Optimize Your PCB for Vibration, Shock and Thermal Environments

 

For mitigating PCB failure risk from mechanical shock and drop, there are a number of strategies you can use, including:

  • Excitation Reduction
Shock isolators (primarily for large electronic assemblies)
External cushioning (cell phone cases, bumpers)
Ejection of mass (battery pops out)
  • Component Level
Component selection
Flexible terminations on ceramic capacitors
Leaded parts
Bonding
Underfill/edge-bonding/staking

 

  • PCB Design
PCB thickness
Mount point locations
Talk to one of our reliability experts to learn more about failure analysis.

 

 

 

 

Optimize Your PCB Design for Thermal Environments

 

Temperature cycling is the most common cause of electronic failure. It is typically caused by a coefficient of thermal expansion (CTE) mismatch between the PCB components and the board. The greater the CTE mismatch between the components and the board, the greater the likelihood of solder joint failure.

 

 

However, failures can also be caused by localized events. For example, in automotive electronics the PCB is frequently over-constrained within an aluminum housing. The cold side of the PCB will shrink, or the hot side will expand, or both, leading to board buckling.

 

To analyze for localized events like this, you typically want to run a strain vs. strain comparison, which is an analysis of the board without housing and another analysis of the board inside the housing. This will help determine the increase in the lead strains due to the chassis/enclosure.
 

Thermal Analysis Example

The example below shows an analysis of a board without a chassis. You can see that the strain is on the BGAs.

 

Figure 7: Thermal mechanical analysis of a PCB in Ansys Sherlock (without housing)

We ran an analysis of the board in its housing, where you can see that the strains have doubled.

Figure 8

Figure 8: Thermal mechanical analysis of a PCB in Ansys Sherlock (with housing)

Table 1: Solder fatigue reliability predictions of Figure 9 in Ansys Sherlock
with 5 at-risk components

In Table 1 above, you can see the solder fatigue reliability predictions provided by Sherlock. Having the board mounted in the chassis increases the board’s failure risk. To mitigate these risks, you would need to consider a different chassis material, different PCB mounting points, adhesive staking or other component locations.

As the three examples shared here show, the most important design decisions you can make when designing your board for vibration, shock and thermal environments are:
  • Ensuring that strain-sensitive components are removed from high-strain areas.
  • Moving your mount points to alleviate stress on the board and components.
  • Carefully choosing your materials.
Simulation of each of these environmental factors will reduce test iterations and design times, and provide valuable insight into your product’s reliability and lifetime.

Contact us on +44 (0) 333 996 9930 or email: info@wilderisk.co.uk to discuss your specific needs.

 

 

 

 

Author

Theresa Duncan

Product Marketing Specialist (Sherlock and RES), Ansys

Author

Michael Blattau

Senior Consulting Engineer, Ansys