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The purpose of this paper is to demonstrate laser microvia drilling of polyimide thin films from multiple sources before metallic sputtering. This process flow reduces Flexible Printed Circuit Board (FPCB) material, chemical and operational costs by 90 per cent in the construction of flexible circuits.

The UV laser percussion drilling of microvias in 25 μm thick polyimide films with low coefficients of thermal expansion (CTE) and elastic modulii was investigated. Results were obtained using Scanning Electron Microscopy and Surface Profilometry. Polyimide films tested included: Dupont™ Kapton^® EN; Kolon^® GP and LV; Apical^® NPI; and Taimide™ TA‐T.

There was no direct relationship between the top and bottom diameters and ablation depth rates between the polyimide films tested using the same test conditions. There was a direct relationship with exit diameters and etch rates at different laser pulse frequency rates and fluence levels. Laser pulse rates at 30 kHz produced 20 per cent larger exit diameters than at 70 kHz, however at 70 kHz the first pulse etched 16.5 per cent more material. High fluence levels etched more material but with a lower etch efficiency rate. Other microvia quality concerns such as surface swelling, membrane residues on the bottom side and surface debris inside the microvias were observed. Nanoscale powder‐like surface debris was observed on all samples in all test conditions.

This is the first comparison of material specifications and costs for films from multiple polyimide manufactures and laser microvia drilling. The paper also is the first to demonstrate results using a JDSU™ Lightwave Q302^® laser rail. The results provide the first insights into potential microvia membrane issues and debris characteristics.

The purpose of this paper is to prepare carbon fiber-reinforced polyimide matrix composites and to investigate the single role of carbon fiber in polyimide composites on tribological performance under distilled water condition.

Three carbon fiber-reinforced polyimide matrix composites were fabricated by using a hot press molding technique. The tribological behaviors of carbon fiber-reinforced polyimide matrix composites sliding against steel ball were evaluated with a ball-on-disk tribotester under distilled water condition. Meanwhile, the effect of different length of carbon fiber on the wear resistance of polyimide matrix composites was investigated during the sliding process.

The friction coefficients and specific wear rates of polyimide composites containing 100 μm carbon fibers were lower than those of other specimens. The wear mechanism of carbon fiber-reinforced composites was delamination under distilled water condition. The interfacial combination between the carbon fiber and matrix became worse with the increase of length of carbon fiber.

This paper reported the effect of the different length of carbon fiber on polyimide matrix composites to prepare mechanical parts in mining industrial fields.

For the drilling of polyimide multilayers with acrylic adhesives, more care must be taken than for epoxy glass material. Due to the different mechanical properties in the multilayer ‘sandwich’ of the polyimide and the acrylic adhesive layers, the drilling parameters require a higher level of control. To avoid defects in the hole, such as nail heading of the polyimide or an uncontrolled ‘rip‐out’ of the acrylic adhesive, the relation between the cutting speed of the drill and the feed needs to be adjusted for each drill diameter. The following guidelines are valid: Wider drill diameters require a lower rotational speed and a lower feed to avoid deformation of the polyimide in the hole. Smaller drill diameters need high rotational speeds and a higher feed to minimise smear. In general, the drilling performance of wider drills is better than that of smaller drills. In all cases, it was impossible to prevent smear of the acrylic adhesive in the multilayer holes. The only reliable method for removing acrylic smear is by plasma etching. The minimum etch‐back required for acrylic adhesive was found to be ≥6 µm, which would be equivalent to an etch‐back of only 2 µm of the polyimide film. To achieve the etch‐back rate, the time in the plasma chamber should be between 20 and 30 minutes at 90–110°C. After the etch‐back, a high pressure water rinse is needed to remove some residues in the hole prior to through‐plating.

The purpose of this paper is to discuss the fabrication technology and test of thermo-pneumatic actuator utilizing Si₃N₄-polyimide thin film membrane. Thin film polyimide membrane capped with Si₃N₄ thin layer is used as actuator membrane which is able to deform through thermal forces inside an isolated chamber. The fabricated membrane will be suitable for thermo-pneumatic-based membrane actuation for lab-on-chip application.

The actuator device consisting of a micro-heater, a Si-based micro-chamber and a heat-sensitive square-shaped membrane is fabricated using surface and bulk-micromachining process, with an additional adhesive bonding process. The polyimide membrane is capped with a thin silicon nitride layer that is fabricated by using etch stop technique and spin coating.

The deformation property of the membrane depend on the volumetric expansion of air particles in the heat chamber as a result of temperature increase generated from the micro-heater inside the chamber. Preliminary testing showed that the fabricated micro-heater has the capability to generate heat in the chamber with a temperature increase of 18.8 °C/min. Analysis on membrane deflection against temperature increase showed that heat-sensitive thin polyimide membrane can perform the deflection up to 65 μm for a temperature increase of 57°C.

The dual layer polyimide capped with Si₃N₄ was used as the membrane material. The nitride layer allowed the polyimide membrane for working at extreme heat condition. The process technique is simple implementing standard micro-electro-mechanical systems process.

A project has been undertaken to evaluate new sources of flexible circuit materials for use by the author's company. The vast majority of flexible circuits are fabricated from polyimide film and acrylic adhesive circuit materials. One new polyimide film has been evaluated as an alternative dielectric film. Thirteen suppliers of flexible circuit materials have been identified. The paper discusses the results of the mechanical and electrical properties evaluation study of some of the new sources of flexible circuit materials.

Polyimide nanocomposites were prepared with 0 and 1 wt% single wall-and double wall- CNTs (functionalized and non-functionalized) from BPADA and BAPP by refluxing in NMP. These nanocomposites were characterized using FT-IR, TGA, DSC, tensile strength, and Positron annihilation lifetime spectroscopy (PALS). The FT-IR spectra for all the samples showed the characteristic peaks of polyimide. TGA curves showed weight loss with temperature in two stages. The first stage 180-300 °C showed a weight loss of ~ 15% that may be associated with the release of trapped NMP. The second stage 500-750 °C with a drastic weight loss is associated with decomposition. The residual weight is ~ 40% at 750 °C for both pure polyimide and polyimide nano composites made with functionalized single or double wall CNTs. The non-functionalized CNT dispersed polyimide showed similar two-step behavior, but the weight loss is remarkably less and about 80% weight remained at 750 °C. DSC curves of all polyimide samples showed two distinguishable endothermic peaks at around 90 °C (the onset of NMP release) and 200 °C (structural change). PALS was used to study the nano-porosity. Positron lifetime has a correlation with tensile strength showing a decrease in tensile strength with increasing pore size in CNT-polyimide composites.

Due to their outstanding thermal stability, polyimides are now being carefully considered for use as matrix resins, adhesives, films and coatings. If successful, this unique class of polymers could greatly extend the present upper limit of 177°–205°C achievable in aerospace work with even higher temperatures and longer service life.

To establish an accurate and sensitive method to characterize the moisture content of a particular environment.

This paper proposes a relatively simple humidity sensor design consisting of electrodes on a suitable substrate coated with a polyimide material. The changes in relative humidity are denoted by a corresponding change in the polyimide material's electrical resistance profile. The design proposed in this work can be microfabricated and integrated with electronic circuitry. This sensor can be fabricated on alumina or silicon substrates. The electrode material can be made up of nickel, gold or aluminum and the thickness of the electrodes ranges typically between 0.2 and 0.3 μm. The sensor consists of an active sensing layer on top of a set of electrodes. The design of the electrodes can be configured for both resistive and capacitive sensing.

The polyimide material's ohmic resistance changes significantly with humidity variations. Changes in resistance as large as 4‐6 orders of magnitude are attainable over the entire operational humidity range.

As the sensitivity varies non‐linearly with the humidity, the measurement has to be carried out over a very wide range in order to calibrate the sensor. The sensitivity and output range of the sensor can be easily controlled by changing the electrode spacing or geometry.

The control of humidity is important in many applications ranging from bio‐medical to space exploration.

A simple, easy to fabricate and measure, and low cost resistive‐type humidity sensor was developed. The realized sensor is suitable for integrating with microfabrication. Hence, multiple sensors of varying sensitivities and output ranges could be integrated on the same chip. Over the last few years, newly emerging micro‐electro‐mechanical‐systems technology and micro‐fabrication techniques have gained popularity and importance in the miniaturization of a variety of sensors and actuators.

Polyimide deposition of thick layers (50‐60 μm after soft‐bake) is very important in the field of microelectronics; in particular for fabrication of microwave circuits for telecommunications, micromachining applications, MCM‐D and, in general, for pattern transfer. Spin coating is, even in this case, the only method that can provide good results in terms of quality, repeatability and reliability. This paper discusses problems concerning the polyimide deposition process for obtaining thick layers with an uniformity value within 10% and studying the process itself from a mathematical point of view. In particular, the thickness variation versus frequency has been analysed, checking the mathematical model in which the dependence is ω^−K(K=0.5). It is shown that the polyimide behaves differently depending on the residual solvents at the end of the process and that the model is verified only if the solvents are completely evaporated at the end of the process also. This resolves a certain confusion in the literature where the value of K changes from 0.5 to 1 with different justifications.

In this paper, we consider intrinsic properties of copper electrodeposited as plateup on polyimide substrate, thermal response of electrodeposited copper and fatigue performance of copper and copper/polyimide construction. The critical material characteristics examined are grain morphology and structure, crystallographic texture, microhardness, uniaxial strength and ductility and isothermal cyclic fatigue life. Given optimum processing conditions, copper plateup in flexible circuits displays fine grain structure, high ductility, adequate thermal stability, freedom from thermal embrittlement and excellent fatigue endurance over a wide range of strain amplitudes.