Co-packaged optical system with light-transmitting molded compound
Patent Information
- Application Number
- JP2025576738
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-07-16
- Filing Date
- 2025-07-16
- Publication Date
- 2026-09-08
Smart Images
Figure 2026530292000001_ABST
Abstract
Description
Background Art
[0001] (Cross-Reference to Related Applications) The present application claims the benefit of priority from Provisional Application No. 63 / 672,160, filed on July 16, 2024, the contents of which are incorporated herein by reference.
[0002] (Background of the Disclosure) Co-packaged optics refers to the direct integration of optical components with electrical integrated circuits (EICs) such as processing units and other application-specific integrated circuits (ASICs) to provide a package that uses a combination of electrical and optical signals for communicating and processing data. In many designs, photonic integrated circuits (PICs) are used to communicate optical data within the package, and optical fibers are generally used to relay optical data between packages. For example, an optical interface for receiving a pluggable module is used to facilitate connecting the end of an optical fiber to the package. Such an interface allows light from the fiber to be coupled into a waveguide within the PIC via a port on the surface of the PIC at the edge of the PIC. In any case, the arrangement of components within the package should provide sufficient access to the PIC to adapt the optical interface for robust and reliable attachment of the optical fiber.
Summary of the Invention
Means for Solving the Problems
[0003] This disclosure relates to circuit packages with optically accessible co-packaged optical systems and methods for fabricating such packages. In practice, the implementations herein relate to improving off-chip photon links, such as bidirectional photon links, by providing packages comprising a transparent molded compound across an in-surface optical coupler of a PIC that couples light into a waveguide within the PIC. Such molded compounds can typically facilitate optical access to the waveguide through an optical aperture smaller than the interface used to couple an optical fiber to the PIC, and / or facilitate access to the optical coupler that is close to other components within the package, including the PIC.
[0004] As will be discussed in more detail below, the embodiments described herein include a circuit package with a co-packaged optical system that includes an active element in a photon integrated circuit (PIC), such as a photodetector or modulator, and an optical path between it and an optical interface, such as a fiber array unit (FAU), connected to an optical fiber. [Brief explanation of the drawing]
[0005] [Figure 1A] Figure 1A is a schematic cross-sectional view of an exemplary system including a circuit package with a co-packaged optical system.
[0006] [Figure 1B] Figure 1B is a schematic cross-sectional view of the exemplary system shown in Figure 1A, with a heat sink.
[0007] [Figure 2] Figure 2 is a schematic cross-sectional view of another exemplary system, including a circuit package with a co-packaged optical system.
[0008] [Figure 3] Figure 3 is a flowchart illustrating a series of steps in an exemplary method for manufacturing and / or fabricating a circuit package with a co-packaged optical system. [Modes for carrying out the invention]
[0009] (Detailed explanation) Conventional circuit packages, including PICs, can be difficult and expensive to manufacture because the optical interface is a relatively large component, for example, similar in size to the PIC itself, and requires robust and precise attachment to the PIC to ensure reliable matching between the optical fiber and the coupler through which the optical signal is transmitted to and from the PIC.
[0010] One approach to managing these constraints when attaching an EIC to a PIC surface is to use an EIC die that is physically smaller than the PIC in at least one dimension. This ensures that at least a portion of the PIC surface is separated from the EIC. Waveguides within the PIC can be routed to the coupler within this portion, and optical interfaces can be attached to the exposed surface, however this manufacturing step can be difficult. Furthermore, such optical interface attachment often occurs after EIC attachment, and therefore any yield loss due to defective interface attachment often results in losses for both the PIC and the EIC, which are often the most expensive components of the package. In practice, packaging often involves encapsulating components using a molding compound, such as epoxy, which is often injection molded at high pressure. Maintaining precise alignment of the optical interface to the PIC during such a process can be challenging and may hinder the economic mass production of such packages.
[0011] However, using light-transmitting molded compounds allows for the attachment of the optical interface to the package after encapsulation of the PIC, ensuring that the optical interface is not subjected to the encapsulation process, which otherwise could expose the optical interface to significant stress, such as thermal and / or mechanical stress, and reduce yield.
[0012] Therefore, an embodiment of a co-packaged optical system is described, characterized by a PIC that is at least partially encapsulated, for example, partially or completely encapsulated, by a molded compound that includes at least a portion that is light-transmitting. The light-transmitting portion approaches one or more optical couplers within the PIC, providing optical access to the optical couplers through the molded compound.
[0013] Here, a light-transmitting compound refers to a compound that exhibits sufficient optical transmittance so that optical signals at the operating wavelength of the PIC can be transmitted through the layer of compound laminated on the PIC with sufficiently low loss to enable the delivery of optical signals to the PIC and the reception of optical signals from the PIC. In other words, a light-transmitting compound has low absorption, reflection, and / or scattering of light at the operating wavelength. The optical consideration of the optical signal through the layer of molded compound at the operating wavelength of the PIC can be 0.001 dB or more, 0.001 dB or less, 1 dB or less, for example, 0.5 dB or less, 0.2 dB or less, 0.1 dB or less, 0.05 dB or less, 0.02 dB or less, 0.01 dB or less, 0.005 dB or less, 0.002 dB or less.
[0014] Referring to Figure 1, the system 100 includes a circuit package 101 connected by a bundle of optical fibers 104 to another component 102, for example, a light source or another circuit package. Only a portion of it is shown, but the circuit package 101 includes a PIC 110, an EIC 150, an optical interface 140, and a base 132. A molded compound 134 encapsulates the PIC 110 and EIC 150 relative to the base 132, at least partially. A portion of the molded compound 134 provides a continuous flat surface 135 on which the optical interface 140 is mounted. Figure 1 also shows a Cartesian coordinate system for ease of reference. The Z direction may be referred to as the vertical direction, while the X and Y directions are lateral directions.
[0015] The optical interface 140 includes a connector for connecting a fiber connector 106 and an optical element (e.g., a lens 144) for directing light emitted from the ends of the optical fibers of the fiber bundle 104 to the PIC 110 through a portion of the molded compound 134, and / or light emitted from the PIC 110 to the ends of the optical fibers through the spacer 130. The fiber connector 106 may be detachable from the optical interface 140, or it may be permanently attached, for example, using a light-transmitting adhesive. In some embodiments, the fiber connector 106 is integrated with the optical interface 140.
[0016] The PIC110 includes a modulator 112, such as an electroabsorption modulator (EAM), a microring resonator, or any suitable optical modulator having sufficient thermal stability, and a photodetector 114, such as a photodiode. Generally, the PIC includes more than two active components, and may also include other types of active components. The PIC110 also includes grating couplers 116 and 118 located on the upper surface of the PIC110. The grating couplers 116 and 118 may be surface-relieved gratings with grating lines arranged in the lateral plane of the PIC110 to direct light incident on the normal or near-normal into the inductive modes in the planar grating. The grating coupler 116 is optically connected to the modulator 112 by a waveguide 124, and the grating coupler 118 is optically connected to the photodetector 114 by a waveguide 126.
[0017] The EIC150 is mounted in a package that overlaps a portion of the upper surface of the PIC110. The EIC150 includes a driver 152 and a transimpedance amplifier 154, which are electrically connected to the modulator 112 and photodetector 114 via electrical interconnects 156 and 158, respectively. The electrical interconnects 156 and 158 include copper columns 162 and 164, which form an electrical connection between the bottom surface of the EIC150 and the upper surface of the PIC110, respectively. Generally, the copper columns are relatively short (e.g., 100 μm or less and 50 μm or less) so that the bottom surface of the EIC150 and the upper surface of the PIC110 are close to each other within the overlapping portion. The space between the copper columns is filled with a molded compound 134.
[0018] The molded compound is made of a material that is transparent to light having wavelengths on which the optical components of system 100 operate. In other words, the amount of light absorbed and / or scattered by the layer of molded compound between the optical interface 140 and the upper surface of the PIC at these wavelengths is small enough to allow the scattering-free passage of light at these wavelengths through the spacer, and to ensure that optical signals are reliably transmitted back and forth between the PIC and the optical interface during the operation of system 100. The molded compound should also have mechanical and chemical properties that are compatible with the manufacturing process used to fabricate the circuit package 101 and compatible with the other components of the package, as well as the expected operating life of the package.
[0019] Generally, molded compounds are composite materials comprising a curable binder and one or more structural materials dispersed through the binder. The curable binder can be an organic material such as a plastic. In some embodiments, the curable binder is epoxy, acrylate, silicone, and / or urethane. The binder material can be a two-step material that hardens once the two steps are combined. In some cases, the binder is a thermosetting material or a radiation-curable material. Thermosetting materials and / or radiation-curable materials can be crosslinkable materials. Crosslinkable materials are readily flowable before hardening and solid after hardening, and once hardened, they can provide ease of handling and structural stability.
[0020] The structural material is generally a different material from the binder and may include microparticles and / or nanoparticles. In some embodiments, the structural material includes organic materials such as epoxy, acrylate, silicone, and / or urethane. In some embodiments, the structural material includes one or more inorganic materials such as Ge, Si, ZnS, ZnSe, AlO, MgF, GaAs, CaF2, and BaF2. Inorganic glasses such as BK7 and fused silica may also be used. The structural material may make up 50% by weight or more of the molded compound, for example, 60% by weight or more, 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, and 95% by weight or less.
[0021] Generally, the binder and structural materials are selected so that their optical properties are sufficiently similar to provide a transparent layer of the compound once cured. For example, the refractive indices of the binder at the operating wavelength and the refractive indices of one or more structural materials at the operating wavelength can be mismatched by less than 0.02 (e.g., less than 0.01, less than 0.005, less than 0.001, less than 0.0005, less than 0.0001). The two materials can be substantially matched indices in the operating wavelength band. The use of two or more materials can provide the ability to adjust the refractive index of the composite, for example, by varying the ratio of one material to another.
[0022] In general, in this embodiment, the vertical thickness T of the layer of molding compound across the PIC is substantially the same as or slightly greater than the vertical thickness of the EIC 150. T may range from 100 μm to 5 mm depending on the implementation. Further, in this embodiment, the top surface 135 is coplanar with the top surface of the EIC 150, but more generally, slight mismatches in surface height are acceptable provided that the surface is suitable for attachment of the interface 140. In some embodiments, the surface height may be mismatched by an amount in the range of 10 nm to 10 μm, for example, 100 nm to 1 μm.
[0023] The base 132 may include, for example, one or more interposers, redistribution layers, printed circuit boards, and / or other components used in a circuit package.
[0024] In general, the operating wavelength band of the system 100 may be one of various commonly used bands for optical communication. Generally, the operating wavelength is in the near-infrared (NIR) portion of the spectrum, for example, within 1,300 nm to 1,650 nm, and may be, for example, a C-band wavelength, that is, 1,530 nm to 1,565 nm.
[0025] In both cases, the waveguide 124, the grating coupler 116, the layer of molding compound 134, and the lens 144 form an optical path passing through the package 101 between the modulator 112 and the end of the first optical fiber in the bundle 104. During operation, the driver 154 drives the modulator 114 to modulate the optical signal in the PIC that is transmitted from the PIC 110 to the other component 102 via the first optical fiber across the optical path. The waveguide 126, the grating coupler 118, the layer of molding compound 134, and the lens 142 form a second optical path passing through the package 101 from the second optical fiber to the photodetector 114. This optical path is used to receive optical signals from the other component 102 at the photodetector 114, which then converts the optical signals into electrical signals that are detected and processed in the EIC 150 via the TIA 152. Collectively, the two optical paths provide a bidirectional photonic link between the circuit package 101 and the other component 102.
[0026] The optical interface 140, the layer of molded compound 134, and the optical couplers 116 and 118 form an interface block that facilitates the transmission of light to and from the waveguide in the fiber bundle 104 and PIC 110. Generally, the optical elements that may be included in the interface block, such as the size, length, material, and number of lenses, depend on the specific implementation requirements such as the wavelength of light, coupling efficiency, and cost. Generally, the interface block may include various mechanisms that provide an optical interface between fibers and / or between fibers and PIC, such as edge couplers, grating couplers (GC), gradient refractive index (GRIN) lens couplers, fiber Bragg grating (FBG) couplers, microlens array (MLA) couplers, evanescent wave (EW) couplers, adiabatic couplers, wavelength division multiplexing (WDM) couplers, prism couplers, butt couplers, end-fire couplers, and V-groove couplers. In some embodiments, the interface block includes a polarizing beam splitter for separating the light into orthogonal polarized states. Such beam splitters can be used to combine two orthogonal polarization signals emanating from the PIC and / or to split an unpolarized signal into two orthogonal polarization states before the signal enters the PIC. In some embodiments, the interface block includes a fiber array unit (FAU) for connecting the PIC to an array of optical fibers. For example, a fiber connector 106 and an optical interface 140 can form an FAU bonded to the surface 135 of the package 101. The FAU may be one of various types of FAUs, including linear and cyclic. A FAU is typically made from high-precision molded plastic or ceramic material and may have several to several hundred fibers, e.g., 200 or fewer fibers, 30 or more fibers, 40 or more fibers, or 80 or more fibers, arranged in a specific pattern. The selection of an FAU or FAU type may depend on the specific requirements of the application, such as the number of fibers, the arrangement of the fibers, the wavelength of light used, and the desired coupling efficiency.
[0027] As described above, the molded compound 134 encapsulates the PIC 110, EIC 150, and spacer 130 within the package 101 relative to the base 132, at least partially. In other words, the molded compound 134 encapsulates the PIC 110 and EIC 150 by filling the space between these components and the base 132, at least partially.
[0028] The EIC150, partially encapsulated within package 101, has an exposed upper surface that is coplane with the upper surface of the layer of molded compound 134, although other implementations are also possible. For example, referring to Figure 1B, in some implementations, a heatsink 130 is thermally bonded to the upper surface of the EIC150, for example, using a thermal interface material (TIM), to provide the circuit package 100'.
[0029] Referring to Figure 2, another exemplary circuit package 101 includes a layer of molded compound 234 extending across the upper surface of the EIC 150.
[0030] In general, the co-packaged optical systems described herein (with respect to Figures 1A, 1B, and 2, and below) can be used in artificial intelligence (AI) accelerators, bridges, chiplets, or any other configurations that may benefit from photon links on or outside of the package, or within the package. Embodiments may include packages with one or more EICs that share a common PIC interposer and communicate via multiple inter-chip bidirectional photon channels. Other embodiments may include circuit packages that include EICs capable of communicating with external components via multiple inter-chip bidirectional photon channels, as will be discussed in more detail herein.
[0031] In addition, it should be noted that the features and functionality of the circuit package may be implemented within various package implementations and configurations having different components and configurations. In practice, the circuit package may be implemented as part of one of various optical blocks that form part of an inter-package photon channel passing between the lattice coupler region and the optical interface (or other interface block component) and may be coplane with the upper surface of the package, for example, the upper surface of the electrical layer of the circuit package. In one or more embodiments, the circuit package is part of an optical bridge such as the one described in application No. 18 / 123,083 (which is incorporated in whole by reference), titled "Optical Multi-Die Interconnect Bridge (OMIB)".
[0032] In general, the EIC of the circuit package described above may be at least part of a memory device, computing device, storage device, or a combination thereof. Examples include, but are not limited to, random access memory (RAM) devices (such as static RAM (SRAM) devices, magnetic RAM (MRAM) devices, resistive RAM (RRAM®) devices, or conducted bridge or conducted bridged RAM (CBRAM) devices), logic devices, e.g., AND, OR, NANO, NOR, or EXOR gates, NANO flash memory, solid-state drive (SSD) memory, NOR flash memory, CMOS memory, thin-film transistor-based memory, phase-change memory (PCM), storage class memory (SCM), magnetoresistive memory (MRAM), resistive RAM, DRAM, high-bandwidth memory (HBM), DOR-based DRAM, DIMM memory, CPU, GPU, MPU, tensor engine, load / storage unit (LDSU), neural computation engine, dot product and / or convolution engine, field-programmable gate array (FPGA), Al accelerator, or any other suitable circuit elements. Multiple examples of these devices may be combined on a single die. For example, an EIC may include multiple memory arrays, one or more processors, other logic, communication circuits, and power management functions, and may include memory that executes instructions stored in the memory arrays, or otherwise interacts with the memory arrays using the processors on the EIC.
[0033] Figure 3 illustrates an exemplary manufacturing process for fabricating the package described herein, comprising a series of steps 300. In particular, Figure 3 is a flowchart comprising a series of exemplary steps for fabricating and mounting the circuit package 100'. Alternative embodiments may omit, add to, rearrange, and / or modify any of the steps shown in Figure 3. The steps in Figure 3 may be carried out as part of a method (e.g., a method for fabricating a circuit package). In one or more embodiments, one or more machines may perform one or more of the steps in Figure 3 with the help of a processor and computing devices.
[0034] A series of steps 300 includes step 310, which involves placing a photon integrated circuit (PIC) across the carrier base. For example, step 310 involves placing a photon integrated circuit (PIC) across the carrier base. The PIC includes one or more photon channels.
[0035] The EIC is attached to the PIC on the surface of the PIC, facing the carrier base (320). The EIC can be, for example, flip-chip bonded to the PIC, and components within the EIC can be electrically connected to components within the PIC via copper columns.
[0036] The EIC and PIC are encapsulated by a molding compound (330). Typically, the encapsulation process involves injection molding an uncured molding compound around the PIC and EIC at high pressure, followed by curing the compound. Depending on the implementation, the molding compound can be cured by a variety of possible mechanisms, including the use of two-step epoxy, thermosetting, or chemical radiation.
[0037] A portion of the hardened molded compound is removed, for example, by grinding and / or polishing (340). This process exposes the upper surface of the EIC and ensures a planar surface of the layer of molded compound across the optical coupler in the PIC.
[0038] The heatsink is attached to the exposed surface of the EIC (350). For example, the heatsink can be attached using thermal paste to ensure good thermal bonding at the interface.
[0039] The optical interface is attached to the surface of the molded compound (360) after matching the optical interface with the optical coupler in the PIC.
[0040] The embodiments described above feature a co-packaged optical system (CPO) in which the EIC is bonded to the surface of the PIC. More generally, the packaging techniques described herein can be applied to other CPO systems in which the optical path is provided through a layer of molded compound. For example, in some embodiments, multiple EICs (e.g., one or more processor units and / or one or more memory units) can be bonded to a single PIC. In some embodiments, electronic components can be integrated into the PIC rather than in (or in addition to) a separate EIC. For example, drivers and / or TIAs can be integrated into the PIC. Also, while the embodiments described above show an array in which light is internally or externally coupled to the PIC via the surface of the PIC, other coupling schemes are also possible. For example, edge coupling can be used. In such embodiments, the optical path for light from the coupled fiber can traverse a transparent molded material at the edge of the PIC.
[0041] The following numbered paragraphs are non-limiting embodiments of the innovative embodiments of the present disclosure.
Claims
1. Integrated circuit package, A photon integrated circuit (PIC) comprising an active element and an optical coupling element arranged to receive light on the surface of the PIC and couple the light into one or more waveguides within the PIC, wherein the active element is located within a first portion of the PIC, and the optical coupling element is located within a second portion of the PIC, spaced apart from the first portion. A molded compound that at least partially encapsulates the PIC, wherein the layer of the molded compound covers the surface of the PIC in the second portion, and Equipped with, The molded compound in the second portion is transparent to light in the operating wavelength band of the PIC, and the layer of the molded compound, the optical coupling element, and one or more waveguides provide an optical path for light in the operating wavelength band to the active element through the package.
2. The package according to claim 1, further comprising a first electrical integrated circuit (EIC) electrically connected to the PIC.
3. The package according to claim 2, wherein the first EIC is attached to the surface of the PIC, overlapping with the first portion and not overlapping with the second portion.
4. The package according to claim 3, wherein the first EIC is at least partially encapsulated by the molding compound.
5. The package according to claim 4, wherein the surface of the first EIC facing away from the PIC is at least partially free of the molding compound.
6. The package according to claim 5, further comprising a heat sink supported by the first EIC on the surface in which the molded compound is at least partially absent.
7. The package according to claim 3, further comprising a second EIC attached to the surface of the PIC and overlapping with a further portion of the PIC not overlapped by the first EIC, or with a second portion of the PIC.
8. The package according to claim 1, further comprising an optical interface for optical fibers, which is attached to the surface of the layer of the molded compound.
9. The package according to claim 8, wherein the optical interface is attached to the surface of the layer of the molded compound by an optical adhesive, and the molded compound comprises the optical adhesive.
10. The package according to claim 8, wherein the optical interface comprises a fiber array unit (FAU).
11. The package according to claim 1, further comprising an optical interface attached to the molded compound on the surface of the layer of the molded compound facing the PIC, wherein the optical interface comprises a connector for receiving at least one optical fiber and one or more optical elements arranged to direct light in the operating wavelength band from the optical fiber to the optical coupling element.
12. The package according to claim 11, wherein the optical interface includes a polarization beam splitter for splitting an optical signal into a pair of signals having orthogonal polarization states, or for combining a pair of orthogonally polarized optical signals exiting the PIC, prior to the pair of optical signals entering the PIC.
13. The package according to claim 11, wherein the one or more optical elements include at least one focusing element for focusing light through the spacer to the optical coupling element.
14. The package according to claim 11, wherein the optical interface comprises an array of lenses, at least one of the lenses in the array corresponds to one or more optical elements arranged to direct the light in the operating wavelength band from the optical fiber to the optical coupling element.
15. The package according to claim 1, wherein the molded compound comprises a plastic material.
16. The package according to claim 15, wherein the plastic material is a thermosetting plastic material.
17. The package according to claim 15, wherein the plastic material is epoxy.
18. The package according to claim 15, wherein the plastic material comprises an optical adhesive.
19. The package according to claim 18, wherein the optical adhesive is epoxy, acrylate, silicone, or urethane.
20. The package according to claim 15, wherein the plastic material is a single-component plastic material.
21. The package according to claim 15, wherein the plastic material is a multi-component plastic material.
22. The package according to claim 15, wherein the molded compound further comprises an inorganic component.
23. The package according to claim 22, wherein the inorganic component comprises nanoparticles and / or microparticles.
24. The package according to claim 23, wherein the inorganic component comprises silica.
25. The package according to claim 23, wherein the inorganic component constitutes 50% by weight or more of the molded compound.
26. The package according to claim 23, wherein the inorganic component comprises particles composed of a compound selected from the group consisting of Ge, Si, ZnS, ZnSe, AlO, and MgF.
27. The package according to claim 23, wherein the refractive index of the plastic material at the operating wavelength and the refractive index of the inorganic component at the operating wavelength are mismatched to 0.02 or less.
28. The package according to claim 1, wherein the PIC further comprises a demultiplexer in the optical path between the optical coupling element and the active element.
29. The package according to claim 28, wherein the active element is a photodiode or a modulator.
30. The package according to claim 1, wherein the PIC further comprises a multiplexer in the optical path between the optical coupling element and the active element.
31. The package according to claim 1, wherein the optical path is part of a bidirectional photon channel between a first EIC and an external component of the package, and the bidirectional photon channel comprises the first optical path and a second optical path between another optical coupling element and another active element.
32. The package according to claim 31, wherein the first EIC comprises an application-specific integrated circuit (ASIC).
33. The package according to claim 31, wherein the first EIC comprises a memory interface.
34. The package according to claim 1, wherein the operating wavelength band includes the C band.
35. A method for fabricating an integrated circuit package, To provide a photon integrated circuit (PIC) comprising an active element and an optical coupling element arranged to receive light on the surface of the PIC and couple the light into one or more waveguides within the PIC, wherein the active element is located within a first portion of the PIC, and the optical coupling element is located within a second portion of the PIC, spaced apart from the first portion. The molded compound encapsulates at least a portion of the PIC within the molded compound such that a layer of the molded compound covers the surface of the PIC in the second portion. Includes, The molded compound in the second portion is transparent to light in the operating wavelength band of the PIC, and the layer of the molded compound, the optical coupling element, and one or more waveguides provide an optical path for light in the operating wavelength band to the active element through the package, in a method.
36. The method according to claim 35, wherein encapsulating the PIC includes injection molding an uncured molded compound around the PIC, and curing the uncured molded compound to provide the molded compound.
37. The method according to claim 36, further comprising removing a portion of the molded compound to provide a planar surface of the layer of the molded compound.
38. The method according to claim 37, wherein removing the portion of the molded compound exposes the surface of an electrical integrated circuit (EIC) electrically connected to the PIC.
39. The method according to claim 38, further comprising attaching a heat sink to the exposed surface of the EIC.
40. The method according to claim 35, further comprising attaching an optical interface to the surface of the layer of the molded compound.
41. The method according to claim 40, wherein the optical interface is attached using an optical adhesive.
42. The method according to claim 41, wherein the optical adhesive is identical to at least the components of the molding compound.
43. To provide electrical integrated circuits (EICs), The EIC is attached to the surface of the PIC, Encapsulating at least a portion of the PIC while encapsulating at least a portion of the EIC using the molding compound. The method according to claim 35, further comprising: