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Tombstoning
Tombstoning in the printed circuit boards (PCBs) refers to a specific type of soldering defect that can occur during the surface mount technology (SMT) assembly process. It happens when a component, typically a passive component like a resistor or capacitor, stands up vertically on one end due to uneven soldering or heating. This gives the appearance of a tombstone.
How Tombstoning Typically Occurs?
Tombstoning in printed circuit board (PCB) assembly typically occurs due to a soldering imbalance during the surface mount technology (SMT) process. Here is a step-by-step explanation of how tombstoning can happen:
Component Placement
The PCB assembly process begins with the placement of electronic components onto the PCB. This is usually done using automated pick-and-place machines. These machines precisely position the components on their designated pads.
Solder Paste Application
After component placement, solder paste is applied to the pads on the PCB. Solder paste is a mixture of tiny solder particles suspended in flux. It acts as a temporary adhesive that holds the components in place and forms the electrical connection.
Reflow Soldering
The PCB is then passed through a reflow oven. The oven has a controlled temperature profile, meaning it heats up according to a specific time-temperature curve. This causes the solder paste to melt, creating solder joints between the component leads and the PCB pads.
During this process, tombstoning can occur due to several reasons:
Uneven Heating: If one end of the component heats up faster than the other, it can cause one end to reflow and form a good solder joint while the other end lifts up.
Component Tolerance Variations: If the components have slight variations in their physical dimensions, this can lead to tombstoning.
Uneven Pad Design: If the pads on the PCB are unevenly designed or there’s a mismatch between pad size and component lead size, it can cause tombstoning.
Inadequate Solder Paste Stenciling: The application of solder paste using a stencil should be uniform. If there are variations, it can lead to tombstoning.
Reflow Profile Issues: The reflow profile, which dictates the temperature profile over time during the reflow process, should be properly set. If it’s not, it can lead to tombstoning.
By understanding all these factors, ELIPCB can take measures to prevent tombstoning during the PCB assembly process. This involves careful attention to component placement, solder paste application, and reflow soldering parameters, as well as design considerations to minimize the risk of tombstoning.
Have Tombstoning Problems in PCBA?
Is tombstoning causing delays and quality issues in your PCBA process? It’s time to regain control and put an end to this challenge.
How to Prevent Tombstoning?
Preventing tombstoning involves a combination of factors:
Design Considerations: Properly design the PCB layout, especially the pad sizes and spacing, to minimize the likelihood of tombstoning.
Stencil Quality: Ensure that the solder paste stencil is of high quality and properly aligned to ensure even paste application.
Reflow Profile Optimization: Fine-tune the reflow profile to match the specific components being used and the type of solder paste.
Component Quality Control: Use high-quality components with tight tolerances to minimize variations that can lead to tombstoning.
Manufacturing Process Control: Implement quality control measures during the assembly process to catch tombstoning early and correct it.