Tensile-Shear Strength Test - SMD (Surface Mounted Device) Component

Tensile-shear strength testing is a crucial mechanical evaluation method used in electronics manufacturing to assess the reliability and quality of solder joints between surface-mounted components (resistors, capacitors, chip resistors, or LED packages) and printed circuit board (PCB) pads. This method measures how much force the solder joint can withstand under tensile (pulling) or lateral (shear) loading and helps identify issues such as poor wetting, voids, intermetallic compound weakness, insufficient solder volume, or process defects.

SMD solder joints are subjected to thermal cycling, vibration, mechanical shock, and drop impacts in real-world applications (e.g., smartphones, automotive electronics, or industrial devices). Tensile and shear tests provide quantitative data on bond strength, complementing visual inspection (according to the IPC-A-610 standard), X-rays, or sectioning. They help validate soldering processes, template design, reflow profiles, and material selections.

The main types of tests for SMD solder joints are as follows:

Shear strength test: Applies a horizontal (lateral) force parallel to the printed circuit board (PCB) surface to push or cut the component. This method is most common for lead-free SMDs and some leaded packages. During the test, a chisel-like or flat cutting tool is placed against the side of the component body and moved horizontally at a controlled speed. Failure modes include: solder breakage, pad lift, component body fracture, or adhesion/bonding failure.

Typical standards for this method include:

IEC 62137-1-2 Surface mount technology - Part 1-2: Mechanical shear strength testing of solder joints.
Certain sections of the IEC 60068-2-21 standard (Environmental testing - Test U: Robustness of terminations and integrated assembly devices)
JEITA ET-7409/103 standard (torque cutting method for certain situations)
Tensile strength test: Applies a tensile force (upward/outward) to the printed circuit board (PCB) at a perpendicular or angle. Common variants include:
Hook pulling or tweezer pulling for leaded components.
Cold pulse pulling for BGA/CSP solder balls: grips and pulls a single ball upwards.
Pull at a 45-degree angle for a general connection assessment.

During testing, a hook, tweezer holder, or pliers is attached to the component tip/body and pulled vertically or at an angle.

Typical standards for this method include:

IEC 62137-1-1 (tensile strength test of solder joints)
JEDEC JESD22-B115 (for cold impact drawing)

Typically, for better access and realistic stress application, the printed circuit board (PCB) needs to be fixed at a 45-degree angle.

Many modern joint testing machines combine both tensile and shear capabilities in a single system with automatic alignment, force/load cells (typically in the 0-100 kg range), and failure mode analysis software.

A typical procedure follows these steps:

The printed circuit board (PCB) is securely mounted to a fixture (vertical for cutting, angled for pulling).
The instrument is precisely aligned with the component (using an XY stage and microscope).
Force is applied at a controlled rate (e.g., 0,1-10 mm/min depending on the standard).
Peak force and failure mode are recorded.
Acceptance criteria are used for comparison (usually on a customer-specific basis or according to IEC/JEDEC minimums, depending on the solder area or component mass).

Fault analysis and interpretation:

Good connection: High-force bulk soldering fractures (ductile shear).
Weak connection: Crater formation in the pad, brittle intermetallic fracture, or low strength. This indicates process problems (e.g., excessive void formation, fouling, poor reflow).

Tensile-shear strength testing is a necessary destructive mechanical test in electronics manufacturing and reliability engineering for various critical reasons.

The main reasons why this method is important are as follows:

Measures true mechanical strength and reliability: Solder joints in SMD components must withstand not only electrical bonding but also mechanical forces throughout the product's lifespan. Tensile and shear tests apply controlled tensile (pulling) or lateral (shearing) loads to measure the peak force required to cause failure. This provides objective, numerical data on bond strength that visual or X-ray methods cannot reliably provide.
It detects hidden or subtle defects that non-destructive methods miss: Many critical weaknesses are invisible or difficult to detect without applying stress.
Brittle intermetallic compound layers formed during reflow or aging.
Excessive gaps, poor wetting, insufficient solder volume, or contamination.
Poor pad adhesion or early-stage pad cratering.
Changes resulting from miniaturization (smaller links have different stress distributions, with IMC thickness becoming proportionally more dominant).

These problems often lead to low-strength failures. This test quantifies these failures.

It simulates real-world mechanical stresses and failure modes: Electronic products face the following:
Transport and assembly stresses (e.g., circuit board removal, connector installation, in-circuit testing).
Vibration and shock (automotive, aviation, consumer devices during falls or transportation).
Thermal-mechanical cycling (expansion/contraction mismatches).

Shear testing simulates lateral forces, while tensile testing simulates tensile/out-of-plane loads. High-speed variants show a good correlation with drop/shock performance.

It supports process verification, qualification, and continuous improvement: Manufacturers use pull-cut data in the following situations:
Process characterization: New solder pastes, stencil designs, or surface coatings.
Incoming inspection of components/cards.
Failure analysis after reliability stresses (thermal cycling, aging, drop testing).
Comparison between suppliers or parties.
It complements other methods: while sectioning reveals the microstructure and staining and removal reveal crack patterns, tensile-shear measurements provide fast, repeatable, force-based measurements.

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