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Semi-Additive Process for High Frequency Signal Substrates
Semi-Additive Process for High Frequency Signal Substrates
A new SAP process for low loss build-up materials with low desmear roughness and excellent adhesion at various processing conditions is covered.
Materials Tech

Materials Tech programs cover topics including:
Adhesives, Chemicals, Cleaning Solutions, Coatings, Components, Design, Embedded Technology, Fasteners, Finishes, Flex Circuits, Flip Chip, Fluxes, PC Fab, Solders, Solder Masks, Solder Paste and more.
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Authored By:
Fei Peng, Roger Bernards, Bill Decesare
MacDermidEnthone Electronics Solutions, USA

Naomi Ando
MacDermidEnthone Electronics Solutions, Japan

Summary
Higher functionality, higher performance and higher reliability with smaller real estate are the mantras of any electronic device and the future guarantees more of the same. In order to achieve the requirements of these devices, designs must incorporate fine line and via pitch while maintain good circuitry adhesion at a smooth plating-resin interface to improve signal integrity. The Semi-Additive Process (SAP) is a production-proven method used on low dielectric loss tangent (Df) build-up materials that enables the manufacture of ultra-fine circuitry.

The standard SAP process utilizes some roughening or texturing of the dielectric substrate in order to achieve sufficient adhesion; however, the rough surface at the plating-resin interface potentially increases transmission loss at high signal speeds. To promote signal integrity at high-frequency signal transmission, the next SAP process should provide high plating-resin adhesion as well as very smooth interface in between.

The next build-up material in demand should present high thermal and dimension stability, good chemical resistance to survive many cure and reflow processes in circuitry manufacture. It should also deliver excellent electric properties including high insulation reliability, low Df and low dielectric constant (Dk) to guarantee good signal integrity in high frequency signal transmission. Meanwhile, the good properties above bring challenges to the SAP process.

This paper will discuss a new SAP process for low loss build-up materials with low desmear roughness (Ra= 40-100 nm) and excellent adhesion (610-680gf/cm) at various processing conditions. Along with the process flow, the current work will also present results and a discussion regarding characterization on the morphology and composition of resin and/or metal plating surfaces using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), surface roughness analysis, plating-resin adhesion evaluation from 90o peel tests.

Conclusions
The new SAP-RIGID process combines innovative etching, conditioning and direct metallization techniques from the company. It contains similar processesas traditional SAP, which makes it adaptable to existing equipment sets. Moreover, the processed dielectric surface can maintain low surface roughness as well as supports superior dielectric-plating adhesion through chemical bonding. The SAP-RIGID process has been successfully applied to an epoxy and/or cyanate ester type dielectric materials MATERIAL A and achieved very low desmear roughness (Ra= 80 plus/minus 18 nm) and excellent adhesion (658 plus/minus 18 gf/cm) on it. Considering the general lower limit for the dielectric-plating adhesion on MATERIAL A (550 gf/cm), the application of the current SAP-RIGID is a typical 6-sigma capable process both in short-term (Cpk= 2.51) and long-term (Ppk= 2.06). In addition, SAP-RIGID also opens good potential on other dielectric materials widely used in the current SAP market.

Initially Published in the IPC Proceedings

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