Metrology of Thin Layers in IC Packages Using an Acoustic Microprobe: Bondline Thickness

摘要

A nondestructive technique is demonstrated for the metrology of adhesive layers that are considerably thinner than a single wave- length of ultrasound in that material. The acoustic microprobe technique discussed in this publication is capable of measuring the thickness and elastic properties of a thin layer sandwiched between two relatively thicker layers. Automated measurement over a 50 pm diameter spot are possible with this technique. The particular case of a silicone adhesive layer between an aluminum lid and a die in a Flip Chip package is discussed in this work The thickness is estimated via an algorithm that minimizes the averaged residual error between the experimental response and theoretical prediction of a transfer function. The thickness of the Sylgard 577 adhesive was measured down to about 5 μm using transducers with nominal center frequencies of 50 and 100 MHz The average error of the acoustic microprobe technique was verified by destructive sectioning to be approximately 0.5 μm. The minimum measurable thick- ness limit of the acoustic microprobe technique is several times better (Smaller) than that of time based techniques using the same transducer