Adhesion tensile pull test

One of the simplest and most useful tests performed on reflow-attached flip chips to determine the adequacy of the solder joints (i.e., C4) is a tensile pull test (Fig. 31). This is done by adhesively attaching a metal stud to the back of a joined chip and pulling the joints in tension at a slow strain rate (approximately 1.0x10 sec ). The pull force is measured during the test using an appropriate load cell. The pull strength is a useful parameter, but the failure mode is a very important indicator of joint quahty. Planar failure at the solder joint interfaces is indicative of a weak and unacceptable interface condition. 

As pointed out by Milewski (1993), the tensile test methods can be subdivided into (i) tests in which the coatings are being pulled off from the substrate with the help of a counter fixture glued or soldered to the coating and (ii) tests in which the coatings are pulled off from an appropriately formed auxiliary fixture without an adhesive (Ollard-Sharivker test). 

Tensile strength, Tensile strength is evaluated by pull testing on metal lap-shear coupons, most often aluminum. The standard test method is ASTM D1002, Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to-Metal) Alumi-... 

Little information exists on the effects of surface pretreatment on bond strength and durability, and there is a general absence of appropriate test methods to assess such effects on adhesion. The pull-off test(68) is, perhaps, currently the most suitable the slant-shear test, as described in BS 6319(69), is of limited use in assessing adhesion because the interfaces are not subjected to tensile forces. 

Saret 633 was evaluated in a T-pull adhesion test using the EPDM formulation described in the materials section (see Section 8.3.1.1). The T-pull test measures the adhesion between rubber and a fibre. The fibre is placed in a mould and rubber is then added and cured. The fibre is then pulled in a perpendicular direction from the rubber and the force to break the adhesive bond is measured. The T-pull test is accomplished by using a special mould with a grid of trenches into which can he laid ruhher and perpendicular to the rubber a filament. By filling the trench half way with the ruhher the filament is embedded. After curing, the filament and rubber resemble a cross. The tensile tester is used to strip the rubber from the filament. 

O Figure 22.8 is a schematic of the tensile adhesion test, where the adhesive is filled into the space between two adherends and two spacers. In the tensile adhesion test, after the spacers are removed from the specimen, the adhesive is pulled at a constant rate. When a given elongation (i.e., 25%, 100%, etc.) is reached, the specimen is fixed for a long time (e.g., 24 h) with the spacers, and the failure type (cohesive or adhesive) is recorded. 

Table 3.3 Tensile testing (pull only) results of commercial and developing adhesives...

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