the lead 224 to the die 110. For example, although the upper surface 232 of the lead 224 may have a relatively large surface area, the finish plating layer 222 may be applied to less than the entire upper surface of the lead 224. For example, the finish plating layer 222 may be formed on the lead 224 in a size and shape that substantially corresponds to the size and shape of the opening 112 in the passivation layer 120 of the die 110 to which the lead 224 will be attached. It is to be appreciated, however, that the finish plating layer 222 is slightly less than the size of the opening 112 in the passivation layer 120 so that the finishing plating layer 222 fits within the openings 112. Furthermore, by substantially corresponding the thickness of the finish plating layer 222 to the thickness of the passivation layer 120 such that the upper surface of the lead 224 does not interfere with the passivation layer 120, the amount of material used in the finish plating layer 222, such as gold or silver, may be minimized.
As shown in
Although not shown, in another embodiment, the finish plating layer 222 may be blanket deposited on the entire second side 232 of the substrate 220 and then patterned. The finish plating layer 222 is etched and the substrate 220 are etched in one or more etching steps to form the channels 227 in the finish plating layer and the substrate 220 to form individual leads 224, topped with a finish plating layer 222.
As shown in
As shown in
Up until this point in the manufacturing process the substrate 220 and its bond with the die 110 and, in particular, the webbing 202 between the etched leads 224 of the substrate 220, have maintained the relative position and structural stability of the components. After the encapsulant 140 has hardened, the encapsulant 140 provides the additional structural support to maintain the relative position and structural stability of the various components, including the dies 110 and the leads 224.
As shown in
After the leads 224 are electrically isolated from each other, electrical testing may be performed on the leads and dies to check for defects as is schematically shown in
In
In
The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.
These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
Number | Date | Country | |
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Parent | 15085285 | Mar 2016 | US |
Child | 16195769 | US |