SiSonic Design Guide

Transcription

1 SiSonic Design Guide

2 Table of Contents 1.0 MEMS MICROPHONE TECHNOLOGY CHOOSING THE RIGHT SISONIC MODEL MICROPHONE SIZE AMPLIFIED SISONIC AND APPLICATIONS DIGITAL SISONIC SISONIC DESIGN MATRIX MECHANICAL DESIGN CONSIDERATIONS CHOOSING LOCATIONS FOR THE MICROPHONE AND CASE PORT HOLE ACOUSTIC PATH DESIGN EXTENDING THE MICROPHONE FREQUENCY RESPONSE PREVENTING ECHO PCB LAND PATTERNS ELECTRICAL DESIGN CONSIDERATIONS POWER SUPPLY GROUND GAIN CONTROL MICROPHONE TO CODEC INTERFACE CIRCUIT ELIMINATING RF/EMI NOISE MANUFACTURING INFORMATION PICK-AND-PLACE SETTINGS REWORK HANDLING AND STORAGE QUALIFICATION TESTING SENSITIVITY MEASUREMENTS ADDITIONAL RESOURCES... 29

3 1.0 MEMS MICROPHONE TECHNOLOGY SiSonic MEMS microphones are the cutting edge of acoustic technology and are gaining wide acceptance in many types of consumer electronics products including cell phones, smart phones, PDAs, digital still cameras, IC recorders, laptop PCs, and tablet PCs. The principle of operation for SiSonic microphones is the same as for traditional Electret Condenser Microphones (ECMs), but because the microphone is manufactured using silicon wafer processes it lends itself to smaller form factors, has improved performance under severe conditions, and is easier to designin. Purpose: This application note outlines the features of each SiSonic model and assists design engineers in selecting the right microphone and designing it into their application. 2.0 CHOOSING THE RIGHT SISONIC MODEL SiSonic microphone models vary by package type and by the functions which are integrated into the microphone. Choosing the microphone package depends primarily on the mechanical requirements of the design, while the need for additional functions is driven by the application. The information in this section will help you choose the right SiSonic microphone model for your application. A diagram of the basic components in a SiSonic microphone is shown below.! Figure 1: The basic components of a SiSonic microphone

4 2.1 MICROPHONE SIZE The two main aspects of size are footprint and height. The footprint determines the PCB area used by the microphone, and the height affects the overall design thickness. Nominal dimensions and pictures of the SiSonic package types are shown below. Package Type Standard (Legacy) Zero-Height Zero-Height (Next Gen) Mini Mini (Next Gen) * preliminary Length 6.15 mm Width 3.76 mm Height 1.45 mm * * Footprint 23.1 mm Table 1: SiSonic Package Dimensions Package Type Top View Standard (Legacy) Zero-Height Mini 6-pad Mini (Next Gen) Table 2: SiSonic Package Types Bottom View

5 Standard and Mini SiSonic are top-port microphones. Zero-Height SiSonic microphones have a bottom-port and are particularly suited for thin designs. The diagrams below show typical gasket and case design configurations using each type of microphone. Product case Standard Height PC B Top-port SiSonic Microphone Figure 2: Typical design using a top-port Standard or Mini SiSonic microphone Gasket Product case Minimized Height PCB Zero-Height SiSonic Figure 3: Typical design using a bottom-port Zero-Height SiSonic microphone Gasket 2.2 AMPLIFIED SISONIC AND APPLICATIONS In far-field applications like teleconferencing or video recording, the desired acoustic signal comes from a distance and requires additional amplification. Amplified SiSonic microphones boost the microphone output signal with up to 20dB of additional gain before transmitting it to the CODEC. Amplifying the signal at the microphone compared to amplifying the signal at the CODEC improves the overall system Signal-to-Noise Ratio (SNR). Care must be taken to match the amplified audio signal with the dynamic range of the CODEC input. Many camera phones and video phones have multiple use models that may include both nearfield and far-field modes. Switchable Gain SiSonic (SPM0207 series) allows the designer to switch between near-field (non-amplified) and far-field (amplified) modes simply by asserting/de-asserting the High Gain Switch pin on the microphone. The separate near-field and far-field microphones common in some designs can be replaced with a single switchable gain microphone. Figure 4 illustrates a typical switchable gain circuit.

6 6 - VDD Output _ R1 = 22k R2 = 2.44k N.C. 4 - Ground 2 Gain Control 3 High Gain Switch R3 (set by customer) C1 (set by customer) V switch Figure 4: Switchable Gain SiSonic Block Diagram SiSonic is also available with a differential output driver that offers an amplified output and stronger noise immunity due to the common mode rejection of noise picked up in the output traces. Figure 5 illustrates a typical differential circuit.

7 6 - Vdd Preliminary + - R1 = 9.8K R2 = 2.44k 2 - Output- 1 - Output+ 4 - Ground 3- Gain Control R3 (set by customer) C1 (set by customer) Figure 5: Block Diagram of Differential SiSonic with Amplified Output 2.3 DIGITAL SISONIC Digital SiSonic microphones have an ADC integrated into the microphone. The primary advantage to a digital microphone interface is noise immunity. Only extreme noise can cause a bit change in a digital signal, and the modified Pulse Density Modulated (PDM) format used makes the audio signal relatively immune to even multi-bit errors. The digital microphone accepts a 1.0 MHz to 3.25 MHz clock from the chipset, and returns over-sampled PDM data at the supplied clock frequency, with decimation and filtering performed in the interface chipset. An L/R select signal enables the microphone to drive the data line on either the rising edge (left) or falling edge (right) of the clock, such that two mics can multiplex data over the same trace for stereo recording. A basic block diagram of a Digital SiSonic design is shown in Figure 6.

8 " L L/R to Vdd for L L/R to Gnd for R Clock ( MHz) Data (PDM format) " R Figure 6: Digital SiSonic Interface L/R outputs can be multiplexed on same data line DSP Interconnectivity is dependent on the chipset and your chip-set vendor can assist in compatibility. Contact Knowles for the latest product information on the new digital SiSonic microphones.

9 2.4 SISONIC DESIGN MATRIX The table below summarizes the design needs, features, packages, and applications of the various SiSonic packages. Design Requirement SMD reflow microphone Thin design Standard (legacy) package Zero- Height Mini 6-pad Mini X X X X X Benefit/application Mounted in standard lead-free solder reflow processes Bottom-mount design allows zero height requirements on top side of PCB Small footprint X X Minimal use of board space Amplified output Switchable gain Differential output Digital interface X X X X Table 3: Summary of Design Needs met by SiSonic X X X Far-field applications, improved system SNR Covers both near-field and farfield applications Better noise immunity from balanced design Best noise immunity, no ADC necessary in chipset, ideal for stereo recording applications SiSonic microphones are available with and without built-in RF protection. Contact Knowles for additional information and specific model numbers.

10 3.0 MECHANICAL DESIGN CONSIDERATIONS The purpose of this section is to provide mechanical design guidance around the microphone including: Selecting the mic location Selecting the acoustic port hole size and location Configuration of acoustic gasket interface PCB solder pad layout Note: The interface circuit for the microphone is covered under Electrical Design. 3.1 CHOOSING LOCATIONS FOR THE MICROPHONE AND CASE PORT HOLE As a general principle, the microphone and its interface circuitry should be located away from antennas, power amplifiers, motors, hard disk drives, switching power supplies, and other potential EMI noise sources. It is also desirable to keep the trace length from the microphone output to the codec input short to further decrease the chance of noise from EMI. The layout engineer must choose a location for the microphone while considering additional factors such as the available board space on the top and bottom of the PCB, the possible locations for the port hole in the case, the component height restrictions on each side of the PCB, and the required gasket design for each potential location. The location for the acoustic hole in the case should be chosen far enough from speakers and other acoustic noise sources so that the strength of these unwanted signals is minimized at the microphone input. In near-field applications like normal talk mode in a cell phone, the port-hole location is more critical since small changes in distance can significantly affect the strength of the acoustic signal arriving at the microphone. Close mouth-to-mic spacing yields the best SNR. In far-field applications the port-hole location has little effect on the strength of the acoustic signal. In both types of applications, the port hole should be located such that it won t be blocked by a finger or other object during normal use. Picking a good location for the microphone and case port hole early in the design process helps prevent costly layout changes later on. 3.2 ACOUSTIC PATH DESIGN The acoustic path is important because it guides sound into the microphone, and its design can significantly affect the frequency response characteristics of the microphone. The physical dimensions of each part of the acoustic path (case, gasket, and PCB) together with the standalone microphone frequency response determine the overall frequency response of the microphone in the design. A short, wide acoustic path has minimal effect while a long, narrow path can pull the higher frequency peak and roll-off into the audio band, potentially causing a tinny sound. A good acoustic path design gives a flat sensitivity frequency response across the target acoustic

11 frequency range. The designer must check the frequency response of the microphone and acoustic path together and make adjustments if the performance doesn t meet design goals. Adjustments could include: 1. A larger case hole or thinner case 2. A wider gasket port 3. A shorter acoustic path by changing the mic or case hole location 4. A larger or thinner PCB hole 5. Adding a screen or mesh as an acoustic resistance to extend the flat frequency response range (covered in detail in a later section) The codec or baseband chipset input should include a low-pass filter with a cutoff frequency just above the desired acoustic range to remove the unwanted higher frequency components of the audio signal. The frequency response curves below show the sensitivity of the standalone microphone, the microphone with a short, wide acoustic path design (gasket A), the microphone with a long, narrow acoustic path design (gasket B), and both designs with a 3.5kHz brick wall filter meant to be representative of a typical codec low-pass digital filter Mini SiSonic Simulation Data Mini with gasket A Mini with gasket B Gasket A with 3.5kHz Filter Gasket B with 3.5kHz Filter Sensitivity (db) Frequency (Hz) Figure 7: The Effect of Acoustic Path Design on Microphone Frequency Response

12 !"! #! $!!!%!$ &! %'!"(!! )"$*!(! #!! %! (!!$ *! %(!%$ Case Port Hole Gasket Cavity Product case Standard Height PCB Noise Mini SiSonic Figure 8: A Simple, Effective Acoustic Path Design for a Top-Port Microphone Optional Screen Microphone Port Hole +,!!!!!(%-./!-./$&-./! (! # )" ( (!!%!!!(% -./! $&-./!(!!%!%!(! $A simple acoustic path design for a bottom-port SiSonic microphone is shown below. Product case Minimized Height Noise Case Port Hole Gasket Cavity PCB Zero-Height Noise SiSonic PCB Port Hole Microphone Port Hole Figure 9: A Simple, Effective Acoustic Path Design for a Bottom-Port Microphone Optional Screen Knowles provides free simulation services for acoustic path designs. These simulations show the approximate frequency response of SiSonic microphones with the gasket, case, and PCB to show if the frequency response is appropriate for the application. A summary of some of the recommended minimum dimensions for SiSonic acoustic path design is shown in the table below. Case holes and gasket ports can be non-circular, and will give similar performance as a circular hole with the same cross-sectional area as long as the dimensions aren t extreme.

13 Microphone Package Microphone Port-hole diameter Minimum PCB Hole Diameter Gasket Diameter Port Case Hole Diameter Standard (Legacy) 1.02 mm N/A > 1.52 mm > 1.0 mm Mini 0.84 mm N/A > 1.34 mm > 1.0 mm Zero-Height 0.76 mm 1.0 mm > 1.5 mm > 1.0 mm Table 4: Recommended Acoustic Path Dimensions Once the physical dimensions of the gasket are determined, then the material and manufacturability of the gasket must be considered. The gasket material must block acoustic signals, and must provide a good seal between the microphone and product case, or in the case of Zero-Height microphones, between the PCB and case. A good seal prevents echo and component noise problems that are typical of gasket leaks, and requires. To make a good seal, the gasket must be thick enough to be compressed under the worst case conditions of microphone or PCB to case spacing. Side-port or end-port gasket designs are more difficult, since the required gasket compression force is parallel to the surface of the microphone and parallel to the usual direction of the case compression force as shown in the figure below. These types of gaskets can have problems with leaks during the product assembly process, but a good mechanical design and assembly process can address this issue. Product case Usual Case Compression Force End-port Gasket Mini SiSonic PCB Potential gasket leak Figure 10: Example of an End-port Gasket Design Optional Screen Common gasket materials include various kinds of rubber and compressible, closed-cell foam. Knowles can design and source gaskets for SiSonic microphones, so if you are interested in these services please contact your local Knowles representative for more information.

14 3.3 EXTENDING THE MICROPHONE FREQUENCY RESPONSE Applications such as music recording require a flat microphone frequency response to frequencies well above the voiceband of typical wireless applications. The SiSonic frequency response can be extended beyond the voiceband by adding acoustically resistive material to the acoustic path of the microphone that will flatten the peak in the frequency response. This material is a screen or mesh that blocks a significant percentage of the acoustic path area, or a porous sheet of material that resists but allows airflow. Designers using SiSonic can send acoustic resistance samples to Knowles for testing to determine the effect on microphone frequency response. Two materials tested by Knowles had good acoustic damping characteristics as shown in the frequency response curves below. An optimized gasket design together with an acoustic resistance could extend the frequency response range of the microphone to almost 20 khz, as shown in the last two curves below Simulation of Mini SiSonic and gasket 1 Mini, gasket 1, screen 1-20 Mini, gasket 1, and screen 2 Sensitivity (db) Mini, gasket 2 (optimized) Mini, gasket 2, screen Frequency (Hz) Figure 11: Using an Acoustic Resistance Screen to Extend the Flat Frequency Response An acoustic resistance can be inserted almost anywhere in the acoustic path with similar effect: between gasket and microphone (top-port microphones only), gasket and case, or PCB and

15 gasket (bottom-port microphones only). Examples of possible screen locations are shown in Figures 8, 9, and 10. An acoustic resistance screen also functions as a dust guard, and if it is made of hydrophobic materials can also help prevent liquid from entering the microphone if the application requires it. The thickness of the screen, typically 0.2mm or more, must be taken into account when determining the height stack-ups and compression of gasket materials. 3.4 PREVENTING ECHO If there is an echo problem in a design, the most likely cause is a poor gasket seal that allows sound to travel inside the product casing from the speaker to the microphone. Since this sound travels in an enclosed space, it does not decrease significantly with distance and can be quite strong when it reaches the microphone. An easy way to test for a gasket leak is to block the acoustic port hole in the case. If the echo problem is still there, then the echo is likely caused by a gasket leak and can be fixed by a gasket design change. In addition to echo, a gasket leak may also cause the microphone to pick up audio noise from other sources such as the zoom motor on a camera module. The figure below shows a design with a gasket leak. Product case Noise from speaker, motor, etc. PCB Figure 12: Echo or noise from a gasket leak Mini SiSonic Gasket Leak In some applications like conference calls the speaker output must be strong, and extra care must be taken to prevent the speaker signal from causing echo in the microphone signal. Assuming a good gasket design between the microphone and case, the strength of the speaker output at the microphone input is determined by the shortest path from the speaker to the microphone for sound traveling outside of the product case. The strength of the speaker output in open air decreases proportionally to 1/R. Once again, blocking the case port hole of the product can help determine if this is the source of echo. If the echo disappears when the case port hole is blocked, then the speaker signal is too strong when it reaches the microphone input. An external echo path such as this can be fixed by: 1. Decreasing the speaker output strength. 2. Increasing the path length sound must travel from speaker to microphone until the echo is reduced to an acceptable level, usually by changing the location of the microphone and/or speaker in the design.

16 3. Using echo canceling software such as the Knowles IntelliSonic software, which includes active echo cancellation that can reduce echo by up to 40 db. IntelliSonic also includes noise cancellation and beam-forming for 2 microphone arrays that can further improve echo performance and decrease the strength of other background noise signals, significantly improving SNR. Contact Knowles for further information about IntelliSonic. 3.5 PCB LAND PATTERNS The recommended PCB land pattern for each SiSonic model is included in the data sheet, and is generally exactly the same size and shape as the pads on the microphone. (Data sheet dimensions are given in millimeters, but since the actual specs are in inches some minor discrepancies in the least significant digit of dimensions may arise.) Customers may optimize the pad dimensions for their own design rules and needs. Zero-Height microphones have a unique land pattern because of the bottom-port design. As discussed in the Acoustic Path Design section above, a design using a Zero-Height microphone requires an unplated hole through the PCB that has a diameter of at least 1.0 mm. The recommended land pattern for the solder pad around the port hole has a slightly larger diameter hole in it, so that there is a small buffer zone of solder mask around the port holes that helps keep solder balls from forming at the edges of the holes. In preparation for reflowing SiSonic, a solder stencil pattern, solder paste, solder thickness, reflow profile, and pick location must be selected. The recommended solder stencil pattern for SiSonic is generally the same as the PCB land pattern layout, with the exception of the port-hole solder pad of Zero-Height models. Zero-Height microphones should not have solder paste applied over the port hole of the PCB, so have a modified recommended stencil pattern as shown below. See the specifications for each SiSonic model for detailed dimensions.

17 (a) (b) Figure 13: Comparison of Zero-Height SiSonic recommended PCB land pattern (a) and recommended solder stencil pattern (b)

18 4.0 ELECTRICAL DESIGN CONSIDERATIONS SiSonic microphones have separate power and output pads and may have additional pads for other integrated functions, so require different interface circuitry from traditional ECMs. Both analog SiSonic and ECMs have small amplitude output signals that are susceptible to noise, and care should be taken with the electrical design since a good approach can avoid potential problems later on. This section outlines recommendations for designing the interface to each pad of SiSonic, with an emphasis on the interface between the microphone output and the codec. 4.1 POWER SUPPLY SiSonic microphones have no change in sensitivity across the power supply voltage range specified in the data sheets. Because SiSonic has a separate power supply line and an internal voltage regulator, it is less susceptible to power supply noise than traditional ECMs. Testing has shown that the Power Supply Rejection Ratio (PSRR) of SiSonic nearly 50dB for non-amplified models and nearly 30 db for amplified models that are configured with the maximum 20dB of additional gain. Even with this strong attenuation of power supply noise, the resulting noise in the microphone output may be significant. For example, a 10mV RMS noise signal at 1 khz in the power supply will still cause a 30V RMS ripple in the microphone output of a nonamplified SiSonic. This is significant compared to the 11V RMS typical noise floor of the microphone, and is equivalent to an SNR of 48dB or an acoustic input of about 46dB SPL. If noise in the microphone power supply is strong, then shunt capacitors may be added to the microphone power supply to further attenuate noise. Designers may choose to add a low frequency capacitor in the F range and an RF capacitor in the pf range to remove audible and RF noise, respectively. Adding a series resistor before these capacitors will make a single-pole low-pass filter circuit. Other types of low-pass filter circuits are possible. If a series resistor is used, care must be taken that the DC drop across the resistor with the maximum microphone current draw still guarantees the 1.5V minimum supply required by the microphone. In general, noise outside the acoustic range does not cause problems for the microphone output signal as long as there are no frequency components in the acoustic range. 4.2 GROUND The microphone ground pad should be connected to the analog ground plane in the design. A good ground has a short, direct trace to a large ground plane and is not daisy-chained from device to device, and is as clean as possible. If there is noise in the ground plane, some evidence suggests that adding a ferrite bead in the ground path can help isolate the microphone output from the noise. Some SiSonic packages have two or more ground pads including the solder pad around the port-hole of Zero-Height microphones. Only one ground connection is necessary for

19 SiSonic, but it is good design practice to connect all microphone ground pads to ground in the PCB layout. 4.3 GAIN CONTROL The gain of amplified SiSonic microphones is set using a resistor and capacitor connected to the Gain Control terminal of the microphone, as shown in the circuit below. Term 4 = V+ Vout R1 = 22kΩ Term 1 = Output R2 = 2.4kΩ Term 3 = Ground Term 2 = Gain Control R3 (set by customer) C1 (set by customer) Figure 14: Gain control circuitry for amplified SiSonic The value of R3 sets is chosen to give the desired gain value (up to 20dB for R3 = 0). C1 is necessary to allow proper DC biasing of the amp input, and is chosen so that the corner frequency (C.F.) of the high-pass filter formed by C1, R2, and R3 is well below the acoustic range. A C.F. near 100 Hz is common. For the maximum gain of 20dB, simply connect the Gain Control terminal to ground through a 0.47 F capacitor. If no additional gain is required, the gain terminal can be tied directly to the output terminal for the same sensitivity as a nonamplified SiSonic. The gain terminal should never be left unconnected since it will act as an antenna and pick up noise. R3 and C1 can be calculated using the following formulas:

20 Setting Gain Formulas: Gain of non-inverting Op-Amp is determined as: G=1+ {R1 / (R2 + R3)} Gain (db) = 20 * log(g) High-pass-filter Corner Frequency: C.F. = 1 / {2*pi*(R2 + R3) * C1} Figure 15: Formulas for calculating gain control component values The R and C components should be located as near to the microphone as possible, since any noise picked up in the Gain Control terminal is fed almost directly into the output of the microphone. In harsh RF environments, adding a series ferrite bead very close to Gain Control terminal can significantly reduce RF noise. 4.4 MICROPHONE TO CODEC INTERFACE CIRCUIT The interface circuit between the SiSonic microphone output and the codec or baseband chipset can range from simple to more complex depending on the design needs. If the chipset used includes DC bias circuitry, then the only component required is a series coupling capacitor, typically in the F range, and even this can be excluded if the DC output level of the microphone (typically 0.9 to 1.2V) matches the requirements of the codec. In most cases a coupling capacitor is needed, and some chipsets require an external DC bias circuit after the coupling capacitor. Consult your chipset documentation for the recommended audio interface circuit, but remember that SiSonic microphones should not have an external pull-up resistor from the output to power since they have a separate power terminal. In general, the output trace should be kept as short as possible, and should be routed over or sandwiched between analog ground planes to help prevent EMI noise from entering the audio signal. Since the output impedance of SiSonic is less than 100, virtually 100% of the output signal is seen at the input to the codec. The figure below shows a simple microphone interface circuit.

21 &)(,-(.,(, # '(0%)(1 "$ " &'()%)('*+ # % / / Figure 16: Example of a simple SiSonic interface circuit 4.5 ELIMINATING RF/EMI NOISE Some product designs like cell phones have harsh noise environments where RF noise sources such as antennas and power amplifiers may be close to the microphone. RF frequency signals are not themselves a problem since they are well above audio frequencies, but many wireless standards use TDMA technologies where data is sent in bursts or packets. The frequency of these packets usually falls in the audio range and can induce an undesirable buzz in the audio signal. In designs where RF noise is a concern, there are a number of techniques a designer can use to protect the audio signal from picking up RF/EMI noise. 1. During layout, the microphone and output traces should be located as far as possible from RF noise sources. 2. Components connected to the microphone should be placed very near the microphone to minimize trace lengths that can pick up noise. (DC coupling capacitors and any RF components at the codec input are exceptions.) 3. Capacitor(s) can be added to the microphone power trace if the microphone bias signal is noisy. SiSonic has very good PSRR, but strong noise in the microphone power line may still require filtering. 4. The microphone output trace length should be kept to a minimum, and the output should be routed over or sandwiched between ground planes. Series ferrite beads and RF shunt capacitors can be used to reduce RF noise in the traces.

22 5. Differential SiSonic can be used to remove common mode noise picked up by the output traces. Differential output traces can be designed for single-ended SiSonic by using the output and ground as two sides of a differential pair. 6. The microphone and associated circuitry can be placed in shielded areas of the design to reduce the potential for RFI and EMI. &)(,-(.,(, # "$ / '(0%)(1 6&'()%)'*+ /7& 8)%6 82 +(( / # % " &'()%)('*+ / &)'%)'' / / Figure 17: Single-ended SiSonic design with RF/EMI protection techniques

23 &)(,-(.,(, # # "$ % / '(0%)(1 6&'()%)'*+ /7& 8)%6 82 +(( / # % " &'()%)('*+ / &)'%)'' / / Figure 18: Differential SiSonic design with additional RF/EMI protection techniques With increasingly stringent test standards and smaller phone designs, many of these techniques may be needed to guarantee that a high-quality acoustic signal at the codec input.

24 5.0 MANUFACTURING INFORMATION SiSonic microphones are surface mount microphones that are installed with standard pick-andplace machinery and reflowed onto a PCB with other surface mount components. Because SiSonic microphones are significantly different from traditional ECMs, they have some unique requirements in an assembly line. 5.1 PICK-AND-PLACE SETTINGS SiSonic microphones come in various size reels for use in auto pick-and-place machines. Exact packaging information including pocket size and spacing is shown in each model s specification. The pick location for top-port models should be chosen so that the pick nozzle does not ever overlap the port-hole of the microphone, while considering microphone and pocket tolerances and the pick nozzle shape, size, and placement accuracy. Bottom-port models may be picked anywhere on the lid. The recommended pick area for the Mini SiSonic package is shown in the figure below. Figure 19: SPM010xNx3 Mini SiSonic Pick-up Area.

25 SiSonic microphones have gold-plated solder pads and are designed for use with lead-free solders but may also be used with lead-based solders. The recommended solder stencil thickness is mm minimum to mm maximum. SiSonic is guaranteed for up to 3x passes through a lead-free solder reflow profile, and manufacturing line samples are tested weekly with 5x reflows at the maximum profile conditions as part of On-going Reliability Tests (ORTs). The exact reflow profile should be selected based on design requirements, but should not exceed the maximum reflow profile for the microphone shown below: C 230 C Pre-heat 120 sec. Solder Melt 100 sec. Figure 20: SiSonic maximum solder reflow profile SiSonic microphones are installed in the reflow processes of the production line, much earlier than traditional ECMs, and as a result the downstream processes in the production line must be reviewed to ensure that they do not damage the microphone. 1. No liquid should enter the port hole of the microphone. Board washes after the microphone installation must either be eliminated or modified to ensure that no liquid enters the port hole of the microphone. 2. No strong air flow or vacuum pressure should be applied to the microphone. Any board blow-off procedures must be reviewed to insure that the blow nozzle is not directed into the microphone port-hole. 5.2 REWORK Rework of Sisonic microphones is recommended using a temperature-ramp controlled system such as an A.P.E. Chipper. The local area around the microphone can be heated until solder reflow allows the microphone to be removed with a vacuum nozzle or tweezers. Installation of a new microphone component is recommended using the same reflow profile used to install the

26 original component. Please see the SiSonic rework document for details on the recommended rework process. 5.3 HANDLING AND STORAGE Information on handling and storage for Sisonic microphones is listed below: 1. Shelf life: Twelve (12) months when devices are to be stored in factory supplied, unopened ESD moisture sensitive bag under maximum environmental conditions of 30ºC/70% R.H. 2. Exposure: Devices should not be exposed to high humidity, high temperature environment. MSL (moisture sensitivity level) Class 2A. 3. Out of bag: Maximum of 90 days out of ESD moisture sensitive bag, assuming maximum conditions of 30ºC/70% R.H. If unused portions of reels are placed in static bags for storage, these bags must not be vacuum sealed since a strong vacuum force can damage the microphones. 5.4 QUALIFICATION TESTING SiSonic microphones give very consistent performance under extreme conditions. They are resistant to power supply noise, mechanical shock, temperature, humidity, moisture condensation, and vibration, and have no sensitivity variation over the specified supply voltage range (typically 1.5 to 5.5V). A comparison of SiSonic and a typical ECM is shown for many of these characteristics in the following table, and a graph of the vibration sensitivity of SiSonic vs. a typical ECM is shown in the figure after that. Feature SiSonic ECM PSRR > 40dB (typical ~50dB), 20 db < 5dB (typical 1dB) less for amplified models Mechanical Shock >10,000 G <5,000 G typical Temperature -40 C to +105 C -25 C to +85 C Vibration Sensitivity ~ -74dBv/G ~ -62dBv/G Change in Sensitivity with Voltage No loss down to 1.5v Max 3dB Loss at 1.5v Table 5: SiSonic and ECM performance comparison

27 Sensitivity (dbv/g) SiSonic ECM ECM w/ Gasket Frequency(Hz) Figure 21: Vibration Sensitivity Comparison of SiSonic and a typical ECM SiSonic microphones are lead-free compliant and are certified Sony Green, and all Knowles facilities are ISO certified. SiSonic microphones also undergo a regular battery of Ongoing Reliability Tests (ORTs) to ensure consistent quality microphones. Additional testing is performed for the qualification of new designs and to verify that process changes do not affect the reliability of the microphone. These additional tests are outlined in the table below: Test Description Thermal Shock Microphone unit must operate when exposed to air-to-air thermal shock 100 cycles, from 40ºC to +125ºC. (IEC ) High Temperature Storage Microphone unit must maintain sensitivity after storage at +105ºC for Test 1,000 hours. (IEC Test Ba) Low Temperature Storage Microphone unit must maintain sensitivity after storage at 40ºC for Test 1,000 hours. (IEC Test Aa) High Temperature Microphone unit must operate within sensitivity specifications for Operating Test 1,000 hours at 105ºC. (IEC Test Ba)

28 Low Temperature Operating Test Humidity Test Microphone unit must operate within sensitivity specifications for 1,000 hours at 40ºC. (IEC Test Aa) Tested under Bias at 85ºC/85% R.H. for 1,000 hours. (JESD22- A101A-B) Vibration Test Microphone unit must operate under test condition: 4 cycles, from 20 to 2,000 Hz in each direction (x,y,z), 48 minutes, using peak acceleration of 20 G (+20%, -0%). (MIL 883E, method , A) Electrostatic Discharge Reflow Mechanical Shock Bend Testing Moisture Sensitivity Table 6: SiSonic Qualification Tests 5.5 SENSITIVITY MEASUREMENTS Tested to 8kV direct contact discharge to lid as specified by IEC , level 3 and level 4. Microphone is tested to 5 passes through reflow oven, with microphone mounted upside-down under conditions of 260ºC for 30 seconds maximum. Microphone must operate after exposure to shock test of 10,000 G per IEC , Ea. Test board bent ±4mm across 50mm span. Rate from 0 to ±2mm is 62.5mm/min.; ±2mm to ±4mm is 2.5mm/min. Dwell at ±4mm is 5 sec. 168 hrs. at 85ºC/85% R.H. storage, followed by 3 passes through 260ºC reflow within 4 hours of removal from storage. The most accurate sensitivity measurements are made in an anechoic chamber, where an acoustic signal from a speaker is captured by the test microphone in a noise-free environment, and a reference microphone is used to calibrate out any non-linearities of the speaker and chamber. During final test in the SiSonic production lines, sensitivity is measured on 100% of microphones using a brass box that isolates microphones from environmental noise and reference microphones that guarantee accurate measurements. Knowles can also provide Portable Test Jigs (PTJs) to customers for quick sensitivity measurements on individual microphones using an oscilloscope or multimeter to measure the microphone output. An output (V O ) measured in RMS volts can be converted to sensitivity (S) in db using the formula S = 20*log(V O /1V). See the Portable Test Jig User s Guide for more information on sensitivity measurements using PTJs.

29 6.0 ADDITIONAL RESOURCES For more information on SiSonic microphones, see the Knowles Acoustics web site at or contact your local Knowles sales office listed at the end of this document. Date: April 20, 2006 Version: AMERICAS: Knowles Acoustics 1151 Maplewood Drive Itasca, IL U.S.A. Phone: Fax: EUROPE: Knowles Acoustics York Road, Burgess Hill West Sussex, RH15 9TT England Phone: Fax: JAPAN: Knowles Acoustics Kyodo Bloom Building Miyasaka, Setagaya-Ku, Tokyo , Japan Phone: Fax: ASIA: Knowles Acoustics 5F, No. 129, Lane 235, Bauchiau Rd. Shindian City, Taipei 231, Taiwan Republic of China Phone: Fax: