This paper describes a diode-array pulsed spectrometer (DAPS) that performs flash photolysis studies with a time resolution of 10 ns and a spectral resolution of 2.4 nm over a 6OO-nm wavelength window in the range of 3 5~ 11 00 nm. It employs a 1024-element photodiode-array detector with high dynamic range and low noise. Laser-pumped fluorescent dye mixtures are used as a novel, stable light source which enable it to record spectra with a photolimited SIN ratio equivalent to 0.001 abs. units in a single shot. The measuring light distribution can be tailored so that a constant SIN ratio across a spectrum is attainable even in regions of high absorbance. Electrical artifacts from the actinic laser or other discharges do not interfere with the measurement and the effects of scattered actinic light and fluorescence from the sample are minimized. The instrument is simple to build, using mainly standard lab equipment, and easy to maintain and operate.
In industrial practice, frequencies from 40 kHz up to 160 kHz are currently employed for wire-bonding while for experimental purposes, lower and higher frequencies from around 25 kHz up to 300 kHz are discussed. Typically, heavy aluminium wire or ribbon is preferably bonded at lower frequencies between 40 and 80 kHz, while thin aluminium or gold wires are wedge- or ball-bonded at frequencies between 100 and 140 kHz. We present a discussion of the pros and cons of different ultrasonic frequencies by looking at the mechanics during the bonding process. Higher frequencies allow shorter bonding times and permit bonding on more sensitive surfaces, but suffer from a narrower parameter window. This is mainly due to the smaller vibration amplitudes at the tool tip which can be employed for higher frequencies. The major benefit for many applications is that higher bond quality is possible even at lower wire deformation which additionally creates a healthier bond heel. Lower frequencies, on the other hand, seem to have advantages for rougher surfaces where some planarizing and smoothing is required before bonding can begin to take place, while running a higher risk of damaging the bond after forming it. Resonance effects can seriously damage bond formation, and ways are discussed on how to deal with this problem.
In hybrid electronics, it is a standard practice to perform 100% wire bond pull testing to ensure robust wire bonding of the components. The principle behind Mil-STD-883 method 2023.5 compliant wire bond pull testing is to position the hook underneath the wire and either pull until the wire breaks or, alternatively, pull to a predefined force. With high density layouts, small component geometry or staggered wire bonds, it has been a challenge for manufacturing operations to maintain consistency in “manually” placing the wirepull hook on wires with varying height, looping profiles and wire distances. The influence of loop height and wire distance is a significant factor in determining the true wire pull strength. A low wire loop will result in lower measured pull strength, while a higher loop will result in higher pull strength. Therefore, if we can accurately quantify the loop height and profile then we can place the wirepull hook in the optimum position for pulling. In this study we will demonstrate how the “parallelogram of forces” can affect wirepull measurements. With the advent of the current generation of automated wirebond pull testers, we can accurately determine the appropriate correction factor(s) for varying loop heights in order to position the wirepull hook at the precise location necessary for accurate and meaningful results. In addition, with real time yield monitoring, the new pull testers are capable of locating and identifying missing wires that can often be attributed to the high density of today's circuit designs.
F&K Delvotec Austria, located in Braunau, is a member of the F&K Delvotec group and focuses on bonding and testing equipment for small-scale production of high--quality electronic and semiconductor parts. The second business area concerns itself with developing and adapting bonding processes for new or unusual applications in the industry, such as bonding non-standard wire materials on non-standard surfaces, such as copper ribbon to reinforce the current-carrying capability of pc-boards.
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