Comparative study of NiNiP leadframes from different processes

Abstract

In this study, Ag/NiNiP-plated Cu leadframes from two different processes are compared in terms of NiNiP surface morphology, composition of NiP layer, grain structures of Ni and NiP plated layers, and impurities in the interface of Ni/NiP plated layers. Their impacts were assessed after solder plating and baking. Scanning electron microscopy (SEM) shows that the grain size of Leadframe A (from Process A) is relatively larger than that of Leadframe B (from Process B). The Auger electron spectroscopy (AES) analysis shows both leadframes have comparable P-content (typically around 12.5% by atom or 6.99% by weight) in their NiP layer after 20 nm sputtering. The focused-ion-beam (FIB) cut shows that the Ni layer of Leadframe A shows both big and small grains; the Ni layer of Leadframe B shows more uniform intermediate grain sizes. However, the grain structures of their NiP layers are very different. The NiP layer of Leadframe A appears amorphous and is clearly distinguishable from the Ni layer, but the NiP layer of Leadframe B looks grainy and its interface with the Ni layer is not very distinguishable. The depth profile of the time-of-flight secondary ion mass spectroscopy (TOF-SIMS) shows that there are higher copper, potassium and chloride impurities in the Ni and NiP interface for Leadframe A while those impurities in Leadframe B are much lower. The different characteristics of plated layers observed in the two leadframes are related to the chemical systems and process parameters used by the two leadframe processes. The impacts of these differences were detected after solder plating and post-plating baking. Leadframe B is able to pass 100 hours of baking at 155°C without any observed abnormality. By contrast, Leadframe A is only able to sustain 30 hours of baking at 155°C. Further baking on Leadframe A causes the NiP layer to peel from the Ni layer of the leadframe. This study demonstrates that the quality of NiNiP plated layer is very critical to the adhesion of Ni and NiP interface which might affect the package performance in the later stage. Further and deep study is needed to understand the failure mechanism of NiP peeling from the Ni layer after the baking test.