ASTM F641-98a

Standard Specification for Implantable Epoxy Electronic Encapsulants

SCOPE
1.1 This specification covers thermoset plastics based on diglycidyl ethers of bisphenol A and amino functional curing agents or amine catalysts.  
1.2 The epoxy encapsulants covered by this specification are intended to provide a tissue-compatible protective covering for implantable medical devices such as pulse generators, telemetry devices and RF receivers. The biocompatibility of epoxy plastics has not been established. Epoxy plastic is a generic term relating to the class of polymers formed from epoxy resins, certain curing agents or catalysts and various additives. Since many compositions and formulations fall under this category, it is essential that the fabricator assure safety of implantability of the specific composition or formulation for the intended use by current state-of-the-art test methods. This specification can be used as a basis for standardized evaluation of biocompatibility for such implantable encapsulants.  
1.3 The encapsulants covered by this specification are for use in devices intended as long-term implants.  
1.4 Limitations- This specification covers only the initial qualification of epoxy encapsulants for implantable electronic circuitry. Some of the requirements are not applicable to routine lot to lot quality control.

General Information

• Status: Historical
• Publication Date: 09-Oct-1998
• Technical Committee: F04 - Medical and Surgical Materials and Devices
• Drafting Committee: F04.11 - Polymeric Materials

Relations

• Replaced By: ASTM F641-98a(2003) - Standard Specification for Implantable Epoxy Electronic Encapsulants
• Effective Date: 10-Apr-2003
• Referred By: ASTM F2027-16 - Standard Guide for Characterization and Testing of Raw or Starting Materials for Tissue-Engineered Medical Products
• Effective Date: 10-Oct-1998

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 641 – 98a
Standard Specification for
Implantable Epoxy Electronic Encapsulants
This standard is issued under the fixed designation F 641; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 150 Test Methods for A-C Loss Characteristics and
Permittivity (Dielectric Constant) of Solid Electrical Insu-
1.1 This specification covers thermoset plastics based on
lating Materials
diglycidyl ethers of bisphenol A and amino functional curing
D 257 Test Methods for D-C Resistance or Conductance of
agents or amine catalysts.
Insulating Materials
1.2 The epoxy encapsulants covered by this specification
D 570 Test Method for Water Absorption of Plastics
are intended to provide a tissue-compatible protective covering
D 638 Test Method for Tensile Properties of Plastics
for implantable medical devices such as pulse generators,
D 790 Test Methods for Flexural Properties of Unreinforced
telemetry devices and RF receivers. The biocompatibility of
and Reinforced Plastics and Electrical Insulating Materi-
epoxy plastics has not been established. Epoxy plastic is a
als
generic term relating to the class of polymers formed from
D 883 Terminology Relating to Plastics
epoxy resins, certain curing agents or catalysts and various
D 1042 Test Method for Linear Dimensional Changes of
additives. Since many compositions and formulations fall
Plastics Under Accelerated Service Conditions
under this category, it is essential that the fabricator assure
D 1239 Test Method for Resistance of Plastic Films to
safety of implantability of the specific composition or formu-
Extraction by Chemicals
lation for the intended use by current state-of-the-art test
D 1434 Test Method for Determining Gas Permeability
methods. This specification can be used as a basis for stan-
Characteristics of Plastic Film and Sheeting
dardized evaluation of biocompatibility for such implantable
D 1763 Specification for Epoxy Resins
encapsulants.
D 1898 Practice for Sampling of Plastics
1.3 The encapsulants covered by this specification are for
D 2240 Test Method for Rubber Property—Durometer
use in devices intended as long-term implants.
Hardness
1.4 Limitations—This specification covers only the initial
D 2471 Test Method for Gel Time and Peak Exothermic
qualification of epoxy encapsulants for implantable electronic
Temperature of Reacting Thermosetting Resins
circuitry. Some of the requirements are not applicable to
D 2562 Practice for Classifying Visual Defects in Parts
routine lot to lot quality control.
Molded from Reinforced Thermosetting Plastics
1.5 This standard does not purport to address all of the
D 2566 Test Method for Linear Shrinkage of Cured Ther-
safety concerns, if any, associated with its use. It is the
mosetting Casting Resins During Cure
responsibility of the user of this standard to establish appro-
D 2734 Test Method for Void Content of Reinforced Plas-
priate safety and health practices and determine the applica-
tics
bility of regulatory limitations prior to use.
D 3137 Test Method for Rubber Property—Hydrolytic Sta-
2. Referenced Documents
bility
F 74 Practice for Determining Hydrolytic Stability of Plas-
2.1 ASTM Standards:
tic Encapsulants for Electronic Devices
D 149 Test Method for Dielectric Breakdown Voltage and
F 135 Test Method for Embedment Stress Caused by Cast-
Dielectric Strength of Solid Electrical Insulating Materials
ing Compounds on Glass-Encased Electronic Components
at Commercial Power Frequencies
F 602 Criteria for Implantable Thermoset Epoxy Plastics
1 3
This specification is under the jurisdiction of ASTM Committee F-4 on Medical Annual Book of ASTM Standards, Vol 08.01.
and Surgical Materials and Devices and is the direct responsibility of Subcommittee Annual Book of ASTM Standards, Vol 15.09.
F04.11 on Polymeric Materials. Annual Book of ASTM Standards, Vol 09.01.
Current edition approved October 10, 1998. Published March 1999. Originally Annual Book of ASTM Standards, Vol 08.02.
published as F 641 – 79. Last previous edition F 641 – 98. Annual Book of ASTM Standards, Vol 10.04.
2 8
Annual Book of ASTM Standards, Vol 10.01. Annual Book of ASTM Standards, Vol 13.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 641 – 98a
F 748 Practice For Selecting Generic Biological Test Meth- 5.1.2 Fully Cured Specimens—The required properties
ods for Materials and Devices measured on fully cured specimens conditioned as in 6.1 are as
F 895 Test Method for Agar Diffusion Cell Culture Screen- follows:
ing for Cytotoxicity 5.1.2.1 Transparency—In cases where no fillers or rein-
F 981 Practice for Assessment of Compatibility of Bioma- forcements are used, the encapsulant shall have sufficient
terials for Surgical Implants with Respect to Effect of transparency so that the circuitry may be visually inspected
Materials on Muscle and Bone after encapsulation.
2.2 AAMI Standard: 5.1.2.2 Foreign Particles—No foreign particles, particulate
EOS-D E-O Sterilization Standard matter and gross contamination shall be observed when
checked under 23 wide field magnification.
3. Classification 5.1.2.3 USP Biological Tests Plastic Containers, Class
IV —Pass.
3.1 Encapsulants shall be classified as follows:
5.1.2.4 USP Pyrogen Test or other Pyrogen methods
3.1.1 Type I—Those encapsulants which contact the tissue
which have been demonstrated to be of equal or greater
directly or indirectly.
sensitivity—Pass.
3.1.2 Type II—Those encapsulants used only within her-
5.1.2.5 Sterilant Residues (AAMI EOS-D)—Where appli-
metically sealed containers. The epoxy encapsulant has no
cable, the concentration of ethylene oxide, ethylene chlorohy-
contact with tissues or physiological fluids.
drin, ethylene glycol, and dichlorodifluoromethane (or the
equivalents) at the time of implant shall be shown to be within
4. Chemical Composition
safe limits prescribed by the device manufacturer.
4.1 Additives (Type I Encapsulants Only):
5.1.2.6 The cure shrinkage (Test Method D 2566) or em-
4.1.1 Reactive Diluents—The following compounds when
bedment stress (Test Method F 135) shall be #2%. The stress
used as reactive diluents shall not be used in concentrations
shall not exceed the limits of the most pressure-sensitive
greater than 12 parts per hundred resin (phr).
components.
4.1.1.1 Butyl glycidyl ether (BGE).
5.1.2.7 Tissue Culture Test (Agar Overlay) or Test Method
4.1.1.2 Phenyl glycidyl ether (PGE).
F 895—Pass.
4.1.2 Other Additives (see Note 1)—Other additives shall be
5.1.2.8 While cell culture methods as described in Test
shown to be nonextractable in 37°C physiological saline for the
Method F 895 may be appropriated for the batch-to-batch
device design life in concentrations sufficient to significantly
screening of fully cured specimens, the basic recipe used
affect the properties of the encapsulant or to produce a
should have been qualified for its overall tissue response by
significant biological reaction.
methods such as those suggested in Practice F 748 for “Im-
NOTE 1—Other additives, as indicated in Criteria F 602, include planted Devices Principally Contacting Tissue and Tissue
compounds such as nonreactive diluents, fillers, release agents, and the
Fluid” including testing according to Practice F 981.
like.
5.1.3 Required Cured Properties Measured in Long-Term
Immersion Tests for Type I Encapsulants—The property values
4.1.3 Phthalate Esters—Phthalate esters such as dibutyl
phthalate shall not be used in concentrations $10 phr. prescribed in Table 1 shall be obtained at 22 6 3°C and 50 6
10 % relative humidity on specimens conditioned as in 6.3.
4.2 Mix Ratios (Type I and Type II Encapsulants):
4.2.1 Amines—The mix ratio shall be maintained at 65 Samples shall be wiped dry prior to test with a lint-free tissue,
as appropriate.
equivalent % of stoichiometry.
5.1.4 Optional cured properties measured after accelerated
4.2.2 Catalysts—The mix ratio shall be maintained within
immersion for Type I encapsulants may be determined for
the ranges recommended by the formulator.
screening purposes after conditioning as in 6.2.
4.3 Carbonates (Type I and Type II Encapsulants)—The
5.2 Type II Encapsulants:
encapsulant shall be poured under conditions such that the
5.2.1 Peak Exotherm Temperature (Test Method D 2471)—
formation of amine carbonates is minimized. The device
The peak exotherm temperature during cure shall be kept
manufacturer may specify maximum limits of carbon dioxide
below the maximum acceptable value for the lowest tempera-
or water vapor, or both, in the atmosphe
...