rf modules with embedded passives

7/28/2019 RF Modules With Embedded Passives

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Role of Wireless Modules, Using Embedded Passives, in The

Expansion of Wireless Connectivity Solutions

Mehul Udani, Jerry Kolbe

Murata Electronics North America, Inc.

2200 Lake Park Drive, GA 30080

Telephone: (770) 436-1300

Fax: (770) 436-3030

[email protected]; [email protected]

Abstract

In its press release issued January 7, 2008, Michael Foley, Ph.D., executive director of the

Bluetooth SIG is quoted as saying From prototypes in 1998 to more than 1.5 billion devices

on the market today... While this demonstrates that Bluetooth is a significant protocol forwireless connectivity, one cannot forget the cellular technologies, which are nearly

ubiquitous in todays society, WiFi, GPS or the emerging wireless interface protocols such asWiMax, UWB and Zigbee. Increasingly, wireless connectivity solutions are being deployed

across a broad spectrum of electronic equipment, whether intended for personal, business or

enterprise use, in automobiles or as a solution for medical equipment connectivity.

In todays world the phrase killer application should be plural, as the days of a device

having one wireless function are quickly passing by. Whether it is a cellular phone, a so-

called smart phone (viz.: Blackberry or Treo), PC, printer, MP3 player, or some

handheld or portable device, it is highly likely that it already incorporates a cellular interface,Bluetooth or WiFi and equally likely that it will combine several of these, as well as other,

wireless protocols in next generation equipment that will released to the market within a

couple of years time. While this may be exciting for the consumer, it poses challenges for

the Designer, as he or she must deal with a host of issues, including the co-existence of

various wireless protocols, implementation of the IC chip set reference designs, increasedcircuit density necessitating the use of smaller components, increased complexity of

functional testing and certification, reliability concerns, as well a larger bill of material cost.

Fortunately, wireless modules are serving as a cost effective, high technology solution forimplementation of one or several wireless connectivity protocols in electronic equipment.

Playing a major role in the increased attachment rate of wireless connectivity solutions inmobile devices, wireless modules incorporating Bluetooth and WiFi chipsets (for example)

are being used more frequently as Engineers are assimilating the value propositions as

compared to discrete circuit implementations. A module using a PC board material substrate

gives the user a fully tested and qualified device that features a complete RF design. A

module design utilizing a LTCC (Low Temperature Co-Fired Ceramic) substrate results in ahighly (embedded passives) integrated, miniaturized and full featured device. Whether using

PCB material base or a LTCC substrate, a RF module incorporating Bluetooth or WiFichipsets occupies significantly less motherboard real estate versus a commensurate discrete


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implementation. Comprising one device, instead of a high component count characteristic of

a discrete circuit implementation, a wireless module results in mounting cost reduction.Additionally, modules offer a solution to the barrier faced in handling, surface mounting and

testing of discrete passive components, such as ceramic capacitors and inductors, where the

state-of-the art results in increasingly smaller components bodies. Whether comprisingBluetooth, WiFi, other protocols or combinations thereof, it is forecasted that mobile devices

integrating wireless functionality will increasingly use RF modules.

This paper will discuss the role wireless modules are playing in proliferation of wirelessconnectivity solutions, the technology advantages as compared to discrete chipsetimplementations and the impact on demand for passive components.

Introduction

The iconic bicycle-riding robot, Murata Boy, utilizes Muratas own Bluetooth module to

establish a wireless communication link with a PC or mobile phone. This wireless module isjust one of the many millions shipped to the market in 2007. There are several powerful,

compelling arguments to be made for use of a wireless module to implement a wireless

connectivity function. This paper will discuss the role wireless communication modules areplaying in proliferation of wireless connectivity solutions, the technology advantages as

compared to discrete chipset implementations and the impact on demand for passivecomponents.

Before delving into why the use of a module is advantageous, it is first desirable to look intowhat makes the design and large-scale production of a wireless module possible. Integrated

Passives (IP) and Integrated Passives & Actives (IP&A) technologies for creating functional

substrates are key enablers.

Technology Enablers

Functional substrates feature embedded passive components within its structure and have

capability to incorporate active components (Integrated Circuits) on the surface and/or within

cavities. Figure 1 demonstrates this concept. Low Temperature Co-Fired Ceramic (LTCC),

PCB and silicon IPD (Integrated Passive Device) are some of the key integrated substratetechnologies currently used to realize high performance, small size modules. Each substrate

technology has unique merits, so its use is tied to the customer requirement or specificapplication. To further consider the design of a functional substrate, the example of using a

LTCC material system will be used.


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Bare chip IC

Resistor(RuO2) Thermal Vias(Ag)

Internal Conductor(Ag)

External Conductor

(Ag +Ni/Au or Ni/Pd/AuPlating)Flip chip ICChip Components

Xthlayer

3rdlayer

2ndlayer

1st layer

Bare chip IC

Resistor(RuO2) Thermal Vias(Ag)

Internal Conductor(Ag)

External Conductor

(Ag +Ni/Au or Ni/Pd/AuPlating)Flip chip ICChip Components

Xthlayer

3rdlayer

2ndlayer

1st layer

Xthlayer

3rdlayer

2ndlayer

1st layer

Figure 1: wireless communications module using highly integrated, functional substrate

In his article published in the April 2005 edition of AEI, Mr. Katsuhiko Naka of Murata

Manufacturing Co., Ltd. states Low-Temperature Co-fired Ceramics (LTCC) are multilayerglass ceramic substrates made from Ag or Cu conductors to form internal circuit traces, and

Green Sheet ceramic tapes made of a mixture of alumina base material and glass material for

form the body. The term low-temperature in the LTCC acronym refers to a firingtemperature, which at approximately 900 degrees C, is lower than alumina based ceramic,

which has a firing temperature of about 1500C. Typical properties of one of the coreLTCC material systems used at Murata are shown in table 1.

Composition Al2O3-glass

K 8.7Qf [GHz] 1,000TCC [pp m/k] 140Flexural strength [Mpa] 350Thermal expansion coefficient [ppm/k] 7.6Co-fireable electrod e AgFiring method Constrained firing

Buried Resistor RuO2 Table 1: Typical properties of a LTCC material system

LTCC MANUFACTURING PROCESS

To construct a functional substrate, the precursor of a wireless communications module,

multiple green sheet layers are utilized to construct a multilayered functional substrate. The

substrate structures are fabricated by screen-printing patterns of conductor traces onto thegreen sheets to implement passive functions. Various sheets are connected, as needed, with

silver or copper paste (depending on the LTCC material system) filled via holes. After

stacking the layers together, the substrate is fired.


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EMBEDDING PASSIVE FUNCTIONS

The passive functions that typically can be embedded into function substrates includes:

capacitor, inductor, coupler, balun, filters (BPF, LPF, HPF, diplexer), stripline and micro-stripline, as illustrated in Figure 2.

Filters Capacitors InductorsFilters Capacitors Inductors

Figure 2: 3-Dsimulation of embedded passive functions

Using LTCC, it is possible to embed typical capacitance up to 20pF and an inductance of up

to 10nH. Additionally, some substrate technologies facilitate resistor printing on the surface.For example, Muratas LFC low-temperature co-fired ceramic substrate (LTCC) functional

substrate products for automotive applications feature the capability of printing tight

tolerance, laser trimmed resistors on the surface (+/-1%, TCR +/-100ppm, 10~ 300K/area).

ACCURACY OF DESIGN SIMULATION

A key aspect in the design of a functional substrate is the capability to accurately predict the

realization of the embedded functions design. Muratas knowledge base of integrated

substrate technologies, accumulated from more than 20 years supplying high volumes ofLTCC devices and modules, PCB based VCO and PLL modules and IPD devices and

modules, has resulted in the ability to accurately predict the performance of passive function

structures during the design process. For example, figure 3 shows the testing of the low band

half of a diplexer that was constructed as a 1.675 x 1.3 [mm] LTCC device. The actualresults correlate well with that predicted by the simulation.


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Figure 3: Simulation vs. results of embedded filter function

THERMAL MANAGEMENT

When utilizing active devices to implement a wireless communications module, a keyconsideration is management of the generated heat. Functional substrates utilize metal plated

vias to dissipate thermal energy. Using Muratas LTCC technology, thermal vias can be

constructed underneath the die mount pad to manage the localized heat buildup. Using the

Murata thermal via technology, as illustrated in figure 4, we have demonstrated that the

temperature rise generated by a bare die, 2.4 GHz PA (Power Amplifier) can be lowered

from around 100C to about 65C (a 35% reduction) by optimizing the number of via holes

and their positions.


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Customer Options

The developers of end products faced with daunting challenge of implementing these

technologies as wireless technologies is becoming prevalent in modern applications. Due to

market trend, the developers are also under a time pressure of developing these products in acompressed schedule. Developers have a couple of options - either use as a Module or

discrete implementation. A module typically comprises of BB/MAC, Memory, XTAL, RF

Front-End, PA all the way to the antenna in a very small package. For example, the

Murata WiFi module represented by the block diagram shown in Figure 5 measures 8.4 x 8.2x 1.4 (h) [mm]. The module vendor takes care of the complexity and system related issuesinside the module. Discrete implementation implies the customer puts all the components

directly on their main PCB. This can be done by using package parts or using bare die.

Using a bare-die implementation of the main IC is called Chip-on-Board (CoB)implementation. CoB implementation is done primarily to enable smaller form factor.

Module Xtal(38.4MHz)

SDIO

G-SPI

VDD3.3

VDD_HOST_IO

AN T

BP F

Balun

P A

EEPROM(8kbit)

EEPROM(8kbit)

WiFi ICWiFi IC

1.8VReg.

1.8VReg.

Module Xtal(38.4MHz)

SDIO

G-SPI

VDD3.3

VDD_HOST_IO

AN T

BP F

Balun

P A

EEPROM(8kbit)

EEPROM(8kbit)

WiFi ICWiFi IC

1.8VReg.

1.8VReg.

Figure 5: Block diagram of Murata WiFi module

Due to compressed time-frame and complex technology and system level issues, a module isbecoming, more or less, a default solution of choice. Modules provide significant

advantages that translate into some obvious upfront benefits for developers, which are well

understood by the industry. However, the module also provides significant advantages,

which translate into customer savings, which are recognized later by the

production/operation team. The section below highlights these various benefits in greaterdetails.

Advantages of a Module (upfront benefits)

There are significant upfront benefits, which are recognized in the design phase of a project.

SMALLER SIZE

One of the most valued attributes of the module is that it enables a very small size. The

handheld industry has converged to smaller and thinner devices. Consumers are willing to

pay huge premiums for these smaller devices. WiFi+Bluetooth functionality can now beimplemented in 10mm x 10mm module and this module is usually thinner than 1.4mm.

LTCC technology mentioned above enables 1.2mm height module. These are significant


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technology advancements as just a few years ago these modules were 2x-3x in X-Y

dimension and height was greater than 2.5mm. The reason the module can achieve this sizeis because its typically implements use of a bare-die of the main silicon IC, such as Bluetooth

or WLAN chipset. Furthermore, this module embeds passive components into substrate

using LTCC technology described above.

REDUCING AMOUNT OF AREA OCCUPIED ON MOTHERBOARD

A big merit of using a module is the potential to reduce the area occupied on themotherboard, as compared to a discrete implementation. Figure 6 depicts the discreteimplementation of a power management circuit for a portable device. The amount of

required real estate on the motherboard (in square area) can be reduced by nearly 50%, when

using a highly integrated substrate, as shown in Figure 7.

L,C,R

0603:41pcs1005:3pcs1608:6pcs2012:5pcs

2628:2pcs

10 x 17.5 [mm]

L,C,R

0603:41pcs1005:3pcs1608:6pcs2012:5pcs

2628:2pcs

10 x 17.5 [mm]

Figure 6 : Discrete implementation

Power-I C

8.0mm

10.6mm

Power-I CPower-I CPower-I CPower-I C

8.0mm

10.6mm Figure 7 : Module implementation of circuit depicted in Figure 7

BILL-OF-MATERIAL (BOM)

Using a functional substrate, a module can be designed to replace many of the passive

components required by a discrete implementation.

Bluetooth module: up to 20 components WLAN module: up to 50 parts


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TV tuner module: up to 30 components WiMax module: as many as 200

TIME-to-MARKET

To stay competitive, OEMs are required to push out new models of their products every six

months. Because of the complexity of module is handled inside the module, it simplifies the

use of the same module across many platforms/models . This enables the designer to use a

module as an engine that enables core feature such as WLAN or Bluetooth or WiMax.Thus, the design focus is now shifted to how to design a product with product differentiationsuch as applications software, device look-feel, special features, etc. Therefore, more

engineering resources are now assigned to make use of modules as more of a black-box

technology. Furthermore, the use of the module enables more or less a cookie-cutterapproach to the design, which make it portable from one platform to another. Customers can

leverage their wireless technology implementation across multiple product lines very easily.

FASTER ADOPTION of NEW TECHNOLOGY

As mentioned, wireless standards are constantly evolved with new technology or upgrades to

new features, while maintaining the same form factor. For example, in WLAN it is

commonly referred support for alphabet soup, standards have evolved from 802.11b to

802.11g to 802.11bg to 802.11abg and now to 802.11n. In addition features, such as802.11d, 802.11e, 802.11i and 802.11p are now widely growing. Bluetooth is being evolved

into support for higher data rate (called EDR) and support for mono-and-stereo functions.

WiMax is being evolved from 802.16d (fixed) to 802.11e (mobile) and frequency bands aredifferent around the world. Mobile TV faces similar challenge where there may be single

BB (baseband) IC that can cover the protocol for supporting DVB-H, DVB-T and ISDB-T

but due to different frequency bands, the RF is different. Due to the constant evolution ofvarious technologies and the need for multiple functions (such as WiFi+Bluetooth in a single

package), module developers take the burden of incorporating various functions in their

design. This enables faster adoption of new technology into products and applications by

OEMs and ODMs. A high tier mobile may have WiFi, Bluetooth and Mobile TV functions

along with 3G Cellular functions.

Module Benefits in Customers Production Environment

There are also significant module advantages, which are recognized in Production Phase.

This is the key reason Tier 1 customers with very large volumes prefer to use module vs.

discrete/CoB implementation.

PRODUCTION CALIBRATION/TEST

One of the greatest benefit of the module is that it is fully calibrated and tested, which

eliminates the need for qualification on the production line. This allows the product to

maintain a certain level of performance consistency across large a volume of products.Furthermore, the test time of the end of product is significantly reduced, since the module

vendor takes the burden of fully testing to industry specifications. This leaves the developer

to focus on functional tests only. The elimination of calibration on the production line

eliminates the need for large capital investments required with RF test equipment and thusfurther reducing the cost of manufacturing.


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HIGHER CAPACITY UTILIZATION

As mentioned, the module incorporates a large number of components in a single very small

footprint. This directly translates to a faster assembly time on the product line. For example,the time it takes to place one WLAN module is significantly less than total time is takes to

place 40-60 components. The benefit is more important for complex technologies such as

WiMax, where more than 200 passive components are integrated into a single module. The

benefit realized by the customer is that they can manufacture more products from the sameline. This translates into operational cost savings, as well as, higher overall capacity.

LOWER PRODUCTION COST

Because of the module is fully calibrated and tested, there is no need for having experienced

engineers or expensive test equipment. Furthermore, it eliminates the need for specialized

connectors/cables on the main board in product design. Therefore, use of module reducesoverall product BOM due to high level of integration of components inside the module as

well as elimination of test points and connectors/cables. The product functional test time is

reduced which also translates in the lower production cost.

OPERATIONAL BENEFITS

The logistics of acquiring a single module is much more simplified vs. acquiring large

number of parts for discrete implementation.

Summary

Whether the substrate technology is LTCC, PCB or silicon IPD, embedding passivecomponent functions confers benefits to the user, including circuit miniaturization, fewer

components to place, reduced testing requirements and improved time-to-market, as

compared to discrete chipset implementations. Wireless modules using highly integrated,

functional substrates are playing a key role in the proliferation of wireless connectivity

solutions.

References:

1. 2008 MARKS TEN YEARS OF BLUETOOTH WIRELESS TECHNOLOGY,Bluetooth SIG, January 7, 2008

2. Using LFC Technology, Murata Makes Automotive Ceramic Substrates, AEI,April 2005, pp. 50-52.

3. S. Uozumi, N. Nakajima, H. Iwatsubo, W-LAN Module for Mobile Applicationsby LTCC Multilayer Technology, IEEE MTT-S IMS, 2004.

4. Dr. Thomas G. Reynolds, Techniques in LTCC, thin film to handle integration Technology Information,Electronic News, November 3, 1997.

Bluetooth SIG, Inc., owns the BLUETOOTH trademarks U.S.A.

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