PC test does not reveal degradation . Thereby it can be concluded |
shift of the critical degradation from below the chip to the edges |
that bond failure will not be an issue for the new joint technology |
of the DCB . |
. XT . |
On the other hand , a further reduction of t on is expected to result |
The degradation pattern in the baseplate solder can be analyzed |
in significantly higher lifetime – independent from ΔT – as the |
by means of scanning acoustic microscopy ( SAM ). Figure 4 depicts |
stress in the substrate-to-baseplate solder is reduced significantly . |
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the results and underlines the impact of ton . For t on= 2 s , the degradation of the solder starts directly below the chip ( Figure 4 a ). Increasing t on from 2 to 5 s leads to a higher ΔT at the edges of the substrate-to-baseplate solder joint which in turn manifests itself in additional shear forces and a more dominant degradation at the edges compared to the beginning of the test ( Figure 4 b ). It has to be underlined , that the sample from Figure 4a afterwards reached more than 6∙106 cycles .
When ton is increased even further to 60 s , this effect becomes even more apparent as degradation is strongly accelerated at the edges of the baseplate-solder ( Figure 4c ). For this load , the degradation pattern bears strong resemblance to that obtained after passive thermal cycling . With the findings from it can be expected that a further increase of t on would lead to a complete
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Summary
In contrast to standard joining technology , the wire-bond related failure loses importance as bond failure can be excluded with . XT .
By increasing t on, the degradation of the baseplate solders joint shifts from below the chips toward the substrate ´ s edges and becomes the most prominent EOL mechanism . The . XT lifetime is still dependent on T vjmax and t on but is shifted to much higher numbers of cycling .
Based on this and in comparison to EOL mechanism of standard joining technologies , aluminum wire-bond and soft-soldering die attach , the . XT joining technology provides a major advantage with respect to lifetime . The described results of the lifetime research will be implemented in new lifetime models of the innovative . XT interconnect technologies .
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