TECHNICAL INFORMATION

SURFACE MOUNT

by Phil Elliott AVX Corporation 5701 E. 4th Plain Blvd. Vancouver, Washington 98661

Abstract:

Ceramic resonators provide an attractive alternative to quartz crystals for oscillation frequency stabilization in many applications. Their low cost, mechanical ruggedness and small size often outweigh the reduced precision to which frequencies can be controlled, when compared to quartz devices. Ceramic resonators are now available in surface mountable packages suitable for automated production processes. SURFACE MOUNT CERAMIC RESONATORS

by Phil Elliott AVX Corporation 5701 E. 4th Plain Blvd. Vancouver, Washington 98661

Ceramic resonators provide an attractive alterna- tive to quartz crystals for oscillation frequency stabilization in many applications. Their low cost, parallel F a mechanical ruggedness and small size often outweigh 10k operating the reduced precision to which frequencies can be range controlled, when compared to quartz devices. +90 Impedance Ceramic resonators are now available in surface 1k mountable packages suitable for automated produc- ) degrees tion processes. ␾ The equivalent electrical circuit of a is -90 Impedance (Z), ohms shown in Figure 1 and typical values for the equiva- 100 Phase ( Phase lent circuit elements of a 455kHz and 4MHz resonator series resonanceFr are shown in Table I. operating point 10 Frequency (Hz)

Motional Arm Figure 2. Impedance and Phase response C0 L0 R0 of ceramic resonators

Ceramic resonators are generally operated in the parallel resonance mode. This allows the use of an inverting or logic inverter which provides

C1 180° of phase shift. The combination of the resonator, Shunt Arm in the inductive portion of its response curve, and the load provide the balance of the 360° of Figure 1. Resonator equivalent circuit phase shift around the oscillator loop needed to main- tain oscillation. In addition the gain of the amplifying device must be sufficient to maintain a loop gain The resonant and anti-resonant frequencies are greater than or equal to unity to sustain oscillation. related to the equivalent circuit parameters by the The oscillation frequency specified for a particular following expressions, where Fr is the resonant resonator is the frequency at which the device will frequency and Fa is the anti-resonant frequency as operate when used with a specific shown in Figure 2. and with appropriate load capacitors. The reference IC used by AVX/Kyocera is a MC14069 (Hex invert- F = 1 er). If the resonator is used with another type of IC r 1/2 2␲ (L0C0) or with load capacitors different to those used in the reference circuit then the oscillation frequency may Fa = 1 differ slightly from the nominal value. In many cases 1/2 2␲ (L0C0C1/(C0+C1)) the frequency can be “trimmed” back to the desired frequency by adjusting the load values or otherwise modifying the oscillation circuit. Advice on resonator circuit design with many com- monly used ICs can be obtained from the reference document, “Application circuits of ceramic res- P/N Freq. R0 L0 C0 C1 Qm onators”, available from AVX/Kyocera. For special Ω µH pF pF applications it is possible to obtain resonators which KBR-455Y 455kHz 8.8 4700 28 315 1380 have been matched to a particular IC to improve the frequency tolerance and operating performance. 1 PBRC-4.00A 4.0MHz 4.8 310 5.6 44 1500 Figure 3 shows a typical oscillator circuit using a 1same as PBRC-4.00B (with built-in capacitor) ceramic resonator. The inverter and buffer could be discrete logic elements or the “on chip” oscillator cir- TABLE I. Typical equivalent circuit parameters cuit of a microcontroller. The user has the option for 455kHz and 4.0MHz ceramic resonators many frequencies of using a resonator which has the load capacitors built into a single three terminal pack- Frequency age. This permits a reduction in component count and deviation associated board space usage. Reference temperature = 25°C +0.6

Inverter Buffer +0.4 2-terminal device +0.2

0 Resonator C1 C2 C1 C2 -0.2 Load capacitors 3-terminal device KBR-480Y (load capacitors built in) -0.4 480kHz ceramic resonator Figure 3. Typical resonator oscillator circuit and -0.6 functional circuits of 2 and 3 terminal (built in load capacitors) resonators -40-20 0 20 40 60 80 100 120 It should be noted that ceramic resonator fre- Temperature, °C quency tolerance is quoted by the manufacturer at a temperature of 25°C, when used with the reference Frequency IC as mentioned previously. In addition to the fre- deviation quency tolerance a temperature stability is also quot- Reference temperature = 25°C ed, usually over a temperature range of -20 to +80°C. +0.6 A typical value for the tolerance at 25°C is ±0.5% although for applications such as telephone DTMF +0.4 tone generation it is possible to produce resonators matched to a particular IC which have a frequency +0.2 tolerance of ±0.3%. The temperature stability of res- 0 onators is typically within ±0.3% over the range -20 to +80°C. Figure 4 shows temperature stability char- -0.2 acteristics for three types of resonators, a 480kHz PBRC-4.19A device and two 4.19MHz resonators, one with and one -0.4 4.19MHz ceramic resonator without built in load capacitors. -0.6

230°C ±5°C MAX -40-20 0 20 40 60 80 100 120 Temperature, °C 200°C SUGGESTED REFLOW PROFILE KBR-Y SERIES PBRC SERIES 150°C Frequency deviation 100°C Reference temperature = 25°C +0.6 1 HOUR BEFORE MEETING ALL +0.4 ELECTRICAL SPECS 60 SEC. 60 SEC. 20 SEC. GRADUAL COOLING +0.2 MAX 0 Figure 5. Recommended IR reflow profile — Surface mount resonators -0.2 PBRC-4.19B -0.4 4.19MHz ceramic resonator Surface Mount Process Considerations with built in load capacitor -0.6 The three types of resonators being discussed here were all specifically designed to be surface mounted and are capable of withstanding infra -40-20 0 20 40 60 80 100 120 red, convection and vapor phase reflow soldering Temperature, °C processes and subsequent circuit board cleaning. It is however recommended that exposure to the high temperatures involved during soldering be limited to Figure 4. Typical frequency vs. temperature characteristics a single time to prevent possible permanent damage for three types of surface mountable ceramic resonators. to the resonators. The recommended temperature profile for Infra red reflow soldering of the resonators is shown in Figure 5. KBR-Y Series PBRC-A/B Series The KBR-Y is a 2-terminal kHz band surface The PBRC-A/B resonators are leadless, ceramic mountable ceramic resonator. The frequency ranges bodies “chip” type devices. They consist of a ceramic currently available are: 380-430, 440-525, 600-655, substrate with solder terminals onto which a ceram- 795-815 and 960-1020 kHz. The gullwing type leads ic cover containing the resonator element, is her- have a spacing of 5mm in frequencies up to 655kHz metically sealed. The frequency range currently and 2.5mm in frequencies above this. Recommended covered by the PBRC-A series is 2.0 to 8.0 MHz and solder pad layouts for these two sizes of resonators for the PBRC-B series, 2.0 to 20.0 MHz is available. are shown in Figure 6. It is advisable to attach the The PBRC-B series has two load capacitors built plastic case of the resonator to the circuit board into the package and has three terminals on the using an adhesive which will cure during the reflow base. It is cycle to prevent stresses on the solder joints and otherwise identical in size and shape to the PBRC-A resonator caused by mechanical shock or vibration. series which has no internal load capacitors and thus is only a two-terminal device. Recommended land patterns for both types of resonators are shown in Figure 7. 2.4 2.4 Good solderability results should be obtained with a solder cream thickness of approximately 0.2mm. 1.5 1.5 1.4 1.4 Because these chip type resonators have no com- 6.5 3.9 pliant leads to absorb stresses induced by circuit 380-655kHz 795-1020kHz board flexing it is suggested that the placement of the resonator on the board be chosen such that Dimensions: mm stress be minimized. Experiments with a variety of thicknesses of paper/phenol and FR4 circuit boards Figure 6. KBR-Y solder land patterns with 2:1 aspect ratios have shown that alignment of the resonators with the short side of the circuit board allows in excess of twice the board flex before damage occurs to the resonator’s solder joints, com- pared to alignment with the long side of the board.

2.5 2.5 5.0

4.0 4.0

1.7 1.5 1.7 1.7 1.7 PBRC-B PBRC-A Dimensions: mm Figure 7. PBRC recommended land patterns

NOTICE: Specifications are subject to change without notice. Contact your nearest AVX Sales Office for the latest specifications. All statements, information and data given herein are believed to be accurate and reliable, but are presented without guarantee, warranty, or responsibility of any kind, expressed or implied. Statements or suggestions concerning possible use of our products are made without representation or warranty that any such use is free of patent infringement and are not recommendations to infringe any patent. The user should not assume that all safety measures are indicated or that other measures may not be required. Specifications are typical and may not apply to all applications. © AVX Corporation

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