MWJ Webinar Al Horn 032615 Rogers PIM Testing FINAL 032515 Rev1

PIM Testing at

Rogers Corporation

Advanced Circuit Materials Division

Patricia LaFrance, Chris Caisse, & Allen F. Horn, III

Lurie R&D Center, Rogers, CT

John Coonrod, Ling Smith, & Art Aguayo

Rogers Advanced Circuit Materials Division, Chandler, AZ

Evan Yuan & Sharon Young

Rogers Suzhou & Shanghai, China

1

Discussion Outline

What is PIM?

PIM standard at IEC

Reverse vs. Forward PIM

Description of Rogers laminate PIM tests

PIM Test Repeatability & Statistics

PIM Processing Observations and Experiment

Conclusions

2

Intermodulation (IM)

In a ideal linear system (where V = IR perfectly) no new frequencies can be generated. If f1 and f2 are input,

then only f1 and f2 will be output.

If a system is non-linear (like a power amplifier nearing its saturation point) then IM products can be generated

at frequencies such as (f1 - f2), (2f1 - f2), (3f1 - f2), (3f1 -

2f2), (4f1 - f2), (4f1 - 2f2), (4f1 - 3f2)..

Only some odd IM products will occur in-band:

IM3: (2f1 - f2)

IM5: (3f1 - 2f2)

IM7: (4f1 - 3f2)

3

Intermodulation (IM)

4

Passive Intermodulation (PIM)

PIM is IM generated by a passive system or device, such as a filter, power divider or antenna.

Power levels are extremely low. Even a very bad PIM level of -133 dBc (referenced to 20 watts) is 10-12 W.

Typical sources of non-linearity:

Nearby ferrous metals

Metal particles on a planar circuit

Metal particles in connectors

Corroded connections

Stressed connectors

5

PIM is not a basic material property

Like insertion loss, antenna efficiency, gain, return loss, and many other important electronic performance

measures, PIM is a property of a circuit or system, not of

a material. It also depends on input power and

frequency.

However, there are material properties such as copper profile that when properly controlled, can result in

consistently lower PIM.

We build a certain Rogers internal standard circuit and test it at standard conditions to assess the relative PIM

performance of different laminate materials.

6

PIM is not a basic material property

3rd order PIM is always highest in power, so if you measure a value for IM3, you can be certain that IM5

and IM7 will be lower power.

IM3 depends on 3rd power of the current density.

Different circuit designs will exhibit very different PIM values, even with the same material and connectors.

Example:

Rogers 50 ohm TL PIM circuit on 0.75 mm thick RO4730JXR laminate exhibits a PIM of about -153 dBc.

A customer builds a filter on this laminate that exhibits PIM of -168 dBc

7

PIM Testing at Rogers Standards Development

PIM Test Methods are addressed by the IEC TC46 WG6 Document IEC 62037.

IEC 62037 does not address testing of copper clad laminate materials

In general, IEC recommends testing Reverse PIM when possible.

Rogers presently tests for PIM using a method recommended by Summitek Instruments now Kaelus.

8

Reverse vs. Forward PIM Measurements

If PIM is relatively high (e.g., -130 to 140 dBc) and emanates from multiple point sources, the reverse PIM

measurement can result in cancellation, while the

forward measurement does not.

For low PIM and/or distributed sources, this is not an issue.

Both Kaelus and IEC recommend measuring reverse PIM when possible due to difficulties with the low power

PIM signal and the high power base signals incident on

the duplexer in the forward measurement.

9

PIM Testing at Rogers Method 2001 to present

Rogers PIM Test Method:

300 mm long 50 ohm microstrip transmission lines on 1.5 mm laminate, stiffened by lamination to 1.5 mm FR4.

DIN 7/16 coax to microstrip connectors soldered to each end

Port 2 of the test sample is connected to a low-PIM load.

43 dBm (20W),two-tone, swept, reflected measurements with Summitek SI-1900b instrument at

1900 MHz

10

PIM Testing at Rogers Method

Rogers PIM Test Method - continued

Manipulate sample and connectors to get best stable PIM value over the swept frequency

range (1930-1990 MHz)

Report average PIM value at 1870 MHz of the up and down sweeps in dBc.

dBm = dBc + 43

PIM tester performance is checked before and after each test session with a PIM source

and a low PIM load

11

Summitek 1900b PIM Tester

12

DIN 7/16 Connector

13

Next generation on PIM Testing at Rogers

DIN 7/16 currently used for many connections in a BTS system, but most coax to microstrip connections are now

made through low PIM solder-plated braided jacket cable

and simple coax to microstrip connector.

Due to the very large growth in telecom industry since 2001 PIM testing equipment is much more widely used,

more user-friendly and less expensive

Rogers has added PIM testing capability at our Suzhou and Chandler locations, with Kaelus iQA-1921c PIM

analyzers.

14

Next generation on PIM Testing at Rogers

1.5 mm thick 50 ohm TL circuits with 0.141 flexible solder plated low PIM cables and light weight Coax-to-

microstrip soldered connectors.

We measure PIM versus time at 1870 MHz generated by fixed 1990 MHz and 1930 MHz tones and manipulate

connections and stress to get best PIM levels.

We have shown we get same values on all three (two new iQA-1921cs and our Summitek 1900B)

15

Kaelus iQA-1921c PIM Tester

16

New PIM test set up

17

Soldered connection from 0.141 low PIM cable

18

Rogers Reporting of PIM Testing

Material Sample #

Best PIM

IM3

dow

n

Best PIM

IM3

up

Average

up&dow

n

Best PIM

IM3

dow

n

Best PIM

IM3

up

Average

up&down

Grand

AVG

DH2

Lot X08924

w/ 1 oz.

LoPro

1 -154.9 -154.6 -154.8 -146.2 -146.7 -158.2

2 -166.4 -166.6 -166.5 -154.9 -154.2 -154.6

3 -155.9 -155.9 -155.9 -160.3 -160.9 -160.6

4 -159.3 -159.6 -159.5 -155.6 -155.5 -155.6

DJ1

Lot X08922

w/ 1 oz.

LoPro

5 -156.4 -156.2 -156.3 -153.5 -153.6 -153.6 -158.4

6 -160.2 -160.4 -160.3 -163.1 -162.1 -162.6

7 -160.1 -160.3 -160.2 -155.5 -155.9 -155.7

8 -159.8 -159.4 -159.6 -159.3 -158.8 -159.1

19

PIM Testing at Rogers General results

Weve purposely obtained a wide range of data: (-105 dBc to 175 dBc), with high profile foils, added ferrous metals, and conductive particles

to help understand the test.

As long as the cladding is pure copper and nothing is added to increase PIM, the major

controlling variable related to a laminate is foil

roughness.

20

Laminate PIM versus Copper foil Profile

(Rq - RMS profile - microns)

-170

-160

-150

-140

-130

-120

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Rq - RMS Profile - (microns)

PIM

(d

Bc

)

21

Repeatability of PIM Test

Major concern is test repeatability

Repeatability of a PIM test is about 3 dBc, without disconnecting sample.

This is consistent with what Kaelus specifies for repeatability of their PIM sources.

22

Repeatability of PIM Test

Based on four sample measurements, the repeatability of a laminate PIM test is about 6 dBc, including dis- and re-" connection when measuring in the -155 to -170 dBc range.

Repeated samples/measurements are necessary to understand material performance.

23

PIM Statistics

The repeatability of measurements affected by normal random variation improves by a factor of

1/n where n is the number of measurements.

We have shown that the 95% confidence limit of a single PIM measurement is +/- 12 dBc.

By measuring groups of 4 samples we improve the 95% confidence limit to +/- 6 dBc.

More samples would reduce confidence limit e.g., sets of 8 samples would be +/- 3 dBc

25

PIM Statistics

With a 95% confidence limit of +/6 dBc for the groups of four samples, significant

measurement-induced variation is more common than you might think.

As the following Monte Carlo simulation demonstrates, if a group of four circuits is

measured on consecutive days and the results

compared, the most likely outcome is that one of

the days measurements has higher PIM by 3 dBc or more

26

PIM Statistics

The Monte Carlo method is so-named since it is simulates a real gambling session.

Randomly select a group of 1000 values that fit distribution of mean of -157 and sigma of 3 (this is the

first measurement).

Repeat random number generation for second experiment.

If you average the differences between measurement 1 and measurement 2, it will be close to 0.

However, if you look at the absolute value of the differences, result is quite different.

27

PIM Statistics

Trial Number "Run 1" "Run 2" Difference

Absolute

Difference

990 -159.2 -154.3 4.92 4.9

991 -154.9 -149.0 5.86 5.9

992 -159.4 -156.3 3.08 3.1

993 -151.8 -156.1 -4.26 4.3

994 -157.5 -156.6 0.90 0.9

995 -157.7 -154.6 3.05 3.1

996 -155.3 -157.6 -2.33 2.3

997 -155.5 -151.4 4.12 4.1

998 -156.4 -152.6 3.80 3.8

999 -159.1 -153.9 5.21 5.2

1000 -160.8 -153.4 7.43 7.4

AVG -156.97 -157.05 -0.08 3.35

Std. D. 2.91 3.05

Last 10 Lines & Averages for PIM Statistic Simulation

28

PIM Statistics

29

PIM Statistics Conclusion:

If you really want to understand moderate PIM differences, many measurements

must be made.

30

PIM Testing for Production Control

With purchase of new PIM testing equipment, we are starting to regularly measure PIM as a

production reference test.

31

PIM & PROCESSING

OBSERVATIONS

32

PIM & Processing Observations

Due to the large measurement 95% confidence limit of +/- 6 dBc, it is very time consuming to

collect significantly significant data comparing

effect of various factors on PIM.

Nonetheless, over the years, some things seem to be significant.

33

Material & Connector Stress

Stress in the material, connector, and solder joint can have a large effect on PIM.

We manipulate the sample and joints during testing to obtain the lowest PIM values

34

PIM, current density, power level and thickness

The PIM values depend highly on the current density on the conductors, with higher density

leading to higher PIM.

Standard input power level for many test protocols (including Rogers) is 20 W (43 dBm)

on a 50 ohm transmission line on 1.5 mm

laminates.

Circuits that have a lower current density will exhibit lower PIM than the value on this test

circuit.

35


Example:

A 50 ohm transmission line on 0.75mm RO4730JXR laminate exhibits PIM of about -150 to -155 dBc with two 20 watt tones at 1870

MHz.

A customer routinely builds filters on 0.75 mm RO4730JXR laminate that exhibit < -168 dBc with

two 20 watt tones at 1870 MHz.

36


Example:

A 300mm long 50 ohm transmission line on 1.5 mm RO4730JXR laminate can typically exhibit a PIM value of -163 dBc.

A 300mm long 50 ohm transmission line on 0.75 mm RO4730JXR laminate can typically exhibit a

PIM value of -150 to -155 dBc.

37


RO4350B laminate with standard foil is a non-antenna grade that uses a high profile copper foil

and exhibits high PIM in our standard test.

However, RO4350B laminates can exhibit low PIM at lower power levels.

38

Material 20 W 10W 5W 2W 1W

0.060" RO4350B Std Foil -145/-102 - - - -

0.030" RO4350B Std Foil -133/-90 -137/-107 -144/-107 -147/-114 -151/-121

0.020" RO4350B Std Foil -135/-92 -138/-108 -137/-100 -145/-112 -152/-122

PIM Levels with two tone inputs at power level listed below (dBc/dBm)

PIM & Processing observations

As an experiment we also added small amounts of Fe powder (~1%) to the 0.08 mm thick dielectric layer in the

center of a 1.5 mm laminate.

Dk & Df were not affected.

However, PIM was -120 dBc

Without added Fe, PIM would have been


Metallic powder on dielectric surface causes very bad PIM.

Years ago, a colleague was going to show me how removing Cu oxide would improve PIM.

As soon as he touched the surface with sandpaper and generated Cu particles, there

was a large increase in PIM.

40


We routinely use sanding to generate a range of bad PIM materials for our gauge analyses.

Start with a better than -160 dBc material.

Sand it a little to increase PIM to -143 dBc

Sand it more to increase PIM to -125 dBc.

Wipe the surface with a solvent-soaked rag to remove the copper particles and one can see

the PIM improve significantly

41


Similarly if a sample is under-etched and nodules of copper are left in the dielectric, you

would expect to see bad PIM.

Customers have told us that this happens.

However, Rogers has not been able to recreate the effect in a controlled manner.

42

PIM & Etching Residue

Etching Residue on Surface causes poor PIM We had installed a new etcher at R&D. Rinse section was not

functioning properly. Coupons exhibited poor PIM.

After the initial testing, the PIM coupons were cleaned by wiping with 10% sulfuric acid and rinsed with DI water.

Significant improvement in PIM was seen.

43

PIM improvement with solder mask and immersion Sn

Samples are 300 mm 50 ohm TLs on 0.75 mm laminates:

RO4534 Lot A bare Cu PIM = -144 dBc

RO4534 Lot A SM & immersion Sn PIM = -158 dBc

RO4534 Lot B bare Cu PIM = -150 dBc

RO4534 Lot B SM & immersion Sn PIM = -156 dBc

RO4730JXR bare Cu PIM = -154 dBc

RO4730JXR SM & immersion Sn PIM = -159 dBc

44


Customers report that ENIG results in poor PIM.

45

PIM Processing Experiment

We set up an systematic experiment to determine the effects of various processing changes on PIM.

These included:

Slight under etch

Cupric chloride & ammoniacal etching chemistry

Combinations of solder mask, bare Cu, and tin plating

Plating finish

HASL, immersion silver and tin

Surface cleaning

Microetch vs. pumice scrub

46

PIM Processing Experiment

We were hoping that many of the factors that had lead to improvements in PIM in the past

would be consistently demonstrated.

Unfortunately, the control circuits of 50 ohm TLs on 1.5 mm RO4730JXR laminate exhibit PIM of better than -160 dBc, so nothing could be

consistently better.

None of the factors we investigated showed a significant difference.

47

Conclusions

PIM is not a material property. It is a circuit and system property that depends on many variables.

Due to the high variability of PIM when testing near the noise floor, multiple samples are required to differentiate

between relatively low PIM materials.

Laminate copper profile is a major variable affecting the PIM of microstrip transmission lines.

Rogers is committed to monitoring PIM performance of our antenna grade materials.

48

Rogers Low PIM PTFE Materials

Since copper roughness is normally the major variable, Rogers PTFE-based materials with low

profile rolled foil have always exhibited low PIM

values.

RO3003, RO3203 and RO3035 laminates are silica filled for low z-axis CTE, very low

temperature coefficient of dielectric constant,

and relatively high thermal conductivity.

49

Antenna Materials: PTFE based

Dk

10 GHz

Df

10 GHz

Thermal Conductivity

(W/m/K)

PIM

(dBc)

RT/duroid5880

Laminates

2.2 .04 0.0009 0.26

Rogers Low PIM RO4000 Thermoset Materials

The use of LoPro reverse-treated foil has allowed the development of a family of low PIM

RO4000 laminates.

RO4500 and RO4700 antenna grade laminates exhibit the rigidity, low CTE, low

TCDK, and low cost circuit processing that

typifies all RO4000 laminates.

51

RO4000 Antenna Materials

Dk

10 GHz

Df

(2.5/10)

GHz


(W/m/K)

PIM

(dBc)

typical

RO4533

Laminates

3.3

0.0020

0.0025

> 0.60 0.60 0.60

UL 94V0

0.40 0.40

Arlon low PIM AD WG-PTFE-ceramic laminates

In January, 2015, Rogers finalized the acquisition of Arlon, LLC.

Arlons woven glass-PTFE-ceramic filled laminates are widely used in telecom antenna

applications requiring low PIM.

The AD-C series is priced for high volume applications

53

Arlon low PIM AD WG-PTFE-ceramic laminates

Dk

10 GHz

Df

10 GHz


(W/m/K)

PIM

(dBc)

AD250C

Laminates

2.50 .05 0.0014 0.30

The information contained in this presentation is intended to assist you in designing with Rogers products. It is not intended to and does not create any warranties, express or implied, including any warranty of merchantability or fitness for a particular purpose or that the results shown on the design guide will be achieved by a user for a particular

purpose. The user should determine the suitability of Rogers products for each application.

RO4500, LoPro, RO3003, RO3203, RO3035, RO4534, RO4533, RO4535, RO4350B, RO4730JXR, RO4725JXR, RO4000, RT/duroid, The world runs better with Rogers.,

and the Rogers logo are licensed trademarks of Rogers Corporation.

Copyright 2015 Rogers Corporation. All Rights Reserved.

55

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MWJ Webinar Al Horn 032615 Rogers PIM Testing FINAL 032515 Rev1