Modern circuit boards are
becoming dense, which gives rise to the demand for smart and compact electronic
components. The use of surface mount components is increasing rapidly, and
their size is shrinking so that maximum SMT components can be accommodated in the
circuit board. The soldering process of these small components can sometimes leave
a defect known as “Tombstoning”.&苍产蝉辫;
Tombstoning is a defect in PCB that
occurs during the soldering process when one end of SMT components, like
resistors or capacitors, is left unsoldered. This causes the unsoldered end to stand
upright or inclined. This is why it is called tombstoning. This tombstoning
defect, also known as the Manhattan effect, creates an open circuit in the PCB,
resulting in device malfunction. The rework requires additional cost and decreases
the reliability of the PCB. This article will help you understand the
fundamentals of tombstoning, its causes and effects, and how to avoid
tombstoning in your PCB.
What is a Tombstoning PCB?
Tombstoning is a well-known defect in printed circuit board
assembly. During the PCB soldering process of SMT components like resistors and
capacitors, sometimes one end of these components is left unsoldered, and it stands
upright or erect. This defect is known as tombstoning. The tombstoning effect
is highly undesirable in circuit boards as it creates an open circuit that
results in board failure or malfunction.
The effort can be made to rectify the tombstoning defect using
rework soldering. But it requires additional cost, resources, and decreases the
overall reliability of the circuit board. This is because the rework requires
heating to solder the unsoldered point of the SMT component. Therefore,
tombstoning is dangerous for circuit boards, and it is important to avoid
tombstoning.
Factors Leading to Tombstoning PCBs
The manufacturing process of SMT, particularly the reflow oven
process, is a major contributing factor leading to tombstoning defects. Some
other factors can potentially contribute to the tombstoning defect in the PCB.
1. Pad Size: Generally,
large pad sizes of SMT components like resistors and capacitors can potentially
lead to tombstone defects.
2. Components
Geometry: It has
also been observed that the printed circuit board pad size and geometry are contributing
factors in tombstoning defects in PCBs.
3. Excessive Solder Paste: Another tombstoning defect in PCB is the
excessive solder paste present between the pads of SMT components.
4. Irregular pad sizes: The inconsistent pad size of the component
in the designer's library and the actual pad size result in a tombstoning
defect in the reflow soldering process. This is because the larger the pad
size, the larger the solder paste, increasing rotational torque when the solder
paste becomes liquid.
5. Incorrect use of
solder paste: When the solder paste does not melt
at the same time at both ends of an SMT component, one end of the component pulls
upward. This causes the tombstoning defect.
6. Use of irregular
shape components: The components having different
shapes at both ends are more likely to encounter a tombstoning defect. This is
because the surface tension of the molten solder affects the component
differently depending on its orientation. As a result, one end of the component
will lift upward and create a tombstoning effect.
7. Incorrect component
placement: If
the components are not placed exactly at an angle or placed inconsistently as compared
to their pad locations. This creates an imbalance and results in tombstoning in
PCB.
8. Inefficient use
of Reflow Oven: Another
important factor leading to the tombstoning effect is a poorly controlled
reflow profile. Uneven heating leads to tombstoning in PCB.
The Impact of Tombstoning
The tombstoning impacts the device's
performance, reliability, and functionality. The impacts of tombstoning, when encountered,
contribute to：
1. Increase Product
Cost: Tombstoning
defect, when encountered in a PCB manufacturing industry, increases the cost, increases
production time, and consumes extra resources.
2. PCB Reliability: Tombstoning requires rework, and
it requires heating the components that are left unsoldered. This decreases the
reliability and functionality of the PCB.
3. Component Damage: The heating required to solder
the components that are left may damage the components due to the excessive
heat or multiple cycles of heating.
4. Compromise
Performance: Sometimes, tombstoning may not damage or compromise the entire functionality of
the PCB but may compromise the performance of the PCB.
5. Increase
Production Cost: The PCBs that encounter tombstoning require extra cost and therefore increase
the overall production cost of the project.
6. Non-Compliance: Tombstoning in PCBs, if left
unchecked, can bring serious consequences. The device may fail the quality
standards, resulting in an increase in product time to market.
How to Avoid a Tombstoning PCB Defect
Tombstoning
in PCB is a major concern for ensuring the reliability of PCB. By applying the
best practices, it is possible to avoid or eliminate the risk of tombstoning.
Some of the best practices to avoid tombstoning are listed.
1. Thermal Profile: It is recommended to establish a
comprehensive and accurate thermal profile during reflow soldering so that heat
is distributed uniformly, avoiding the risk of encountering tombstoning in the PCB.
2. Accurate Pad
Dimension: Always
use the accurate pad dimensions to avoid the tombstoning defect. The pad is greater
than the actual size or smaller than the actual size, creating the tombstone in
PCB. The designer must ensure the use of accurate dimensions of components.
3. Correct Component
Orientation: The
incorrect orientation of components is another root cause of tombstoning in
PCB. The components' orientation should always be similar to avoid uneven
solder paste distribution during the reflow oven.
4. Components
Terminal Size: A
good practice to avoid tombstoning in PCB is to use components with balanced
terminal sizes.
5. Quality Control
Measures: Industries with good quality control setups are less likely to encounter
tombstoning defects in their PCBs. The quality control ensures that the solder paste
distribution is uniform and as per the quality standards to avoid having any
tombstoning defects.
PCBasic Prevents Tombstoning with Rigorous Quality Control
PCBasic has created its image in the PCBA manufacturing industry
with its extensive and rigorous quality control measures. The company not only enhances
its capabilities over time but is also able to meet the customers' expectations
with its guaranteed and quality-assured product. PCBasic's comprehensive
quality control system ensures that no tombstoning-like defects may happen.
1. PCBasic’蝉 advanced machines, e.g., Automated Optical Inspection (AOI), and
X-ray inspection ensure that tombstoning in PCB should never happen.
2. PCBasic quality control plays a critical role in preventing
tombstoning from occurring. Quality control has a key role in the reflow
soldering process and uniform distribution of solder paste that prevents the
tombstoning defect in PCBs.
3. PCBasic has a streamlined quality control system to ensure that components
with the exact pad dimension have been used, preventing chances of tombstoning
in PCB.
4. The smart and efficient system of PCBasic helps the technical
operators to identify and correct errors like tombstoning in PCB if it ever happens.
This also helps the engineers to avoid such mistakes in the future.
5. PCBasic has a rigorous component quality control mechanism that decreases
the chance of using the wrong components, resulting in the prevention of
tombstoning defects.
6. PCBasic has an and quality system
that ensures the quality check at every step of the production cycle, resulting
in the least occurrence of defects like tombstoning.
7. The expert quality control team of PCBasic ensures that reflow
profiles are consistent. This prevents the chance of uneven heating and
component damage, which reduces the risk of tombstoning in PCB.
Conclusion
In modern electronic designs,
product reliability and performance are critical parameters. By following the
techniques and methods to reduce tombstoning defects, PCB manufacturing
companies can reduce product costs, enhance efficiency, and achieve excellence.
PCB tombstoning is a defect in PCB assembly, and steps must be taken to avoid it.
In PCB tombstoning, the one end of the SMT component is left unsoldered and
stands upright. The tombstoning, if not rectified in a timely, can reduce the product's
reliability and functionality.
Therefore, understanding
tombstoning, its impact on product performance, and the factors leading to its
cause is important for engineers so that they can rectify them in a timely
manner and make informed decisions. Strict quality measures must be adopted in
order to eliminate or reduce the cause of tombstoning in PCBA manufacturing. By
implementing the quality control measures, tombstoning can be reduced to a minimum,
which results in enhancing the product’蝉 reliability, efficiency, and overall
performance.
