RF pool – insights and details

UPDATE 7 May 2014 : New options: materials I-Tera and RO4350B form the bases of the pooling service

Eurocircuits have been producing PCBs on RF materials for many years. At first we offered Rogers RO4000 series. More recently we have focussed on Isola’s I-Tera material. I-Tera offers significant cost-savings compared to the Rogers materials. This makes it a critical component in our drive to provide a low-cost solution for RF development using order pooling technology.

RF pool updated

Our RF customers have asked us two questions:

  1. Can Eurocircuits provide a low-cost solution for RF prototype and development PCBs?
  2. Can Eurocircuits offer standard materials and builds which we can use for our designs, rather than starting from scratch each time?

Over the last few months we have had extensive discussions with our customers and RF experts to find the best way to meet these requirements.

The answer is our updated RF pool service:

  • Isola’s I-Tera provides a lower-cost material but still with a high performance specification.
  • Order pooling, sharing production costs between a number of different orders on the same production panel, is the only way to cut process costs for prototype and development PCBs without sacrificing quality or delivery.
  • Order-pooling needs standard builds which enough customers will order to fill the production pooling panels.
  • The standard materials and builds, developed after wide-ranging sector consultation, make pooling possible but also help RF engineers complete their designs faster.

How can RF pool help you with your design?

Standard builds

We offer two materials in the pooling service to give a wider range of performance: Isola I-Tera and the somewhat more expensive Rogers RO4350B™.

Isola I-Tera is suitable for many of today’s high speed digital and RF/microwave applications. It has a dielectric constant of 3.38, stable between -55°C and +125°C up to 20 GHz. Tg is 200° and Td 360°. Its low dissipation factor (Df) of 0.0035 makes it a cost-effective alternative to PTFE and other commercial microwave and high-speed digital laminates.

Rogers RO4350B™ has a higher specification, making it an ideal material for broadband applications. It has excellent dimensional stability, including a Z-axis CTE comparable to that of copper. Tg is 280°.

Both materials have UL 94 V0 flammability certification.

Download the data sheet for I-Tera here and for Rogers RO4350B™ here.

For 4-layer boards we offer a standard build combining I-Tera or RO4350B™ with Isola PCL370HR high performance 180°Tg FR4 prepreg:

The next two pictures show the theoretical and the actual build-up of a 4-layer RF pool PCB.

Other specifications (1.55 mm thickness, 12 micron copper foil and 6-layer boards) are all available as non-poolable options (you need to order a full panel of these builds, rather than just a part of a standard pooling panel).

For 2-layer boards, RF pool offers the flexibility of two thicknesses of either I-Tera or RO4350B™ : 0.50 or 0.25 mm.

As we use standardised builds in RF pooling, we can provide the following tables for the impedance of a surface microstrip as a function of different track widths.

These are based on I-Tera using 35 micron outer layer finished copper thickness (18 micron foil plated up). For 4-layer boards the inner layer finished copper thickness remains at 18 microns as there is no plating up. However the inner layers are usually the reference layers in the impedance calculation for a surface microstrip, so their copper thickness is less important to the impedance calculation.

4 layer PCB with 0.254 mm core thickness

Impedance of Surface Microstrip

Track width (mm)

0.1

0.125

0.15

0.175

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

35 um
End Cu

106.92

100.28

94.55

89.53

85.04

77.31

70.8

65.17

60.22

55.8

51.8

48.16

44.81

2-layer PCB with 0.508 mm core thickness

Impedance of Surface Microstrip

Track width (mm)

0.1

0.125

0.15

0.175

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

35 um
End Cu

135.64

128.99

123.27

118.24

113.76

106.03

99.52

93.89

88.94

84.51

80.52

76.87

73.52

If you want to calculate the effect that the solder mask has on the circuit behaviour, we use SUN Chemicals XV501T-4 HV Semi Matt Clear Resist – CAWN 1331 green soldermask, dielectric constant of 3,9 – 4,0. Link to Sun Chemical

Special builds

Other materials (Rogers RO4003), other builds and other copper weights may be available as special builds. Use the “Launch inquiry” option in the price calculator, tick the “Special build” box and upload your data with a clear drawing showing what you require. Our engineers will evaluate your specification and report back whether we can build your board, and if so, what the price will be.