Maija Hoikkanen

Metal–Plastic Adhesion in Injection-Molded Hybrids

Polymer–metal hybrids are replacing steel structures in many applications. Combining metals and plastics is, however, complicated because they have very different physical and chemical characteristics. This study characterizes plastic–metal adhesion in insert-injection-molded hybrids. Diaminofunctional silane was used as a coupling agent between thermoplastic urethane and stainless steel. Before silane treatment, various surface treatments, including electrolytic polishing and different oxidation treatments, were applied to the steel inserts to understand better the bonding between silane and steel. The effects of the surface treatments and silane application on plastic–metal adhesion were studied by means of contact angle measurements, adhesion tests, and microscopic characterizations. Electrolytic polishing and oxidation of the steel inserts significantly improved the silane bonding to the steel insert, and consequently the plastic adhesion to steel.

The Effect of Bonding Temperature and Curing Time on Peel Strength of Anisotropically Conductive Film Flex-On-Board Samples

Today, flex-on-board (FOB) attachments are commonly used in a variety of applications. By using anisotropically conductive adhesives (ACAs), low-cost flex materials that could not withstand typical soldering temperatures can be utilized. This paper examines the effect of manufacturing process parameters on the peel strength of a FOB assembly with an ACA attachment. The effects of bonding time and temperature on the curing properties of the ACA were also studied. The mechanical strength of the assembly was studied using a 90° peel strength test. The results showed that, by elevating curing temperature, better peel test results were obtained due to the higher degree of cure of the ACA. Additionally, longer curing time increased the peel strength. However, it also caused a considerably higher deviation in the results. Failure analysis using scanning electron microscopy showed that, with a higher degree of curing, the failure location in the peel strength test changed from the flex-adhesive interface toward the adhesive-substrate interface.

Effect of Multiwalled Carbon Nanotubes on the Properties of EPDM/NBR Dissimilar Elastomer Blends

In the presence of multiwalled carbon nanotubes (MWCNT), polar nitrile-butadiene rubber (NBR) and nonpolar ethylene propylene diene rubber (EPDM) blends were prepared following a melt mixing method. For the preparation of MWCNT filled EPDM/NBR blends, two mixing methods were used: direct mixing and the masterbatch dilution method. Various physical, mechanical, and morphological properties are explored to elucidate the dispersion behavior of MWCNTs. It was concluded that the preparation method influences the dispersion of the nanotubes in different rubber phases and the properties of these blends are controlled by the degree of dispersion of the nanotubes in the two phases. GRAPHICAL ABSTRACT

High-Temperature Storage Testing of ACF Attached Sensor Structures

Several electronic applications must withstand elevated temperatures during their lifetime. Materials and packages for use in high temperatures have been designed, but they are often very expensive, have limited compatibility with materials, structures, and processing techniques, and are less readily available than traditional materials. Thus, there is an increasing interest in using low-cost polymer materials in high temperature applications. This paper studies the performance and reliability of sensor structures attached with anisotropically conductive adhesive film (ACF) on two different organic printed circuit board (PCB) materials: FR-4 and Rogers. The test samples were aged at 200 °C and 240 °C and monitored electrically during the test. Material characterization techniques were also used to analyze the behavior of the materials. Rogers PCB was observed to be more stable at high temperatures in spite of degradation observed, especially during the first 120 h of aging. The electrical reliability was very good with Rogers. At 200 °C, the failures occurred after 2000 h of testing, and even at 240 °C the interconnections were functional for 400 h. The study indicates that, even though these ACFs were not designed for use in high temperatures, with stable PCB material they are promising interconnection materials at elevated temperatures, especially at 200 °C. However, the fragility of the structure due to material degradation may cause reliability problems in long-term high temperature exposure.

Evaluation of mechanical and dynamic mechanical properties of multiwalled carbon nanotube-based ethylene–propylene copolymer composites mixed by masterbatch dilution

A two-step masterbatch mixing technique was studied for preparation of carbon nanotube-filled ethylene–propylene diene elastomer compounds, and compared to conventional one-step mixing process. In the two-step process, a masterbatch compound with carbon nanotube content of 50 parts per hundred was prepared by melt-mixing ethylene–propylene diene elastomer. This material was then compounded with pristine ethylene–propylene diene elastomer and composites with different carbon nanotube concentrations were compared. The aim of this study is to compare the efficiency of two different mixing processes on the dispersion of carbon nanotubes and to facilitate the handling of carbon nanotubes, as the masterbatch can be prepared in a controlled way and used for further dilution without the problems related to carbon nanotube processing. The compound properties were studied with emphasis on mechanical characterization and dynamic mechanical thermal analysis. Masterbatch mixing resulted in the similar mechanical properties of the composites compared to the direct mixing method. At the relatively low loadings of carbon nanotubes, the considerable improvements of the mechanical properties were observed. The aspect ratio of the carbon nanotubes determined by transmission electron microscope was found to be similar to the one calculated from the Guth equation. It showed a considerable reduction in aspect ratio independent of the used mixing method.