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System-in-Package (SIP) and Embedded Component Package (ECP) for 5G Systems

方案概述

    5G has brought telecommunication technology to the upsurge and it has become the center of many
hot topics since 2018, such as IoT, AR/VR, Cloud, Big data, AI, Smart city and smart life, and autonomous
vehicles … Fast data transfer and low latency are the two key advantages of 5G technology. This makes
5G the basis for the above technologies. The implementation of 5G will generate a huge demand for
advanced packaging solutions, since these solutions can be tailored to have the right performance
features. There are many types of advanced packaging solutions, such as SIP, heterogeneous
integration, FOWLP and ECP. As a leader of electronics assembly and semiconductor assembly
equipment solution provider, K&S has solutions covering almost all advanced packaging solutions, while
SIP and ECP are the two focus points. Kana technology is the agent for K&S in these solutions. In general,
5G phones would contain 10%-20% more SIPs than 4G phones. And ECP packages is expected to prosper
in the era of 5G for the sake of its main advantages in short signal route, fast head dissipation and thin
packages.

    Figure 1: SIP Modules in 5G Phone

image.png

    There are many different definitions for SIP. One of the best might be: a fully functional subsystem
contains one or multiple IC dies (bare or packaged 2D/3D), passive components, and possibly IPDs
(integrated passive devices), ECs (embedded components), and performance enhancements (such as
head dissipation lids, shielding, and stiffeners ...). SIP is flexible in design and supply chain management,
therefore fast time to market. Traditional SIP adopts wire bonding, while advanced SIP adopts flip chip

(FC) technology. ECs normally are categorized separately from SIP although it is might be part of SIP.
Usually one advanced SIP unit contains 3 to 5 FC dies. As the advent of 5G technology, more and more
features need to be integrated into one SIP unit. SIP for 5G would contain more FC dies, generally more
than 10, or even 30 in one single unit. The first consideration in the assembly process is how to place so
many FC dies at high speed but still at competitive cost. Traditional FC bonders can handle only one type
of FC die. It is a nightmare to connect many FC bonders in a production line to handle 30 FC dies. In
addition, the quantity of FC dies varies between different models. It is not a feasible way to move FC
bonders from line to line to suit different FC quantities in different SIP models. With K&S Hybrid
placement system, passive components (mainly 01005) and FC dies can be placed consequentially in one
machine and one pass, regardless the quantity of FC dies. To do this, die sorting of FC dies from wafer to
tape and reel package is required. 15-25 microns can be achieved for FC dies placed in this way. This is
also the accuracy level required by almost all current substrate-based SIP applications. Moreover, the
placement cost of FC dies is almost the same as that of passive components.

    Among many SIP types, RF modules are pushing the assembly process capabilities to the limit. Economic
spec. for materials and machines is not a key topic anymore. What more important is to make things
done.

    Table 1An Overview Comparison between 5G RF SIP and Smart Watch SIP

RF SIP for 5G Smart Watch
Key Device FC dies, 01005, 008004 FC dies, QFN, 01005
Key process
challenges
Thin substrate and thin die
handling, 008004
Thin substrate and thin
die handling
Min. component
spacing (µm)
75-100 100-150
Accuracy
requirement (µm)
15-25 25-35

    Figure 2: Typical Layout of RF SIP (Left) and Smart Watch SIP (Right)

    image.png

    The above comparison tells us that a standard SIP unit is very similar to a common SMT product. The
technical requirements are very close to standard SMT. However, an advanced SIP product (typically RF
SIP) requires much more. The component spacing is falling beyond normal SMT process requirements,
which requires higher placement accuracy, as well as higher first pass yield to avoid impractical rework
for such high dense assemblies.

    Next main consideration in the assembly process of advanced SIP is the handling of thin substrates. Thin
substrate with warpage is very common in semi-conductor back end assembly processes. But people
who are from standard SMT plants would very probably neglect this because standard SMT do not use
vacuum support. Vast experience and data prove that a well-designed vacuum support would greatly
improve the placement accuracy and yield, especially for very high-component-density advanced SIP
units. Ensuring a good thin substrate handling is the step to return the whole process to a normal state.
For standard SIP products, a vacuum support is not so critical.

    008004 mass assembly is another challenge. It has been observed in advanced SIP products that more
than 80% passive components were 01005 from 5 years before. 01005 mass assembly is a mature
process now, but 008004 is not yet. With 5G, 008004 will be widely used in advanced SIP products.
Many equipment vendors claimed their 008004 capability in specification. But only one or two succeed
in real applications. Accuracy is the necessity but not the only factor for the success of 008004
placement. Special attention should be paid to the stencil design and printing process, as well as low
force control. The component is as thin as, and as fragile as FC dies. Only placement force control
triggered Z-stop placement process can adapt to the requirement effectively. In addition, a robust
contact detection between 008004 and substrate is quite important. It is difficult to have a real time
contact detection under high speed placement process. There is a unique feature of Hybrid system that
uses vacuum leakage detection principle to interpret a real time contact. The basic rule is that a
separate vacuum loop will be destroyed once there is a contact between the components and the
substrate. Under this special technology, component cracks are controlled at minimum.

    Figure 3: ECP Process Overview

image.png

    Embedded component packages (ECP) embed active dies and/or passive components into the base
structure of a package or a substrate/PCB. They are categorized into 4 segments depending on the
difference of base material: embedded component in laminate (substrate), embedded component in

PCB (printed circuit board), embedded component in FPC (flexible printed circuit), and embedded
interconnections in substrate. Without any printing or soldering process, ECP process need to be
integrated into a substrate/PCB/FPC manufacturing process. As a result, the main players of ECP are PCB
manufacturers. Typically, components (dies or passives) are firstly placed into cavities of a copper layer
with PP or ABF-like tape in the back, then followed by a lamination process. Next are substrate/PCB
building-up processes such as laser via, SAP, SM … In an ECP package, components are well protected in
the base material, therefore yielding a very reliable interconnection.

    ECP also has the advantages of low profile (embedded), and short signal route, which fits the
requirements of 5G applications quite well. Due to the special processes involved in the multi-layer PCB
manufacturing, ECP normally requires a very high placement accuracy for both active dies (<10 µm @ 3
σ), and passive components (<20 µm @ 3 σ). It was known in the market that Hybrid system has proven
its performance in a few tier 1 PCB manufacturers. Accuracy specification of many platforms uses a
small panel and place components in a small region. But ECP applications use very large panels (around
610mmx546mm) to achieve a good cost structure. Placement in large panels yields much lower
accuracy. As a result, the larger the test panel size and placement test region, the higher the actual
accuracy in final applications. Hybrid system uses a test panel that has the size close to ECP applications.

    Figure 4: Embedded Passives

image.png

    Figure 5: Key Features of ECP

 image.png

   ECP panel fiducials are made from bare copper with coatings, which makes the fiducial opaque and
difficult to read. In addition, special inner layer material or scratch might exist. These variations make
fiducial reading very difficult. It is not only related to the lighting capability of the camera, but also to the
algorithms of vision software. A good special modelling technique for fiducials is required.

    Figure 6: The Modelling Technique for ECP Fiducials

image.png

    Bare dies in ECP applications have unique features. They are not solder bumps or copper pillars. The
terminations are flat at the bottom, with very irregular patterns. As a result, it also demands a special
algorithm to align them. In addition, the dies are thin, in most cases 50-200µm. The handling and
placement of such thin dies is one of the top challenges in ECP processes. Force control no more than
0.5N is required. Under special circumstance, even 0.3N might be required. In a Hybrid placement
system, thin dies are handed with the same method that is applied for 008004, which has been
discussed in the above paragraph. Besides placement process, die ejecting and pickup process is also
critical. Ejector pins need to be designed as multiple contact points, and a gentle Z-moving profile is
necessary. Gentle pickup of dies is also mandatory. Hybrid systems calculated the pickup height
dynamically, thus make it possible for a gentle pickup. With a Hybrid system for ECP application, the risk
of die cracks is reduced to minimum.

    


    Reference:
1. Yole Development, 2017 and 2018 report
2. K&S Internal Estimate Jan 2019
3. Prismark/Binghamton University Report
4. “All in one Package” The Packaging Solution of the Future? AT&S (SIP China 2017)

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