Integrated Analysis of Electronics Based on Random Vibration

and Thermal Cycling Constraints

Valeriy Khaldarov

Electronic Components Reliability Analysis

Mesa, AZ

vkbgoog@gmail.com

Abstract – There is a connection between the size of the

printed circuit board (PCB), its natural frequency and the

life of solder joints for a through-hole-mounted

component. An integrated software package, ASONIKA,

can quickly simulate electronics and chips subjected to

complex thermal and mechanical influences. Knowing

this general guideline allows for a combined thermal and

mechanical concept to move forward. Trade studies of

PCB size and appropriate parameters for vibration

isolators can produce a design that will satisfy the loads

experienced in random vibration and thermal cycling

environment. This saves time and money for the

electronic equipment designer and manufacturer.

I. INTRODUCTION

There must be a “Rule-of-Thumb” for designing electronic

equipment parameters based on vibration and thermal

environment influences the electronics must operate

under. By applying Miner’s cumulative damage ratio,

where

�� ���

���

��

���

��

���⋯ 1.0, (1)

and using ASONIKA-V subsystem, trade studies of PCB size

and vibration isolator parameters are easy to identify.

II. TRADE STUDY

We review an example described by Steinberg [1]. Figure 1

shows geometry of a polyimide glass PCB with a through-

hole-mounted hybrid component designed and used for

monitoring performance of a delivery truck combustion

engine located inside the engine compartment.

Figure 1: Dimensions (in inches) of the PCB and its

through-hole-mounted hybrid component

The electronics will be expected to go through and

withstand random vibrations from an environmental stress

screening (ESS), city, and highway driving. Power spectral

density values and their durations are shown in Figure

2(a).

Figure 2: Transient stresses experienced by the PCB and

its component due to random vibration and thermal

cycling.

In addition, the electronics will need to withstand thermal

stresses due to thermal cycling conditions experienced

during ESS, city, highway driving, and storage

environments. The expected temperature differences and

their respective number of thermal cycles are given in

Figure 2(b).

III. ASSUMPTIONS

We make the following assumptions with respect to

calculations:

A. There are equal number of failures in the lead wires

and solder joints from random vibration.

B. Solder joint height and PCB thickness are the same.

Since the differences of the coefficients of thermal

expansion of a through-hole component and the PCB

can produce overturning moments in the wires that

lead to shear tear-out in solder joints (see Figure 3), we

attribute PCB thickness as a variable parameter to

thermal cycling fatigue.

Figure 3: Solder shear tear out due to mismatch of

coefficients of thermal expansion for a through-hole

component and the PCB [1].

IV. RESULTS

Figure 4(a) shows a typical “Damage-Boundary” diagram,

where the x-axis represents PCB thickness, y-axis --

resonance frequency of the PCB,

Figure 4: Fatigue cycle ratio values with respect to

resonance frequencies of the PCB and thickness.

and the lines (referred to as Critical Frequency and Critical

PCB Thickness) -- separation of damage and no damage

regions.

We can see that only blue and purple regions can satisfy

the inequality condition specified in Equation (1).

Furthermore, in the context of Stress Margin Analysis [2]

only the blue region will satisfy six sigma design

robustness requirement.

Figure 4(b) and (c) show the response breakdown to each

influence with respect to either PCB thickness or natural

frequency. From Figure 4(b) we see that PCB thickness can

significantly change fatigue ratio values between 0.06 and

0.10 inches; while from Figure 4(c) we can infer that this

ratio will not change much at around 160 hertz for the

PCB. To achieve this natural frequency, we use ASONIKA-V

subsystem to identify appropriate parameters of vibration

isolators for the PCB.

Table 1 lists two types of vibration isolators taken from

ASONIKA database where the second type exceeds rigidity

values of the first by a factor of about 2.5.

Table 1: Rigidity values for

(a) type I and (b) type II

vibration isolators

Figure 5(a) and (b) show system response subjected to

highway driving conditions with natural frequency of

about 100 Hz for type I and 160 Hz for type II vibration

isolators along the x and y axes. Figure 5(c) shows that the

natural frequency of type II vibration isolators stays at

about 160 Hz when the electronics are subjected to city

driving conditions.

Figure 5: System response of (a) type I, (b) type II

vibration isolators subjected to highway driving

conditions, and (c) type II vibration isolators subjected to

city driving conditions.

We can use the following calculations [3] to double check

our results.

�� �����

��� ∗ � ∗ � ∗ ��

9.8

where �� = 160 Hz, selected system natural frequency

� = 6 in, width of the PCB

� = 8 in, length of the PCB

� = 0.075 in, PCB thickness

� = 0.0578 lb/in3, density of the PCB

�� ��160���6 ∗ 8 ∗ 0.075 ∗ 0.0578�

9.8= 543.6 �"/$%

Since 4 isolators will be used to support the system, the

required rigidity value of each isolator becomes

�� =543.6

4= 135.3 �"/$%/$&'�()'*

Since this calculated rigidity value is less then ones shown

in Table 1(b) for x and y axes, we conclude that the

parameters listed for vibration isolators of the second type

are more appropriate for highway and driving conditions

given in Figure 2(a).

V. CONCLUSIONS

Calculating Miner’s cumulative damage ratio for an

electronic equipment operating under particular

environmental conditions allows easy access to vibration

isolator parameters in ASONIKA-V subsystem. Once the

relationship between PCB size and natural frequency is

known, the design has a robust concept. It is now ready for

detailed design by various experts.

REFERENCES

[1] D. S. Steinberg, Preventing Thermal Cycling

and Vibration Failures in Electronic

Equipment, John Wiley & Sons, 2001.

[2] N. Pascoe, Reliability Technology: Principles

and Practice of Failure Prevention in

Electronic Systems, John Wiley & Sons,

2011.

[3] LORD, "Aerospace and Defense Isolator

Catalog," [Online]. Available:

http://www.lord.com/products-and-

solutions/vibration-and-motion-

control/aerospace-and-defense. [Accessed 4

February 2016].

[4] A. Mangroli and K. Vasoya, "Optimizing

thermal and mechanical performance in

PCBs," Global SMT & Packaging, pp. 10-12,

December, 2007.