TY - BOOK

T1 - Interfacial adhesion in printed circuit boards

AU - Nothdurft, Philipp

N1 - no embargo

PY - 2017

Y1 - 2017

N2 - The surface modification of copper foils by means of liquid phase reaction with different monomeric and polymeric molecules is investigated with focus on adhesion improvement of copper/FR-4 prepreg joints. The substrate preparation is based on common industrial methods to avoid oxidation of the copper surface prior to modification. Analysis and characterization of the surfaces after treatment were performed using various physico-chemical methods. The modified copper substrates were laminated to standard FR-4 materials as used in the manufacturing of printed circuit boards. From these samples the adhesion strength increase or decrease was measured in comparison to copper/prepreg samples with no introduced interlayer. The reliability of these specimens at temperatures up to 260 °C and high humidity levels (80 %) was evaluated by quality measurement procedures used in printed circuit board industry. An improvement of the interfacial adhesion was observed under special conditions and material combinations. However, the long term stability of the samples was not given when exposed to heat or high humidity. Various mechanisms are reported in literature, which can cause adhesion loss between copper and epoxy resins. Because of this, the focus in the second part of this work deals with determining the predominant failure mode for delamination. Delamination is a very complex phenomenon and depends on the characteristics of the prepreg system (e.g. curing agent, moisture absorbance,…), the copper surface (thickness of oxide layer, oxide species), and interactions when both are brought into contact. The performed experiments revealed no degradation of the FR-4 materials at temperatures achieved by reflow cycling. In addition, the humidity during prepreg storage had no influence on the adhesion strength. KPFM technique was implemented as new promising analysis tool for the characterization of cross section samples. SEM with integrated heat chamber was used to monitor in-situ changes at the interface during simulation of temperature cycles. The results obtained from surface modification and adhesion failure mode evaluations in combination with the knowledge gained from literature research lead one step further to the development of a new technology enhancing the adhesion strength of copper/epoxy joints based on chemical bonding.

AB - The surface modification of copper foils by means of liquid phase reaction with different monomeric and polymeric molecules is investigated with focus on adhesion improvement of copper/FR-4 prepreg joints. The substrate preparation is based on common industrial methods to avoid oxidation of the copper surface prior to modification. Analysis and characterization of the surfaces after treatment were performed using various physico-chemical methods. The modified copper substrates were laminated to standard FR-4 materials as used in the manufacturing of printed circuit boards. From these samples the adhesion strength increase or decrease was measured in comparison to copper/prepreg samples with no introduced interlayer. The reliability of these specimens at temperatures up to 260 °C and high humidity levels (80 %) was evaluated by quality measurement procedures used in printed circuit board industry. An improvement of the interfacial adhesion was observed under special conditions and material combinations. However, the long term stability of the samples was not given when exposed to heat or high humidity. Various mechanisms are reported in literature, which can cause adhesion loss between copper and epoxy resins. Because of this, the focus in the second part of this work deals with determining the predominant failure mode for delamination. Delamination is a very complex phenomenon and depends on the characteristics of the prepreg system (e.g. curing agent, moisture absorbance,…), the copper surface (thickness of oxide layer, oxide species), and interactions when both are brought into contact. The performed experiments revealed no degradation of the FR-4 materials at temperatures achieved by reflow cycling. In addition, the humidity during prepreg storage had no influence on the adhesion strength. KPFM technique was implemented as new promising analysis tool for the characterization of cross section samples. SEM with integrated heat chamber was used to monitor in-situ changes at the interface during simulation of temperature cycles. The results obtained from surface modification and adhesion failure mode evaluations in combination with the knowledge gained from literature research lead one step further to the development of a new technology enhancing the adhesion strength of copper/epoxy joints based on chemical bonding.

KW - Grenzflächen Adhäsion

KW - Leiterplattern

KW - FR-4 Materialien

KW - Oberflächenanalyse

KW - Stabilität

KW - Gründe für Delamination

KW - organische Grenzschichten

KW - Interfacial adhesion

KW - printed circuit boards

KW - FR-4 materials

KW - surface analysis

KW - reliability

KW - delamination failure modes

KW - organic interlayers

M3 - Doctoral Thesis

ER -