Tensile Strength, Elongation, and Modulus

1 The Institute for Interconnecting and Packaging Electronic Circuits Number 2215 Sanders Road Northbrook, IL 60062-6135 Subject Tensile strength , Elongation, and Modulus Date Revision 7/95. IPC-TM-650 Originating Task Group TEST METHODS MANUAL Deposited Dielectric Task Group (C-13a). Scope This test method establishes a procedure for equipped with a load cell whose compliance is a maximum of determining the Tensile strength , elongation and Young's 2% of the specimen extension within the range being mea- Modulus of organic free films. sured. Digital (as opposed to analog) self-calibrating load cells are preferred since they eliminate the need for and potential Applicable Documents error associated with calibrating analog load cells using exter- nal weights. The testing machine must be equipped with a ASTM D 618 Standard Practice for Conditioning Plastics and device for recording the Tensile load and the amount of sepa- Electrical Insulating Materials for Testing ration of the grips; both of these measuring systems should ASTM D 882 Standard Test Methods for Tensile Properties be accurate to 2%.

2 The rate of separation of the grips shall of Thin Plastic Sheeting be accurate to and capable of adjustment from approximately 0 to 50 mm/min. ASTM D 1005 Standard Test Methods for Measurement of Dry-Film Thickness of Organic Coatings Using Micrometers Gripping Devices A gripping system that minimizes ASTM D 2370 Standard Test Method for Tensile Properties both slippage and uneven stress distribution must be used. of Organic Coatings The grips must be self-aligning, they must be attached in such a manner that they will move freely into alignment as Test Specimen The test specimen shall consist of a soon as any load is applied so that the long axis of the speci- strip mm wide by mm in length and at least 10 men will coincide with the direction of the applied pull through m in thickness. The width of the specimen should not devi- the center line of the grip assembly. ate by more than 2% over the length of the specimen between the grips. The thickness of the films shall not vary by Grip Faces Specimen slippage and necking of the more than 10% over the entire film.

3 A minimum of ten speci- specimen up into the grips are two of the most common mens are required. problems with this test method. Slippage can be checked by drawing a series of parallel lines across the part of the speci- Apparatus or Material men in the grips. After pulling the specimen, if the lines are not parallel, the specimen may be slipping on one side. On speci- Thickness Measurement Device Mitutoyo 519-605 mens with high elongations, necking of the specimen into the Mini-Checker with a 519-891 probe with vacuum assist con- grips is a problem. As the specimen elongates, the reduction nected to a MUX-10 multiplexer or equivalent thickness mea- of area (necking) results in a loosening of the specimen at the surement device accurate and precise to m. inside edges of the grips. This loosening propagates further back into the grips with continued elongation of the specimen. Width Measurement Device Micrometer or equivalent This can lead to erroneous results for the elongation.

4 Air- width measurement device capable of measuring to mm. actuated grips lined with rubber faces ( , neoprene) that have been machined flat were found to be effective against Specimen Cutter Thwing-Albert JDC Precision Cutter both of these problems and still allowed the specimen to be or equivalent. The specimen cutting device must be capable easily removed from the grips after the test. Another approach of cutting a film strip mm wide over the length of is to use line grips, grips having faces designed to concen- the specimen. It is imperative that the cutting edges be kept trate the entire gripping force along a single line the width of sharp and free from visible scratches or nicks. The use of the specimen perpendicular to the direction of the testing striking dies is not recommended because of poor and incon- stress. This is usually done by combining one standard flat sistent specimen edges. grip face and an opposing grip face that has been cut down. In cases where specimens frequently fail at the edge of the Tensile Tester Instron Model 4501 Tensile Tester with grips, it may be advantageous to round the edges of the grip a kN load cell or equivalent.

5 The testing machine must be faces where they meet the test area of the specimen. Material in this Test Methods Manual was voluntarily established by Technical Committees of the IPC. This material is advisory only and its use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this Page 1 of 3. material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement. Equipment referenced is for the convenience of the user and does not imply endorsement by the IPC. IPC-TM-650. Number Subject Date Tensile strength , Elongation, and Modulus 7/95. Revision Extension Indicators (optional) Extension indicators the initial gauge length (grip separation) at ( , extensometers) must be designed as to minimize stress mm and the rate of grip separation at mm/min. on the specimen at the contact points of the specimen and the indicator. Clip type extensometers are not recommended Place the specimen in the grips of the testing for this reason.

6 Laser extensometers can be used if the machine, taking care to align the long axis of the specimen method of marking the specimen does not induce any stress with an imaginary line joining the points of attachment of the or strain into the specimen ( , scratching the specimen) or grips to the machine. The specimen should be aligned as per- change the specimen in any fashion ( , heating the fectly as possible with the direction of pull so that no rotary specimen). motion that may induce slippage will occur in the grips. Tighten the grips evenly and firmly to the degree necessary to Calibration The thickness gauge should be calibrated minimize slipping of the specimen during testing. The use of every six months using standard gauge blocks. The blades on air activated grips facilitates the mounting of the specimen in the film cutter should be resharpened or replaced at least the grips. once a year. The load cell on the Tensile tester should be cali- brated at least once a week following the manufacturer s rec- Start the test and record the load versus extension.

7 Ommended procedure. Also, the stops which control the ini- tial grip separation should be checked once a week. Repeat steps - for each series of ten specimens. Procedure Calculations Operating Conditions The tests should be conducted at 23 2 C and 50 5% relative humidity. For each series of ten specimens, the arithmetic mean and standard deviation of each property for the specimens Preparation of Test Specimens with the five highest Tensile strengths shall be calculated to the proper number of significant figures. This is done on the basis The test specimens should be conditioned at 23 that the expected errors (nicks or flaws in the specimen, 2 C and 50 5% relative humidity for not less than 24 hours breaks within the grips, specimen slippage, etc.) would all prior to testing. Refer to ASTM D 618. tend to produce lower results. The standard deviation is cal- culated as follows and reported to two significant figures: The free films are placed between two cover sheets of ( ).

8 Clear film (MylarT* or equivalent) to facilitate handling of the N N 2. specimens. N X. i=1. i 2.. i=1. Xi Sx =. N(N 1). Cut at least 10 specimens mm long and mm wide. No specimen shall vary by more than 2% in width where Xi is the value of a single observation (i = 1 through N), along its entire length. The utmost care must be exercised in N is the number of observations, and sx is the estimated stan- cutting specimens to prevent nicks and tears along the edges dard deviation. of the specimen that are likely to cause premature failure. If the properties in the plane of the film are not isotropic ( , Tensile strength Tensile strength is calculated by the films were not prepared by spin coating), then ten films dividing the load at break by the original minimum cross- must be cut in both the machine direction (MD) and transverse sectional area. The result is expressed in megapascals (MPa). direction (TD). and reported to three significant figures. (load at break).

9 Tensile strength =. Testing (original width) (original thickness Measure and record the thickness of the test speci- Percent Elongation Percent elongation is calculated men to an accuracy of m at no fewer than five different by dividing the elongation at the moment of rupture by the ini- places within the gauge length area. Refer to ASTM D 1005 tial gauge length and multiplying by 100. When gauge marks and AST D 2370. or extensometers are used to define a specific test section, Page 2 of 3. IPC-TM-650. Number Subject Date Tensile strength , Elongation, and Modulus 7/95. Revision only this length is used in the calculation, otherwise the dis- tance between the grips is used as the initial gauge length. The result is expressed in percent and reported to two signifi- cant figures. (elongation at rupture) x 100 D. percent elongation =. (initial gage length). Stress Young's Modulus Young's Modulus is calculated by drawing a tangent to the initial linear portion of the stress- strain curve, selecting any point on this tangent, and dividing the Tensile stress by the corresponding strain.)

10 For purposes of this calculation, the Tensile stress shall be calculated by divid- ing the load by the average original cross section of the test C. specimen. The result is expressed in gigapascals (GPa) and reported to three significant figures. A B Strain (load at point on tangent). (original width) (original thickness) Figure 1. Young's modululus =. (elongation at point on tangent). (initial gage length Notes The Tensile properties determined using this test method will vary with method of specimen preparation, speci- Toe Compensation (from ASTM D 882) In a typical men thickness, specimen width, rate of grip separation, initial stress-strain curve (see below), there is a toe region, AC, gauge length, type of grips used, and method of measuring which does not represent a property of the material. It is an extension. The Tensile strength and elongation are sensitive to artifact caused by a take-up of slack, and alignment or seat- the specimen dimensions and any flaws in the specimen.)