Smooth Copper Signal Integrity

The High Density Packaging (HDP) user group has completed a project evaluating the high frequency loss impacts of a variety of imaged core surface treatments (bond enhancement treatments, including chemical bonding and newer low etch alternative oxides) applied just prior to press lamination. Initial high frequency Dk/Df loss measurement results did not show a strong correlation with any of the methods utilized within this project to measured surface roughness. The more significant factor affecting the measured loss is the choice of pre-lamination surface treatment.  Most of the new chemical treatment systems outperform the older existing systems which depend upon surface roughness techniques to promote adhesion.

Project stage: 
Lead company: 

If you are interested in participating in this project:

Members - Go to the "Subscribe Here" section to the right and select the "Subscribe to space" key.

Non Members - Go to the "Contact" section to the right and select the "Contact project facilitator" key.

Idea Information


Signal Integrity as measured by insertion loss is becoming critical at higher frequency. The variation in insertion loss from a single design is becoming a concern for the OEM’s. Even dictating the foil, laminate and oxide treatment can result in variation in insertion loss from supplier to supplier. The foil can accounted for a 12% change in loss performance (shinny foil to HVLP), moisture can produce a loss performance of 6-8% (dry to fully hydrated) but the largest effect is innerlayer bonding methods (classic/alternative oxide treatments and other adhesion promoters) that can contribute up to a 50% change in loss performance.  (Paper from Merix at PCB West Sept 2011). The HDP User Group members requested that an evaluation of bonding chemistries/alternative oxides be undertaken to understand this variation.



Signal Integrity as measured by insertion loss is becoming critical at higher frequency. In addition to specifying the copper foil and electric characteristics of the laminate material to be used, the impact of oxide or other adhesion-promoting treatment prior to lamination may have a significant impact on loss at higher speeds.

 Until recently, most inner layer pre-lamination treatments roughened the copper surface using a combination of etching and oxidizing agents to promote interlaminar adhesion and product reliability

Alternative oxide treatments and newer chemical bond enhancement treatments were developed to eliminate pink ring and provide smoother copper for enhanced signal integrity

This project was undertaken to evaluate the high frequency loss impacts of a variety of these treatments

This project will look at 3 existing/ traditional and 3 new chemical treatments

SEM example of existing treatment

SEM example of new chemical treatment

Definition Information

Goals / Benefits: 



This project will look at the effect adhesion promoters have on the signal integrity properties.

This project will not focus on metrology and reliability issues concerning smooth copper.

This project will not be choosing the “best” adhesion promoter.

Benefits of Project:

The project will produce a written report that will provide the insertion loss data and variation in performance due to different adhesion promoters, which can be used to increase our members’ awareness of poor treatment choices for high speed applications.

This data will enable a better understanding of the best and worst case scenarios for modeling purposes.

High level objectives: 

Evaluate candidate Adhesion promoters based on Signal Integrity (insertion loss)

Create a Test Vehicle for Smooth Cu that can be used on future projects/phases

Correlate Cu roughness with SI properties if possible

Understand difference between roughness measurements techniques

Evaluate the Thermal Shock results of the candidate Adhesion Promoters

Evaluate a variety of inner layer pre-lamination surface copper treatments (six were selected)

Flatbond GT/GC, MEC

Secure HFz, Atotech

Multibond HF, MacDermid

Glicap, Shikoku

Bondfilm, Atotech

Cobra Bond, OMG (Baseline)

 Use three different surface roughness measurement techniques

  • White Light Interferometer
  • 3-D Laser Scanning Confocal Microscope
  • White Light Vertical Scanning Interferometer

 Use two different measurement techniques to evaluate signal integrity, specifically insertion loss:

  • SPP (no connector) coupon for 1 to 20 GHz measurements
  • Stripline coupon

Evaluate basic laminate reliability

  • Thermal shock coupon


Smooth Cu foil test vehicle for use in future evaluations of surface treatments

Final Report of Adhesion Promoter Results

Insertion Loss vs. Frequency

Return Loss vs. Frequency

Includes SI to roughness correlation if possible to analyze

Paper/Presentation for Conference



This project will build a set of test vehicles with various adhesion promoters/chemical treatments and test them for Signal Integrity/Insertion loss. The insertion loss will be evaluated by both SPP and S3 evaluation techniques. The surface treatments will also be thermal shocked to test for basic thermal reliability by a 6 x reflow cycle. Surface roughness will be measured by several non-contact techniques and evaluated against the Loss data to see if any correlation exists.

Key Participants: 
i3 Electronics
Isola Group
MacDermid Alpha
PWB Interconnect Solutions
RBP Chemical Technology
Rogers Corporation
TTM Technologies