Modeling vapor pressure effects on void rupture and crack growth resistance

Purpose – The purpose of this paper is to compare the reliability and intermetallic layer (IML) of solder joints prepared with infrared (IR) and vapour phase (VP) soldering. The reliability of 0603-sized resistors’ solder joints formed with IR and VP soldering was investigated. The IML of the joints was analysed based on image processing algorithm automatically. Design/methodology/approach – For the reliability analyses, the ageing method was a highly accelerated stress test (HAST) with +105°C maximum temperature, fully saturated (100 per cent) relative humidity at +0.5 atm overpressure. The joints were characterised based on the thickness of their IML and on their shear strength in as-reflowed stage, and after 400, 800, 1,200, 1,600 and 2,000 hours of HAST. An image processing algorithm was developed to measure the thickness of the IMLs on cross-sectional scanning electron microscopy (SEM) images automatically. Findings – The increase of the IML thickness is lower in the case of HAST ageing compared to o...

Comparing the reliability and intermetallic layer of solder joints prepared with infrared and vapour phase soldering

Multi-physics modelling of a vapour phase soldering (VPS) system

Vapor pressure and thermal stress induced growth and coalsecence of microvoids near interfaces of die/die-attach and die-pad/moulding compound is recognised as the precursor to interface delamination and popcorn cracking of plastic electronic packages. When exposed to humid ambient conditions prior to reflow soldering, plastic electronic packages absorb moisture, which condenses within the numerous micropores in the substrate, die attach, moulding compounds and in the vicinity of interfaces joining the different material layers. During reflow soldering, moisture in these micropores is vaporized. A representative material cell containing a single microvoid is used to investigate void growth under combined vapor pressure and thermal stress. A critical surface traction, the sum of the internal vapor pressure and the externally applied stress, defines the onset of unstable void growth. Existence of “large” microvoids lowers significantly the critical stress levels for unstable void growth. These stress levels are consistent with generally accepted estimates of stress levels for popcorn cracking given in the literature. Vapor pressure effects can be incorporated into a continuum description of stresses and strains and the Gurson-Tvergaard void growth model providing a new capability for full-field analysis of popcorn cracking in electronic packages.

Thermal and vapor pressure effects on cavitation and void growth

Mode III stress intensity factors for edge-cracked circular shafts, bonded wedges, bonded half planes and DCB’s

An interfacial edge crack of a length a in two bonded dissimilar anisotropic quarter planes having an anti-plane singularity such as a screw dislocation or anti-plane line force is analyzed. The energy release rate and stress intensity factor are explicitly expressed in terms of complex potentials. The interaction problems in two bonded orthotropic quarter planes are exemplified. It is confirmed that the present solution reduces to the known solutions dealing with particular cases of the present problem.

Kyung W. Lee

Papers

An interfacial edge crack in anisotropic bimaterial under anti-plane singularity

Effect of geometric parameters on popcorn cracking in plastic packages during VPS process

A screw dislocation interacting with an interfacial crack in two anisotropic thin films with finite thickness