A customer called the Helpline with a question regarding the available tests for an electronics package that would be subjected to a high shock environment, such as a gun launch...

The  customer wanted to conduct a series of tests to validate their package design and manufacturing processes. There is no single high-g test that can replicate the dynamics of a gun launch, which makes qualification of electronic components or hardware challenging.  Two different types of launchers, which have nominally the same peak force, can produce significantly different effects on the projectile.

Commonly used high-g shock testing methods, such as centrifuge testing and high-g drop testing, have been used by a handful of test laboratories and companies.  The actual gun shock tests, such as the Ballistic Rail Gun (BRG) test and Soft Recovery Vehicle (SRV) Test, can only be done at a limited number of military facilities.  All these test methods have their pros and cons.  As a general rule of thumb, the laboratory based tests are significantly less expensive than gun launch tests at military facilities.  However, the laboratory tests do not simulate a gun launch environment as well as the actual gun shock tests.  Depending on the application requirements, the design engineers can choose a special high-g test, or a combination of high-g tests, to perform an initial screening or a complete qualification program on the test articles. 

Drop testing has been used by many companies to evaluate the effect of high-g impact on test articles.  This test can produce g-levels as high as 100,000g with very short pulse durations.  The g-force level is determined by the drop height and it is sometimes influenced by the secondary returning force.  The primary advantages are availability, cost, and ease of test.  For example, the high-g drop tester at the EMPF can simulate g-forces up to a 25,000g acceleration with less than 0.5 msec pulse duration (depending on the acceleration level).
 
After several detailed discussions with the customer, the EMPF developed a suitable test plan.  In this particular case, a series of samples per the customer’s requests and specifications were analyzed using an in-house drop tester.  Since the articles to be tested vary considerably in size and shape, the EMPF engineers worked closely with the customer to design and build the test fixtures. 

During testing, the EMPF provided high-g drop test data in the form of shock pulse curves, and also provided the digitized test data in an Excel data format.  Figure 3-1 shows a typical shock pulse generated by the drop equipment. 

Typically, the EMPF integrates high-g testing capabilities as part of a comprehensive environmental test program that includes pre-conditioning tests, accelerated aging tests, environmental tests, high impact shock tests, post high-g evaluation and examination tests, electrical tests, failure analysis, statistical data analysis, and manufacturing design and process recommendations.  The failure analysis may include X-ray examination, cross-sectioning, optical microscopy, and scanning electron microscope analysis, temperature cycling, etc.  In addition to determining the areas requiring additional structural reinforcement, more that thirty (30) different types of electrical failures have been observed. These failures include:

• Internal failures within discrete crystal oscillator packages
• Wirebond  failure due to inadequate pull strength
• Solder pad lift-off
• Improper or inadequate underfill for BGA packaged devices   
  
• Cracked capacitors
  
• Improper elastomers
  
• Circuit conductor breaks due to poor adhesion
  
• Improper encapsulation materials
  
• Poor adhesion due to inadequate cleaning or surface preparation

These tests can be used to verify that an electronics module meets the design specification, or that additional design work is needed to improve the quality of the tested modules and to assist the product insertion process into a high shock systems application.