Microelectronic Bonding Processes Monitored by Integrated Sensors

Abstract

Real-time monitoring methods are beneficial for the control, optimization, and failure analysis of microelectronic packaging processes. The focus of this chapter is on the real-time monitoring of two widely used processes, soft solder die bonding and thermosonic ball bonding. The methods presented here use uniquely developed microsensors integrated on custom-made test chips using commercial double-metal CMOS processes.For the soft solder die bonding process, nine aluminum-based resistive temperature detectors were integrated on various locations on a test chip. The temperature was monitored during the placement of the test chip on the leadframe. The experimental results describe the wetting and spreading effects of the molten solder under the drip. Together with numerical results obtained with a transient thermal finite element model, the beginning of wetting can be quantified. For the soft solder PbSn10, wetting occurred around 30 ms after touch down. This method hence can be used to determine wetting times under different process conditions. The wetting time determines an upper limit of the throughput of the process.For the thermosonic ball bonding process, temperature and force sensors were integrated on test chips. The sensors are aluminum resistors and piezoresistive p + -and n + -diffused resistors placed around bond pads. A bond quality parameter can be derived from the temperature signal variation during bonding. The piezoresistive sensors permit the measurement of forces in the x-, y-, and z-directions simultaneously. The ultrasonic tangential force signal reached a typical value of 0.12 N on a 50 lm diameter contact zone and revealed significant process characteristics. Four process phases are identified which are necessary for a successful ball bond formation. These phases are assigned to initial stiction, sliding, bond growth, and deformation effects.

Measuring stress next to Au ball bond during high temperature aging

“…where Dr xx , Dr yy , Dr zz , and Ds xy are the changes of the stress tensor components averaged over the element location, p 11 = À3.8 Â 10 À10 Pa À1 and p 12 = 1.9 Â 10 À10 Pa À1 are typical values for the piezoresistive coefficients of n + -silicon [23,24], and u is the resistor angle with respect to the x-axis (Si crystal [1 1 0]-direction).…”

“…The mechanical stress changes are linked to a change of S by the formula for the relative resistance change [19,20,24] of a sensor element,…”

“…Test chips with integrated sensors have been used to obtain in situ information about thermal and mechanical effects including localized stress measurements on integrated circuits during or after packaging processes [18][19][20][21][22][23][24]. One of these integrated sensors [21] is presented here in a new application, providing signals of stress localized at a bonding pad.…”

Monitoring of thermo-mechanical stress via CMOS sensor array: Effects of warpage and tilt in flip chip thermo-compression bonding

“…Tools for measuring temperature and stress in-situ during wire bonding were demonstrated in [9][10][11][12][13][14][15][16]. These tools were developed and were comprised of piezoresistive and RTD elements to integrate force and temperature sensors via CMOS processes.…”

Synthesis and characterization of photosensitive methacrylates to give heat-resistant polymers

“…Among them, the polymers having acryloyloxy group (acrylate-type photopolymer [1][2][3][4][5][6][7][8]) surpassed the others in terms of the extent of utilizing fields and consumption, because of their advantages to form transparent, flexible, strong, and thick films. One of their uses is solder resist [9][10][11][12] in which the key structure is epoxyacrylate [13][14][15][16]. 'Epoxyacrylate' is an idiomatic expression and, precisely expressing, it should be referred to as epoxymethacrylate compound.…”