Qualification Report Polymer RF Filters - rfsworld.com · The Clear Choice in WirelessTM Polymer...

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RADIO FREQUENCY SYSTEMS

Radio Frequency Systems

Please visit us on the Internet at http://www.RFSworld.com

T h e C l e a r C h o i c e i n W i r e l e s s T M

Polymer Qualification Report October 2003

V3.1

Qualification Report of

Polymer RF Filters

UMTS Dual Tower Mounted Amplifier

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V3.1

Contents:

Page:

Abbreviations 3

General Description 4

Material Selection 5

Silver Plating Process 6

RF-Performance Test 6

Mechanical & Thermal Tests 8

Thermal Shock Test 8

Peeling Strength Test 9

Thermal Cycling & Humidity Test 9

Peak Power Test 10

Extended Heat Test 10

Continuous Power Test 11

Passive Intermodulation Test 11

Vibration, Shock & Bump Test 11

EMC- & Lightning Test 11

Summary 12

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V3.1

Abbreviations

Ag Silver C Degree Celsius

Cu Copper CTE Thermal Coefficient of Expansion DELTA Independent Certified Test Bureau dB Decibel EN European Standard/Norm ETSI European Telecommunications Standard Institute g Specific gravity (9.81 m/s2) GSM Global System for Mobile communication HDT Heat Deflection Temperature Hg Mercury Hz Hertz IEC International Electro technical Commission KHz Kilo Hertz kW Kilo Watt MHz Mega Hertz NWA Network Analyzer PEI Polyetherimide PIM Passive Intermodulation PVD Physical Vapor Deposition RH Relative Humidity RMS Root Mean Square SPS Syndiotactic Polystyrene TMA Tower Mount Amplifier Triplexer Three filters in one block / filter body.

UL Underwriters Laboratory UMTS Universal Mobile Telephone System W Watt

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V3.1

General Description

Looking on a permanent basis for new and innovative solutions in wireless communications, Radio Frequency Systems (RFS) has developed an air cavity filter made predominantly by polymeric materials. The world’s first polymer-based 3G filter has got better RF properties than its aluminium counterpart, although having just half the weight.

The R&D team of RFS has reshaped this innovative technology very thoroughly. After having successfully tested a four-cavity combiner filter in a preliminary project, it was decided to implement the technology in a Triplex filter for a new UMTS TMA.

This report will provide all detail information on the Polymer filter technology demonstrating through extensive testing in Materials selection, Plating process, Performance testing, the quality of the material used and its long-term durability even in the most difficult / harsh environment.

The following sections explain each step and process that RFS took during the testing period.

Figure 1: Left: Raw moulded UMTS filter Right: Silver-plated UMTS filter

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V3.1

Material Selection

The criteria for selecting the materials are concentrated on the mechanical properties and the thermal performance of the materials. Low thermal expansion (CTE) along with high melting point and low water absorption were among the key properties searched for.

After a number of tests, the materials selection was reduced to two alternatives with thermal expansion coefficient similar to aluminium.

Experiments were carried out in order to identify suitable types of screws for attaching top plates, connectors etc. The screw types that were selected, demonstrated excellent functionality. The effective torque available to generate the clamping force is at least as good as the current aluminium technology, with some better safety margin, and full assurance that the screws are durable.

Machining and drilling were demonstrated in these two materials without any difficulty.

Critical Materials Requirements for operation:

Upper limit of temperature > 140 C Thermal expansion < 25 x 10-6 /K Moisture absorption: No dimensional change (swelling) Flammability requirement: UL Approved Thermal conductivity: As high as possible

Critical Materials Requirements for Processing:

Shaping: Injection mouldable Freedom from porosities required Dimensional stability of process < 0.1 Achievable surface roughness < RA 3.2

Cu/Ag-Electro Plating with good adhesion Milling, drilling and tapping to be possible

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V3.1

Silver Plating Process

Two different methods of surface metallization were considered: Physical Vapour Deposition (PVD) and conventional chemical/galvanic plating.

Experiments showed that PVD was not a usable solution. This was partly due to incompatibility between the nature of the process and the geometries required for filters, and partly due to the poor adhesion of the deposited metals on the plastic surface. The plating process was then clearly defined thereof.

All further experiments were focused on conventional methods and a specific process was defined. The adhesion tests performed showed exceptionally good results – in fact better than conventional silver-plated aluminium filters.

RF-Performance Test

The following RF Tests were performed on the Cu/Ag-plated filter housings mounted with Ag-plated aluminium top plates and brass tuning screws:

Return Loss & Insertion Loss testing at temperature o T = 20 C, 30 C, 40 C, 50 C, 60 C

Temperature drift between +20 C and +60 C ( T=40 )

Return Loss & Insertion Loss testing at temperature o T = 10 C, 0 C, -10 C, -20 C, -30 C, -40 C

Temperature drift between -40 C and +20 C ( T=60 )

Similar test were performed with an identical milled aluminium filter and its temperature drift was measured to get a target value of acceptable drift related to filters in polymer materials.

This temperature drift is in fact a demonstration of thermal stability. Most materials shrink in low temperature and expand under high temperature. The lower the coefficient of thermal expansion (CTE) is, the smaller the temperature drifts.

The main difference between aluminium and polymeric material is that aluminium has got a uniform CTE of 23 x 10-6 m/ whereas glass fibres reinforced polymeric materials always have got a CTE value parallel to flow direction and another CTE value measured at cross flow direction. This is due to the orientation of the milled glass fibres in the granules.

The following plots recorded on an Agilent 8753 ES Network Analyser with the filter in a Sanyo Environmental Chamber MTH 4100 show the filters RF-performance.

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V3.1

The temperature drift is calculated to be 35 KHz/ c for the polymer filters compared to 36 KHz/ c for aluminium filters.

Figure 2: Temperature drift from 20 C to 60 C

Figure 3 Temperature drift between -40 C and +20 C

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V3.1

Mechanical & Thermal Test Requirements:

Several tests were carried out on these first polymeric material filters in order to validate the product quality & lifetime. The most important issues related to product quality is the adhesion of silver and the long-term performance after humidity and temperature cycling. (Dimensional stability). The tests were:

Thermal Shock test Peeling Strength Thermal Cycling (-30 to 85 C, total 500 hrs.) Humidity Test High Power & Peak Power Test Passive Intermodulation (PIM) test Shock, Vibration & Bumps Extended Heat Test (150 C, 1 hr) EMC & Lightning Test

Thermal shock test

This test gives a good indication of the silver adhesion to the filter body. The test is usually meant for silver plated aluminium and is described in DS Inf.14 as: ” The item was heated up to 200 C for 30 minutes thereafter the item is cooled rapidly in water. The item must not show any signs of blistering or loose silver flakes that can be peeled off.“ There were no sign of blisters and no sign of loose silver. The silver plating was exactly as good as before the test. This test, performed on a significantly large number of units, proves that the adhesion quality is the same standard and even better than the adhesion of silver to die-cast aluminium filters.

Fig.4: Three silver-plated UMTS TMA filters heated to 200 C for 30 minutes.

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V3.1

Peeling strength test

The minimum pull-off force was measured to 25 Newton or 2.5 Kg/cm2. The test was carried out on three individual filters as shown in Figure 5. It showed that 1 cm2

silver plate could actually carry a dual UMTS TMA made by Polymer RF filters.

Thermal cycling & Humidity Test (-30 C to 85 C & 85% RH)

The filter is placed in a climatic chamber (Sanyo Atmos chamber MTH-4100) and a temperature cycling is applied as described below:

STEP 01: 25 C 85 C, duration ¼ h STEP 02: 85 C, duration 1½ h STEP 03: 85 C

-30 C duration ½ h STEP 04: -30 C duration 1½ h STEP 05: -30 C 85 C, duration ½ h

The relative humidity is set to 85% - so the filter is in high humidity during the warm temperatures and iced during the temperatures below 0 C.

This test was conducted without interruption for 35 days – 840 hours in total.

The result of this visual inspection showed a few discoloured pinholes in the silver, as a result of high humidity. The filter was performing as before the test and therefore these minor spots were considered acceptable in view of the tough test. All solder joints were in perfect condition – no sign of cracks or any other defects.

This test is showing that a long lifetime can be expected. Most likely an even longer

lifetime than for die-cast aluminium can be expected due to the fact that there is no risk of migration from the base material through the copper/silver layer, which is the fact when the filter body material is metallic.

Figure 5: 1 cm2 copper soldered to the silver and peeling strength measured with dynamometer

Figure 6: Filter appearance after 35 days Temperature- & 85% RH Humidity-Test

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V3.1

Peak Power Test

Five polymeric filters were tested for power handling in order to find the peak power level and/or when the arcing would occur in an altitude test chamber. The power test conditions were as described below:

Test Frequency = 2110 MHz Test Power = 100 W at the TX port

The pressure was reduced until arcing occurs. Peak Power value is calculated as follows:

100 W x 2 x 34.6 = 6.920 W (34.6 is the altitude factor, Pressure 100 mm Hg)

No arcing was detected on any of the five UMTS Polymer filters, so max. Power level is stated to 100 W RMS and Peak Power 5 kW in the specification.

Extended Heat Test

Data from a polymer filter was kept in the Network analyser (Agilent 8753ES). Afterwards the filter was placed in a 150 C warm oven for 1 hour. The filter was connected to the Network analyser again and its performance was compared to the data collected before the heat test.

The filter remained within specification as regards return loss > 18 dB in both RX and TX when being 150 C warm, demonstrating that the polymer filters perform well, even outside the temperature extremes for aluminium filters.

Fig. 7: High power tests 2 x 30 W

Fig. 8: UMTS Polymer Filter placed in Termaks oven @ 150 C, Duration 1 hour

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V3.1

Continuous Power Test

In order to verify how the polymer filter is performing during continuous power input and to see the temperature raise due to the TX insertion loss (max 0.3 dB), a filter was hooked up to two RF Power amplifiers with 2 x 30 W input power on the TX-port. The duration of the test was 2 hours.

The temperature of the TX filter rose from 23 C to 29 C – consequently, the temperature difference was only 6 from ambient. This is due to the low insertion loss of 0.3 dB that corresponds to 3W dissipation from filter loss, showing that the filter is able to endure high power without risk of extreme temperature increase.

Passive Intermodulation Test

Passive Intermodulation (PIM) both reflected and transmitted was measured on 60 filters with input power of 2 x 20 W. The measured 7´th order PIM-level was better than -130 dBm. The specification states better than -115dBm. RFS is confident that the PIM specifications always will be met or exceeded with this technology.

Vibration, Shock & Bump Test

A certified independent test bureau performed these tests according to ETS 300 019-2-4, Environmental tests, Stationary at non-weather protected locations, Class 4M5

There were no external structural errors visible to the certified independent test bureau during or after vibrations and bumps. The unit was fully functional before and after the test. RFS DENMARK A/S was responsible for all the testing. A separate report is available on request.

EMC- & Lightning Test

The certified independent test bureau also carried out an EMC-Test on the DUAL UMTS TMA with polymeric filters. The tests performed were:

Electrostatic discharges according to:

EN 61000-4-2:1995+A1 IEC 61000-4-2:1995+A1

The product meets the following requirements of the standards:

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ETSI EN 301 489-1 V1.4.1: 2002 Electromagnetic compatibility and Radio spectrum Matters (ERM); Electro Magnetic Compatibility (EMC) standard for radio equipment and services; Part 1: Common technical requirements.

ETSI EN 301 489-8 V1.2.1: 2002 Electromagnetic compatibility and Radio spectrum Matters (ERM); ElectroMagnetic Compatibility (EMC) standard for radio equipment and services; Part 8: Specific conditions for GSM base stations.

A separate report is available on request.

Summary

RFS has gained an extensive expertise in polymer filter technology. The application of glass & fibre reinforced polymer material is suitable and even better than aluminium for filter houses used in coaxial air cavity filters.

Tests have demonstrated that:

Moulding and plating processes can be applied with very good results.

The product lifetime is likely to increase, as there is no risk of aluminium migration through the copper/silver-layer.

RF-power testing shows that 2 x 30 W CW input power at UMTS frequencies can be sustained.

Peak Power handling is measured up to 6.9 kW without arcing.

PIM was tested with 100% yield at a level better than 130 dBm.

Besides, it has major advantages:

A reduction by half the weight compared to aluminium filters

The suppression of the secondary machining and a dramatic increase of the lifetime of the mould (about 10 times).

Based on the testing of Polymer RF-Filters, it can be concluded that the Polymer filters perform as well or better than the aluminium filters in terms of the product performance, quality and lifetime.

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Qualification Report Polymer RF Filters - rfsworld.com · The Clear Choice in WirelessTM Polymer...

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Transcript of Qualification Report Polymer RF Filters - rfsworld.com · The Clear Choice in WirelessTM Polymer...