Smooth Copper Signal Integrity
This project is evaluating the effects of adhesion promoters when applied to initially smooth copper. The project objective is to understand the effect on signal integrity, as measured by insertion loss due to the variation of surface roughness caused by these oxide chemistry/adhesion promoters. The project will electrically measure the insertion loss of several commonly used adhesion-promoting treatments and measure and correlate the copper surface roughness after each treatment.
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.
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
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.
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
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.