This application relates to producing a flexible substrate for integrated circuit packaging, and more particularly, to producing a cyclo-olefin polymer flexible substrate for integrated circuit packaging and biocompatible sensors.
With the rapid growth of the 5G network as a telecommunication standard for future devices, electronic devices are expected to operate based on a millimeter scale wave length (mm wave) in the frequency range of 30-300 GHz. Such a system offers a vast amount of bandwidth for high data rates which is particularly attractive for the Internet of Things (IoTs), Advanced Driver Assistance Systems (ADAS), Massive Multiple-Input Multiple-Output (MIMO), and the like. To enable these applications, a massive amount of communications between devices are required. Meanwhile, mm waves operating at high frequencies possess unique propagation behavior compared to typical RF (radio frequency) signals. Consequently, challenges arise for the architecture and packaging of telecommunication systems with a major focus on minimizing transmission loss. At such a short wavelength, the physical dimensions of electronic packages and interconnects become significant as they act as a transmission line, contributing to signal loss. For example, a bond pad becomes capacitive, a wire bond becomes inductive, and so on. Hence, reducing form factor is not only desirable for product miniaturization but is also beneficial to reduce the aforementioned signal losses. This gives rise to integrating devices directly on a substrate such as Antenna-in-Package (AiP) and integrated passive devices (IPDs) to fully benefit from the smaller form factor.
Flexible electronics have emerged as promising solutions for device miniaturization as they provide numerous advantages including higher circuit density, thinner profile, lighter weight, and shape conformance capability (foldable and bendable) as compared to their rigid counterpart of printed circuit board (PCB). In terms of processing, flexible electronics also offer competitive cost and efficiency due to their reel-to-reel manufacturing capability.
Base film substrate material plays a significant role in signal transmission characteristics. Low dielectric constant and loss tangent is desired to minimize insertion loss while low relative permittivity is required to decrease latency (signal delay). Owing to the sensitivity of mm wave performance with respect to material properties, the choice of dielectric material becomes more stringent.
With the increasing awareness of health more than ever before, wearable electronic devices for health care monitoring have also been growing rapidly. Wearable devices offer an attractive approach to medical diagnostics by providing remote health monitoring. It allows healthcare personnel to monitor physiological signs of patients in real time and to provide assessment of the health conditions remotely.
Among many health condition parameters, biopotentials such as electrocardiogram (ECG), electroencephalogram (EEG), electromyogram (EMG), electrooculogram (EOG), etc which measure the electrical output of human body activity from different body parts are excellent indicators of health condition. For example, an ECG signal indicates heart activity by measuring the electrical current induced by depolarization and repolarization that occur on a cardiac cycle (heartbeat) which is useful to detect various cardiovascular diseases (CVD). To detect this electrical current, sensing electrodes are required to be attached directly onto human skin at different locations. To enable non-invasive long term health monitoring, this biosensor has to be conformable with skin (biocompatible) and mechanically flexible.
Conventionally, a silver/silver chloride (Ag/AgCl) wet electrode with conductive gel has been used for biopotential sensors. Despite its excellent signal acquisition performance, a wet electrode suffers many drawbacks especially for wearable devices and long term monitoring. First, the application of wet electrodes require skin preparation which typically requires medical personnel. Second, the conductive gel dries out over time which degrades the signal quality and thus needs to be changed frequently which leads to the aforementioned problem. Finally, the conductive gel might cause irritation to skin, allergic reactions, inflammation, etc. Therefore, a dry electrode without the need of a conductive gel is a more suitable alternative for wearables and a long term monitoring system. Using a biocompatible flexible substrate and a noble metal as the contact electrode, a dry electrode that conforms to the skin can be used as a biopotential sensor. With direct contact between the skin and the noble metal, less signal noise resulting from skin motion artifacts can also be achieved.
U.S. Patent Applications 2016/0378071 (Rothkopf), 2018/0248245 (Okada), and 2020/0117068 (Yamazaki et al) include COP substrates. U.S. Patent Application 2016/0369812 (Narita et al) discloses a flexible substrate.
A principal object of the present disclosure is to provide a method of producing a flexible substrate for a semiconductor package having superior low loss characteristics.
Another object of the disclosure is to provide a method of producing a cyclo-olefin polymer flexible substrate for a semiconductor package having superior low loss characteristics.
A further object of the disclosure is to provide a method of producing a cyclo-olefin polymer flexible substrate for a semiconductor package having superior low loss characteristics and a method of directly metallizing the COP surface.
Yet another object is to provide a method of producing a cycl-olefin polymer flexible substrate for integrated circuit packaging of communication devices using direct metallization of the COP surface.
A still further object is to provide a method of producing a cycl-olefin polymer flexible substrate for use in biocompatible sensor devices.
According to the objects of the disclosure, a method to produce a flexible substrate is achieved. A base film material of cyclo-olefin polymer (COP) is provided. A surface of the COP base film is irradiated with UV light to form a functional group on the COP surface. Thereafter, the surface is treated with an alkaline degreaser. Thereafter, a Ni—P seed layer is electrolessly plated on the surface. A photoresist pattern is formed on the Ni—P seed layer. Copper traces are plated within the photoresist pattern. The photoresist pattern is removed and the Ni—P seed layer not covered by the copper traces is etched away to complete the flexible substrate.
Also according to the objects of the disclosure, another method of manufacturing a flexible substrateis achieved. .A base film material of cyclo-olefin polymer (COP) is provided. A surface of the COP base film is selectively irradiated with UV light to form a functional group in a pattern on the COP surface. Thereafter, the surface is treated with an alkaline degreaser. Thereafter, a catalyst is deposited on the irradiated pattern on the surface. Thereafter, copper traces are plated on the catalyst to complete the flexible substrate.
Also according to the objects of the disclosure, a method of manufacturing a semiconductor package for a millimeter scale wavelength communication module is achieved. A flexible substrate with an embedded antenna is provided as follows. A base film material of cyclo-olefin polymer (COP) is provided. A surface of the COP base film is irradiated with UV light to form a functional group on the COP surface. Thereafter, the surface is treated with an alkaline degreaser. Thereafter, a catalyst is deposited on the surface and, thereafter, copper traces and an embedded antenna are plated on the catalyst to complete the flexible substrate. A surface finishing layer is plated on the copper traces but not on the embedded antenna and at least one electronic component is mounted on the flexible substrate.
Also according to the objects of the disclosure, a method of manufacturing a semiconductor package is achieved. A base film material of cyclo-olefin polymer (COP) is provided. A surface of the COP base film is irradiated with UV light to form a functional group on the COP surface. Thereafter, the surface is treated with an alkaline degreaser. Thereafter, a catalyst is deposited on the surface. Thereafter, copper traces are plated on the catalyst to complete the flexible substrate. A surface finishing layer is plated on the copper traces and at least one electronic component is mounted on the flexible substrate.
Also according to the objects of the disclosure, a method of manufacturing a biocompatible flexible substrate is achieved. A base film material of cyclo-olefin polymer (COP) is provided. A surface of the COP base film is irradiated with UV light to form a functional group on the COP surface. Thereafter, the surface is treated with an alkaline degreaser. Thereafter, a Ni—P seed layer is electrolessly plated on the surface. A photoresist pattern is formed on the Ni—P seed layer. Biocompatible surface finishing is plated within the photoresist pattern. The photoresist pattern is removed and the Ni—P seed layer not covered by the biocompatible surface finishing is etched away to complete the biocompatible flexible substrate.
Also according to the objects of the disclosure, another method of manufacturing a biocompatible flexible substrate is achieved. A base film material of cyclo-olefin polymer (COP) is provided. A surface of the COP base film is selectively irradiated with UV light to form a functional group in a pattern on the COP surface. Thereafter the surface is treated with an alkaline degreaser. Thereafter a catalyst is deposited on the irradiated pattern on the surface. Thereafter a Ni—P seed layer is electrolessly plated on the surface. Thereafter biocompatible surface finishing is plated on the Ni—P seed layer to complete the biocompatible flexible substrate.
In the accompanying drawings forming a material part of this description, there is shown:
Cyclo-Olefin Polymer (COP) emerges as a promising material to fulfill future device requirements with superior low loss characteristics compared to high performance materials such as liquid crystal polymer (LCP), modified polyimide (MPI), polyimide (PI), and polyethylene terephthalate (PET). In addition, COP also offers excellent properties in terms of chemical resistance, water adsorption, gas permeability, and light transmission. On the other hand, conductor roughness is also critical to minimize the signal loss as skin effect (tendency of current to be distributed near the conductor surface) becomes more significant as signal frequency increases. Therefore, forming a smooth conductor surface on top of the COP material as a circuitry pattern is an attractive electronic packaging solution to minimize both dielectric and conductor losses which are essential for 5G devices. Directly metallizing the COP surface also opens up fabrication of integrated devices such as Antenna-in-Package (AiP). Furthermore, due to its unique optical properties, COP can also be integrated with optical interconnect for applications involving high volume data transmission.
COP suffers from a low melting temperature that limits the processing capability and subsequently its potential to be used in electronic packaging as the assembly process of electronic components typically requires a high temperature that degrades the COP. Overcoming these challenges will enable COP to be used as a superior packaging substrate for future communication devices.
The present disclosure describes the construction and fabrication method using cyclo-olefin polymer (COP) base film material that is flexible and possesses low dielectric constant/loss tangent and excellent biocompatibility, thus is suitable for both IC Packaging of Communication Devices (mmWave) and Biocompatible Sensors Devices.
Referring now to
Now, as shown in
Next, the surface is treated with an alkaline degreaser in a typical cleaning process. Now, a catalyst layer, not shown, is deposited onto the irradiated surface 12 of the COP base 10 by immersion into an ionic metal solution. Typically, Palladium (Pd) or Nickel (Ni) is deposited to activate the surface for subsequent electroless Ni—P plating. As shown in
As shown in
In
The photoresist layer 16 is stripped, as shown
A protective layer of surface finishing is preferably plated on top of the copper circuitry. For example,
This completes formation of the traces on the flexible substrate. The manufacturing method described results in an extremely smooth surface with RA <25 nm without compromising trace adhesion. This smooth surface is able to minimize the conductor loss during signal transmission. Trace adhesion strength and bend durability is similar to, if not better than, that of a substrate fabricated by a conventional subtractive process using a sputtering type base film material.
The second preferred embodiment of the present disclosure is described with reference to
Now, the COP surface is selectively irradiated by means of a photo mask/direct imaging technique using UV light to alter the resin surface and create a functional group as shown by 18 in
Next, a catalyst is deposited by immersion into an ionic metal solution. Typically Palladium(Pd) or Nickel (Ni) is deposited to activate the surface for subsequent electroless plating. The catalyst 20 deposits only on the irradiated pattern 18, as shown in
As shown in
In some applications, autocatalytic nickel-phosphorus (Ni—P) as a seed layer can be applied over the UV irradiated COP film using an electroless plating process prior to the electroless copper plating. In this case, the Ni—P thickness is ideally 0.1 μm+/−10%. The composition of Ni—P in the seed layer is Ni: 96.5˜97.5 wt %, P: 2.5˜3.5 wt %. In some applications, the Ni—P can be in a different ratio and the thickness can be in the range of 0.1-1.0 μm.
This completes formation of the traces 22 on the flexible substrate. As in the first embodiment, the manufacturing method of the second embodiment results in an extremely smooth surface with RA <25 nm without compromising trace adhesion, This smooth surface is able to minimize the conductor loss during signal transmission. Trace adhesion strength and bend durability is similar to, if not better than, that of a substrate fabricated by a conventional subtractive process using a sputtering type base film material.
A protective layer of surface finishing is preferably plated on top of the copper circuitry. For example,
After completing the formation of traces on the flexible substrate according to either the first or the second preferred embodiment, a semiconductor package for a mmwave communication module may be manufactured. The traces may form an embedded antenna design. The surface finishing layer 24 should not be formed on the embedded antenna.
Electronic components are assembled onto the flexible substrate.
The assembly method for both the first level of device to package and the second level of interconnect of the package to the main board can be using low temperature interconnect materials to prevent degradation on the COP material. These materials can include low melting temperature solder metallurgy, conductive adhesive film (such as anisotropic conductive film, isotropic conductive film, or non-conductive film), or curable printed conductive ink.
After completing the formation of traces on the flexible substrate according to either the first or the second preferred embodiment, a semiconductor package may be manufactured. Electronic components are then assembled onto the flexible substrate.
The assembly method can be using low temperature interconnect materials to prevent degradation on the COP material. These materials can include low melting temperature solder metallurgy, conductive adhesive film (such as anisotropic conductive film, isotropic conductive film, or non-conductive film), or curable printed conductive ink.
Furthermore, a biocompatible flexible substrate can be provided according to the present disclosure. A third preferred embodiment of the present disclosure will be described with reference to
Fabrication continues as described for the first embodiment with irradiating the COP surface using ultra-violet (UV) light to alter the resin surface and create a functional group 12, as shown in
As shown in
Now, referring to
Next, as illustrated in
In a fourth preferred embodiment of the present disclosure, an alternative method of fabricating a biocompatible flexible substrate is described with reference to
Now, the COP surface is selectively irradiated by means of a photo mask/direct imaging technique using UV light to alter the resin surface and create a functional group as shown by 18 in
Next, a catalyst is deposited by immersion into an ionic metal solution. Typically Palladium(Pd) or Nickel (Ni) is deposited to activate the surface for subsequent electroless plating. The catalyst 20 deposits only on the irradiated pattern 18, as shown in
Now, referring to
Finally, as shown in
The biocompatible flexible substrates of the third and fourth embodiments can be used in medical devices, medical patches, medical imaging/diagnosis devices, implantable biomedical devices, or lab-on-flex.
The present disclosure has described a method of manufacturing a flexible substrate for a semiconductor package with superior signal transmission performance or a biocompatible flexible substrate especially useful for high frequency for Internet of Things (IoTs), sensors (smart home, smart packaging, autonomous driving), smart wearables (virtual reality/augmented reality (VR/AR), electronic skin, wearable patch), optoelectronics (data storage, data transmission, communication modules), medical devices (medical patch, medical imaging/diagnosis devices, implantable biomedical devices, lab-on-flex), and industrials (building & machinery monitoring/automation).
Although the preferred embodiment of the present disclosure has been illustrated, and that form has been described in detail, it will be readily understood by those skilled in the art that various modifications may be made therein without departing from the spirit of the disclosure or from the scope of the appended claims.