Acoustic Inspection of Hybrid Systems on Laminated Substrates

Confocal Scanning Acoustic Microscopy

Summary

Hybrid microelectronics within plastic packages are comprehensively inspected thanks to the con-focal resolution provided by the scanning acoustic microscopy technique. The high depth resolution allows us to resolve the top and inner metallic layers of the laminate.

Remarks

Con-focal scanning acoustic microscopy is used to thoroughly inspect features at different layers of hybrid multichip modules (MCM). The inspection does not reveal rejectable features at the different discrete components included in this assembly, either active (ICs and semiconductor dice) or passive (resistors, capacitors, and inductors) and over the top metallic layer. Non-circuit side inspection is used to assure the lack of delamination within the laminate (e.g. inner metallic layers).

Assessment as per different test methods

In Alter Technology scanning acoustic tomography inspection of plastic encapsulated microcircuits (PEMs) and similar systems is conducted by different inspection methods (J-STD-020E, ESCC 25200, PEM-INST-001, MIL-STD-1580 and others). Nonetheless, in the matter at hand, specification J-STD-020E is the most suitable as it includes specific requirements for the inspection of substrate-based packages, such as the laminated multichip module (MCM-L) herein analyzed. In this case, no anomalies are observed in agreement with this specification.

Sample & Method

A RF Variable Gain Amplifier (VGA) module encapsulated in a MCM package is investigated. Probe frequencies and inspection procedure are adapted to the internal structure of this plastic encapsulated microelectronic part. In this case the architecture of the system includes both thick and thin discrete components onto a multilayer laminates substrate. Therefore, circuit side inspection is conducted using a low frequency transducer to extend the depth of field whereas the high frequency transducer used during the non-circuit side inspection allows us to resolve inner conductive layers within the laminate.