Mechanical Modeling of Stress Generation During Cure of Encapsulating Resins

Conference · Thu Feb 28 23:00:00 EST 1991 · Materials Research Society Symposia Proceedings

DOI:https://doi.org/10.1557/proc-225-177· OSTI ID:5844388

Lagasse, R. R. ^[1]; Chambers, R. S. ^[1]; Guess, T. R. ^[1]; Plazek, D. J. ^[2]; Bero, C. ^[2]

---

1. Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
2. Univ. of Pittsburgh, PA (United States)

We have developed a numerical model for calculating stresses generated during cure of shrinking encapsulating resins. Mechanical modeling of polymer encapsulated electronic devices usually focusses on stress generated during cooling after cure. The stress developed during cure, due to shrinkage of the encapsulant, is normally neglected. That assumption is valid if both the shear and bulk moduli of the encapsulant at the cure temperature are negligible with respect to the moduli at lower temperatures. Our measurements on a model epoxy encapsulant show that the shear modulus during cure, varying from 0 to 6 MPa, is at least 100 times smaller than that at ambient temperature. In contrast, the bulk modulus at the cure temperature is only 2.5 times smaller. Since the bulk modulus during cure cannot be neglected, significant stress can be produced if volume shrinkage is constrained by a stiff mold or embedded elements. In fact, mechanical failure of encapsulating materials during cure has been evident in some of our experiments. Using measurements of shear and bulk moduli plus volume shrinkage as inputs to a finite element model, we have successfully predicted the shrinkage strains and stresses developed during cure of a model epoxy resin inside a cylindrical tube. Consideration of cure shrinkage stress has led to a process modification that appears to reduce mechanical failures in a real encapsulated device.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 5844388
• Report Number(s): SAND--90-3033C; CONF-910406--4; ON: DE91011496
• Journal Information: Materials Research Society Symposia Proceedings, Journal Name: Materials Research Society Symposia Proceedings Vol. 225; ISSN 0272-9172
• Publisher: Springer Nature
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
97 MATHEMATICS AND COMPUTING
99 GENERAL AND MISCELLANEOUS
990200 -- Mathematics & Computers
CURING
ENCAPSULATION
FAILURES
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PETROCHEMICALS
PETROLEUM PRODUCTS
POLYMERS
RESINS
SHEAR PROPERTIES
SHRINKAGE
STRESSES