Drop testing is a critical step in assessing the mechanical reliability of a product, and its reliability is largely determined during the PCB design and manufacturing stages. The success or failure of drop testing is related to PCB design, PCB manufacturing, and PCBA operations, and this article will elaborate on these three aspects.
★ PCBA Drop Testing
The purpose of drop testing is to simulate whether the PCBA and its components can withstand impacts without functional failure or mechanical damage during accidental drops in transportation, handling, or daily use.
☆☆ Testing Standards
♞ Typically follows international or industry standards, the most common being:
· JEDEC JESD22-B111:
“Board-Level Drop Test Method for Handheld Electronic Products” — This is the most authoritative and commonly used standard.
· IEC 60068-2-27:
“Basic Environmental Testing Procedures – Part 2: Tests – Test Ea and Guidance: Shock”
· Internal Company Standards:
Many companies develop stricter standards based on their product characteristics (such as weight, size, and expected usage environment).
♞ Key Testing Parameters
· Drop Height: The core parameter!! Typically determined based on product weight and expected risk level. The JEDEC standard specifies drop heights corresponding to different product weights (e.g., 1m, 1.5m, etc.), with a common range of 0.75m to 1.5m.
· Impact Pulse Waveform: The impact of the drop platform hitting the ground generates an acceleration pulse. Standards typically specify a half-sine wave.
· Peak Acceleration (G value): The maximum acceleration value of the pulse. The typical value in the JEDEC standard is 1500G.
· Pulse Duration: The width of the acceleration pulse. The typical value in the JEDEC standard is 0.5ms.
· The G value and pulse width are related, adjusted through drop height and the material of the collision surface (e.g., damping pads).
· Drop Direction: Must cover the three mutually perpendicular axes of the product (±X, ±Y, ±Z), typically dropping multiple times on each axis (e.g., 1-3 times).
· Sample Quantity: A certain number of samples (e.g., 5-10 pcs) are usually required to achieve statistical significance.
· Monitoring and Interruption: Online, real-time electrical performance monitoring is required during testing. After each drop, immediately check for functional failure. Once a failure occurs, record the number of drops and the failure mode.
♞ Test Result Analysis and Failure Modes
♔♔ Typical Failure Modes:
· Solder Joint Cracking/Fracture: The most common form, especially for BGA and CHIP components (e.g., 0201, 0402).
· PCB Delamination/Bubbling: Especially in multilayer boards, internal copper layers separate from the PP sheet.
· PCB Microcracks: Occur in vias or surface traces.
· Component Body Fracture: Such as the fracture of ceramic capacitors (MLCC).
· ** Connector/Interface Loosening**.
♔♔ Failure Analysis Techniques:
· Visual Inspection
· X-Ray Inspection: Used to check for cracks in hidden solder joints like BGA.
· Acoustic Scanning Microscope (C-SAM): Used to detect delamination and voids within the PCB.
· Dye and Pry Test: To confirm the specific location and propagation path of solder joint cracks.
· Cross-Sectioning: Microscopic analysis of failure points, the final diagnostic method.
★ PCB Manufacturing Considerations The PCB is the foundation of the entire assembly, and its quality directly determines the upper limit of impact resistance. ☆ Material Selection (Core Material): · High Tg materials (Tg ≥ 170°C) must be used, such as FR-4 high Tg or higher performance materials (e.g., Megtron 6, ISOLA 370HR). High Tg materials maintain higher strength and rigidity under high temperatures and mechanical stress, resisting deformation and delamination. · For wireless/RF products, consider using ** Rogers materials** or hybrid lamination structures, but their brittleness may be higher and should be carefully evaluated with the board manufacturer. ☆ Copper Foil Type (Copper Type): · It is recommended to use reverse-treated copper foil (RTF) or ultra-low profile copper foil (VLP). These types of copper foil have low roughness in bonding with the substrate, providing stronger adhesion and are less likely to peel off under mechanical stress (Copper Peeling). ☆ Via Reliability: · The thickness of the via copper is critical: Strictly require an average copper thickness of ≥25μm (about 1mil) on the via walls, with the minimum point not lower than 20μm. Thin copper layers are the main reason for via fractures under stress. The board manufacturer must provide cross-section reports as proof. · Via-in-Pad Process: If the design uses via-in-pad, the electroplating filling process (VIPPO) must be adopted, with a filling rate >95%, and a flat surface; any voids are stress concentration points and are prone to cracking during drops. · Avoid Stacked Via Structures: In HDI designs, avoid blind vias directly stacked on another blind via or through-hole (Stacked Vias), and prioritize staggered vias (Staggered Vias) to reduce stress concentration risks.
☆ Surface Finish: · ENIG (Electroless Nickel Immersion Gold): The most common choice, providing a flat surface and good solderability, suitable for BGA and fine-pitch components. · ENEPIG (Electroless Nickel Palladium Immersion Gold): Offers superior corrosion resistance and wire bonding reliability compared to ENIG, making it the first choice for high-performance products, but at a higher cost. · Avoid using HASL (Hot Air Solder Leveling): Its uneven surface and high-temperature process can thermally shock the substrate, potentially affecting long-term reliability.
☆ Quality Control: · Require the board manufacturer to perform 100% flying probe testing and AOI inspection to ensure no open circuits, short circuits, or manufacturing defects. · A CPK (Process Capability Index) report can be requested to prove that their production process is statistically controlled. ★ PCBA Assembly Considerations The assembly process is where components are combined with the PCB, and its quality determines the strength of the solder joints. ☆ Solder Paste Printing: · Ensure consistency, accuracy, and thickness of solder paste printing. Use laser stencils and apply nano-coating or electro-polished stencils for fine-pitch components to ensure good release and solder paste volume.
☆ Reflow Profile: · Must be precisely optimized. Insufficient preheating may lead to inadequate solvent evaporation, resulting in voids; overheating or excessive reflow time can cause over-oxidation and weak intermetallic compound (IMC) layers. It is recommended to use nitrogen reflow ovens to reduce oxidation.
☆ Underfill:
· For large, critical BGA or CSP chips, it is strongly recommended to use underfill adhesive. Underfill effectively transfers impact stress from fragile solder joints to the entire chip area, significantly enhancing drop performance. This is one of the most effective means to improve BGA reliability.
☆ Conformal Coating / Spot Gluing: · Apply localized gluing reinforcement to large, tall components (such as electrolytic capacitors, inductors, connectors) to prevent tearing of pads due to excessive inertia during drops. · Consider using conformal coatings, but their primary function is moisture and corrosion protection, with limited mechanical reinforcement.
☆ Process Inspection: · X-Ray inspection is essential: Used to check the solder quality of hidden joints like BGA, QFN, etc., for issues like void rates, bridging, cracks, etc. It is recommended to control the void rate of BGA solder joints to below 25% (automotive electronics require stricter standards). · First article inspection and AOI: Ensure components are correctly mounted, with no incorrect, missing, or polarity-reversed issues. ★ PCB Design Recommendations “Design for Reliability” is the first and most important line of defense against drop testing. ☆ Layout: · Avoid placing heavy/tall components (such as large electrolytic capacitors, transformers, connectors) at the center or edge of the PCB. They should be placed as close to support points (such as screw pillars) as possible. · Stress-sensitive components (such as large MLCCs) should be kept away from the board edges and bending areas. The PCB will bend during drops, with maximum deformation occurring at the edges and center.
☆ Component Selection: · MLCC (Multilayer Ceramic Capacitor): · Prefer smaller sizes (e.g., 0402, 0201 are sturdier than 1206, 0805). · Choose high-reliability models (e.g., automotive grade), which typically use soft termination designs to better absorb board bending stress and prevent cracking. · BGA: Choose packages with larger ball pitch to improve soldering reliability while meeting performance requirements.
☆ Pad Design: · For MLCC, it is recommended to use Solder Mask Defined (SMD, green oil defined) pads. This can reduce stress at the solder joint ends, lowering the risk of capacitor body cracking. · Ensure pad sizes match the components to avoid oversized or undersized pads leading to tombstoning or cold solder joints.
☆ Reinforcement and Stiffness Design: · Add numerous ground stitching vias in the blank areas of the PCB. ** This increases the overall stiffness of the board, suppresses bending, and disperses local stress across the entire board. · Avoid routing fine traces in stress concentration areas like BGA corners. · PCB Thickness: Choose a slightly thicker board (e.g., 1.6mm) if structural space allows, as it has better bending resistance than ultra-thin boards (0.8mm).
☆ Structural Fit: · Work closely with mechanical engineers to ensure the PCB is securely fastened to the housing with screws, with reasonable support point layout to avoid excessive unsupported areas. · Consider using soft cushioning materials (e.g., foam) at potential contact points between the PCB and housing to absorb energy. When making requests to PCB and PCBA manufacturers, be sure to clearly state that “this product must pass the drop test according to XX standards (e.g., JEDEC JESD22-B111)” and provide specific metrics (e.g., height, number of drops). This will encourage suppliers to provide high-reliability solutions from material and manufacturing processes.
This public account will continue to update PCB/FPC design and manufacturing related content, pleasefollow to avoid missing the content you need…
If this has been helpful, please bookmark➕share➕like, thank you!
Previous exciting content:
Segmented Gold Finger Production Process and Control
PCB Impedance Matching and Software Calculation
Current/Resistance/Capacitance/Inductance Calculation
Rigid-Flex PCB Issues and Solutions
Analysis of PCB Manufacturing Defects and Causes
Common PCB Design DFM Traps
Basic Knowledge of PCB Materials (2)
Basic Knowledge of HDI (1)
Analysis of PCB Manufacturing Defects and Causes
Basic Knowledge of Back Drilling
Interpretation of IPC-4103 High-Speed and High-Frequency Materials (1)