Copper foil is an important material for the manufacture of copper clad laminate (CCL) and printed circuit board. In the high-speed development of electronic information industry, copper foil is called "neural network" of electronic product signal and power transmission and communication. Therefore, for our testing industry, the physical properties of copper foil testing method is particularly important.

Tensile strength and ductility are two important physical properties of copper foil. The main criteria for testing these properties are ipc-tm-6502.4.18.1A, ASTM E345-2016, GB/t 5230-1995, GB/t 5187-2008 and Gb/t 228.1. The following is a brief description and analysis of these standards.

At present, the most commonly used test standard is ipc-tm-6502.4.18.1A, which is specially developed for copper foil of printed circuit board. Its detection methods and key points are as follows:、

I. The thickness of copper foil ranges from 0.05 mm to 0.1 mm

II. The sample is strip or lead sample, 5 in transverse and 5 in Longitudinal. The strip sample size is 13mm 150mm. The lead sample size is Astm E345a (more on that later)

III. The distance of the gauge is 50mm, the movement rate of the chuck is 0.05mm/mm ~ 0.5MM/MM per minute (this is the strain rate, the specific test rate needs to be converted according to the distance between the chuck)

IV. The samples were cut and roasted at 125 ± 5 °C for 4ー6 hours

V. Failure determination: The sample has obvious defects leading to fracture; the result deviates from the average value. This method provides most of the test parameters, but three points are not clearly written: one is the numerical correction; the other is the chuck spacing, which also affects the choice of test rate, because the actual test rate is obtained by multiplying the chuck spacing by the strain rate, and the third is the judgment of failure, that is, how the test result is judged to be valid, although it is clearly stipulated that the distance is 50 mm, the position of the marking line is not clearly stated, that is to say, there is no special strict requirements on the location of the fracture, in the actual test, the location of the fracture is often the thinnest part of the copper foil, not necessarily in the middle of the fracture is accurate.

The above mentioned sample a in ASTM E345, the sample size is as follows:

Total length l ≥200mm;

Distance g = 50.0 ± 0.1 mm;

Middle Parallel length a ≥60;

Length of both ends B ≥50mm;

The width of the narrow part is 12.5 ± 0.25 mm.

Here, remove the two end clamping part B, the middle part is equivalent to the distance between the chuck, about half of the total length, the middle parallel length a ≥60 mm. According to the choice of the chuck spacing, the Chuck spacing of the Strip specimen without the head can be between 60mm and 75mm.

ASTM E345-16 is the standard test method for tensile testing of metal foils. The main parameters are as follows, compared with IPC-TM-6502.4.18.1A:

I. The method can be used to test metal foil with thickness ≤0.2 mm

II. Two types of specimens: TYPE A and type B. As mentioned above, the type a specimen is a non-headed specimen: the total length is ≥230 mm, the width is 12.5 mm, the gauge distance is 125 mm, and the distance between the recommended chucks is 125 mm, so the elongation can be calculated directly by the displacement between the chucks after fracture

III. The strain rate is 0.06ー0.5 MM/MM/MIN when the yield is not determined, and 0.002ー0.010 mm/mm/min when the yield is tested

IV. Reduction: STRENGTH VALUE TO 1 MPA, elongation to 0.5% .

This method is for the performance of metal foil testing, not specifically for copper foil and does not mention the cut after the baking requirements. But the standard has clear instructions for judging the failure: The sample has obvious defects or scratches; the surface of the sample is badly processed; the sample size does not meet the requirements; the sample is broken due to mechanical reasons; the test method is not correct; When the elongation is measured with sample a, the fracture position of the sample is not within 1/2 of the center distance. That is to say, if the distance between chucks is 80 mm with type A specimen, the fracture position is valid in the middle 40 mm range.

In Appendix D of GB/t 5230-1995 for electrolytic copper foil, the test requirements for electrolytic copper foil are as follows: 

I. Sample Size: 200 ± 0.5 mm in length, 15 ± 0.25 mm in width. Sample number: 4(2 in Horizontal and 2 in Vertical) ;

II. Standard Distance 50mm, the distance between the standard line and the chuck is not less than 3mm;

III. The distance between chucks is 125mm, the chucking speed of the testing machine is 50mm/min;

IV. Test Temperature: 20 ± 10 °C;

V. The result: take four arithmetic mean of the results of the experiment. This method briefly explains the judging methods of invalid result: Specimen breaking out of standard distance, improper operation (such as sample clip deviation) , sample itself defect, data deviation caused by recording error or other reasons. It is worth mentioning that the distance of the marking line from the chuck is not less than 3mm, and there is no clear provision that the marking line must be drawn in the middle part. Therefore, it can be considered that the fracture position is not less than 3mm from the chuck is effective.

In Appendix B to Gb/t 228.1-2010, for specimens of thickness 0.1 mm ~ 3 mm of sheet and Strip, it is specified that for specimens with no head of width equal to or less than 20 mm, the original gauge l 0 shall be equal to 50 mm, unless otherwise specified in the product, the free length between the CHUCKS SHOULD BE EQUAL TO L 0 + 3 B 0. That is, if the sample width is 12.5 mm, then the distance between chucks should be 87.5 mm. This size is similar to the size of copper foil mentioned in Ipc-tm-6502.4.18.1 A. The distance between chucks can be 50 + 13 = 89 mm. In terms of numerical correction, the standard refers to the correction of strength performance values to about 1 MPA and other elongation values other than yield point elongation to about 0.5% , which is consistent with the correction standards in ASTM E345-16 and ISO 6892-1:2009, this is also the way we currently choose to amend the contract.

As mentioned in Gb/t 5187-2008 for copper and copper alloy foils, the selection of the copper foil tensile test method GB/t 228 specifies that the type of specimen is P02. This method is not often used and will not be repeated here.

According to the above analysis, there are still some differences in the choice of the distance between the copper foil drawing chucks and the judgement of the result. For the ipc-tm-6502.4.18.1a standard commonly used in the printed circuit board industry, there is currently a greater degree of freedom in the application of these two points, we feel that in the subsequent update of the standard should be necessary to add these two points.

[ REF. ]

Ipc-tm-6502.4.18.1a Tensile Strength and Elongation, In-House plating. [2] E345-16 Standard Test Methods of Tension Testing of metallic foil. GB/t 5230-1995 electrolytic copper foil. GB/t 228.1-2010 metallic materials-tensile test-part 1: Test Method at room temperature. GB/t 5187-2008 copper and copper alloy foil. 

Source: The web

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