tombstoning

**Tombstoning** is the **reflow defect where one end of a small chip component lifts from the PCB and stands upright due to unbalanced wetting forces** - it is a common challenge for small passive components in high-density SMT assemblies. **What Is Tombstoning?** - **Definition**: Asymmetric solder wetting force rotates the component before both ends fully settle. - **Typical Components**: Most frequent in small resistors and capacitors such as 0402 and below. - **Primary Causes**: Pad temperature imbalance, unequal paste volume, and placement offset are common triggers. - **Detection**: AOI readily detects tombstoned parts after reflow. **Why Tombstoning Matters** - **Functional Failure**: One terminal disconnect leads to open-circuit behavior. - **Yield Impact**: Tombstones can become major contributors in miniaturized product lines. - **Process Sensitivity**: Defect rate reflects combined print, placement, and thermal-profile balance. - **Rework Cost**: Manual correction increases labor and introduces handling risk. - **Scalability**: Tombstoning risk rises as passive size decreases and pitch density increases. **How It Is Used in Practice** - **Pad Symmetry**: Design matched pad geometry and thermal relief on both terminals. - **Paste Balance**: Control aperture design and print consistency to equalize solder volume. - **Profile Tuning**: Use reflow ramps that reduce wetting-force imbalance during melt onset. Tombstoning is **a classic passive-component reflow imbalance defect** - tombstoning control requires synchronized optimization of footprint symmetry, paste deposition, and thermal uniformity.