Effect of annealing temperature on dual-structure coexisting precipitates in Cu–2.18Fe–0.03P alloy and softening mechanism at high temperature.

The Cu–Fe–P alloy is the mainstream material of IC lead frame at present, which plays a key role in electrical signal transmission and mechanical fixation between bearing chip and external circuit board. With the development of integrated circuits toward high integration and extreme miniaturization, copper alloy strips for lead frames are required to have excellent electrical and mechanical properties, as well as excellent softening resistance under short-term high temperature service conditions. In this paper, the effects of annealing temperature (300, 400, 500 °C) on texture orientation and strength, and precipitates characteristics (morphology, size, interfacial relationship, etc.) of as-cold rolled Cu–2.18Fe–0.03P alloy were studied by means of EBSD and TEM. It is found that annealing at low temperature does not change the texture type, but it affects the texture strength compared with the as-cold rolled alloy. Cubic texture {001} < 100 > and R-type texture {111} < 112 > appear in the annealed alloy. The texture strength increases with the increase in annealing temperature, and the preferred orientation is more obvious. In addition, we found that there are two kinds of precipitated phases in the copper matrix, namely spherical α-Fe phase and irregular Fe₃P phase. We further find out the coexistence state of the two precipitates and their evolution with annealing temperature. With the increase in annealing temperature from 300 to 500 °C, the size of the main strengthening phase α-Fe increases and the orientation relationship between α-Fe phase and the matrix changes from coherent to semi-coherent. On this basis, we found that the decrease in texture strength, the change of coherence relationship of α-Fe phase, and the decrease in dislocation barrier are the main factors leading to the softening of Cu–2.18Fe–0.03P alloy at high temperature. The research results of this paper are meaningful in guiding the development of high-end copper alloy strip in the field of electronic information. [ABSTRACT FROM AUTHOR]