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Compare the conditions before comparing the numbers

An ITEQ Dk and Df comparison is useful only when the reported values describe sufficiently similar measurements. Dk describes permittivity; Df describes dielectric loss. Frequency, test method, resin content and specimen construction influence their interpretation. A lower number taken from a different measurement basis is not automatically a better material for the finished channel.

This page compares a small, documented set of official web-table records. It separates the 50% and 70% resin-content groups and withholds numerical ranking when the selected records cross those groups. Matching the visible labels is a necessary screening step, not proof that all unreported specimen details match. The result is a reference comparison, not a material-substitution approval.

For a searchable family directory and thermal-property filters, use ITEQ PCB materials. For a quotation against an approved construction, use ITEQ PCB manufacturing. The purpose here is narrower: help the engineer decide what the electrical numbers can and cannot support before choosing a model or revising a stackup.

Read the reference set with its group labels

All listed electrical values are reported at 10 GHz using IPC-TM-650 2.5.5.13. The table retains the resin-content group and shows the separate Tg method for context. The manufacturer鈥檚 summary pages do not fully describe the exact glass style, copper foil, conditioning and test specimen for every entry. Obtain the controlled construction data before using these numbers as a design input.

The , and are kept separate in the records. When a document is revised, update the source and relevant conditions together. Do not preserve an old property value under a new document label simply because the grade name did not change.

A condition-matched reference comparison

Choose two grades to view their recorded electrical conditions. Within the same resin-content group, the worksheet calculates B minus A for Dk and Df, plus the Df percentage change relative to A. Across groups it shows the source values and the condition mismatch, without generating a percentage ranking. It performs no interpolation or conversion between resin contents.

For IT-180A as A and IT-158 as B, the listed Df values are 0.017 and 0.018 in the 50% group. Their difference is 0.001. Relative to A, that is approximately 5.88%. This arithmetic does not say that a PCB channel made with B has 5.88% more insertion loss. The full channel contains conductor loss, transitions and possible reflections, and its dielectric field is associated with an actual construction.

The denominator matters. Reversing A and B changes the percentage reference, even though the absolute magnitude of the difference is unchanged. Keep the chosen baseline in a design-review note. A percentage without the baseline, frequency and method is easy to misuse in a purchasing comparison or a performance claim.

What Dk and Df describe in the design process

Dk affects field distribution, propagation and transmission-line impedance. For an ideal homogeneous medium, propagation delay per length scales with the square root of relative permittivity. A microstrip includes fields in more than one medium, so its effective permittivity depends on geometry as well as the substrate. A laminate reference cannot be inserted into every structure without considering how the solver defines its material model.

Df is a dimensionless loss tangent. It is one contributor to attenuation in a dielectric-filled interconnect. The contribution changes with frequency and the field distribution. A surface trace, a buried stripline, a via transition and a connector launch do not share one universal loss-per-inch multiplier. It is misleading to turn a data-sheet Df directly into a complete board insertion-loss guarantee.

Copper also matters. Finished shape, foil roughness, treatment and plating can change conductor loss and the geometry used by an impedance model. When comparing two laminate candidates, ask whether the copper construction is held constant. If one candidate uses a different foil, a measured channel difference cannot automatically be attributed entirely to the dielectric resin.

The PCB impedance page addresses geometry-based starting calculations and their limits. Use a suitable field solver and construction-specific material model for controlled work. Then agree the measurement method and coupon design with the fabricator. A calculation, a laminate test and a finished-board measurement answer related but different questions.

Frequency, resin content and method are separate axes

Frequency labels must be preserved. A 1 MHz material measurement does not become a 10 GHz value because the board carries a fast signal. Likewise, the signaling data rate is not automatically the material test frequency. Edge behavior, channel response and the analysis method determine the relevant frequency range. Request an appropriate frequency-dependent model when the analysis requires one.

Resin content is a mass fraction associated with the construction. Different glass and resin proportions can change the effective dielectric response. The tool does not assume that a 50% reference can be converted to 70% by a linear percentage formula. Such a conversion would need a justified mixture model and the relevant material properties, not simply two marketing numbers from different families.

The method identifies how a property was obtained. Different test fixtures and extraction procedures can produce values that serve different purposes. A process-control Dk and a design-oriented value can both be legitimate within their definitions. Keep the intended use visible. The correct question is which model and evidence apply to the specified line and construction, rather than which published number looks most favorable.

Temperature, moisture and conditioning can also matter. Their absence from a short web table is a limitation of the summary, not proof that they have no effect. Ask for the relevant test conditions or supplier guidance. If two data sets lack enough information for a defensible comparison, leave the uncertainty in the record instead of manufacturing an exact ranking.

An alternate-material review for a routed channel

Suppose a channel misses its loss target and the team proposes a lower-Df laminate. Start by recording the measured or modeled channel, length, stackup, foil and transitions. Identify whether the present loss estimate already includes conductor roughness and via behavior. Changing a dielectric property in a simplified model may be useful for sensitivity analysis, but it does not identify every practical cause of the failed channel.

Next, obtain the proposed material鈥檚 applicable construction data. Keep dielectric spacing and trace geometry controlled during the comparison, or explicitly document their changes. A candidate that needs a different available bondline may require a new trace width to maintain impedance. That new width can affect routing density and conductor loss, so the material and layout changes should be assessed together.

Use the ITEQ stackup assignment page to record the candidate layer sequence. It documents thickness and identities rather than solving the channel. Keep the electrical analysis with the drawing revision and define what the prototype coupon or board measurement will test. Approve the resulting construction, not merely a material name selected by the online comparison.

For cost comparison, ask for quotations against the same electrical and acceptance scope. A lower-loss option may involve different available constructions or procurement conditions; no universal surcharge follows from its Df. The manufacturing page provides a documented budget worksheet, while this page remains focused on whether the electrical comparison is meaningful.

Dk and Df comparison questions