Mechanical Reliability  test 

Introduction

Mechanical reliability tests are essential for testing the electronic products under different mechanical stresses.

Background

The passing criteria for mechanical reliability is to ensure no noticeable cosmetic damage, no noticeable mechanical damage , no electrical failure, and lastly no product functional failure.

Overview

Vibration

• • This test applies high frequency vibration (10 to 500Hz) on the electronic product in each of axial directions (x, y, and z) to test if the product does not become loose (i.e no excessive gap size observed in the seams of the device) and product is functional.

  • An common acceptance criteria will no noticeable mechanical damage, and no failure in both mechanical and electrical functions.

Drop

• • This tests drops the electronic product from a defined reasonable height and see if the electronic products is still functional.

  • Typically drop test is performed at four sides and two surfaces, so it's a total of 6 orientations at a height roughly 0.8 to 1m above surface from consumer hardware device.

  • An example of acceptance criteria is no mechanical and electrical functional failures and electrical specification is met.

Connector

• • Cycling Test: Repeatedly pull the cable overmold with device under test fixed in place(e.g. pull from HDMI Cable  in order to disengage HDMI plug from device's HDMI receptacle)

    • An example of acceptance criteria is that the device withstand 100 times of repeated pulls/yanks, and at the end of the stress test, the the connector can still be inserted with retention force not deviate too much from original one, and it also meets the minimum retention force specified by the connector vendor. 

  • Side Load test: Apply a perpendicular force centered on connector body with plug inserted in the device under test. This allows situation where an external forced applied on the connectors while inserted to the receptacle such as a book fall on top of the connector or the DUT is placed tightly in a space where object interference an happen.

    • An example test would apply 2-6 kgf (1 kgf = 9.8N)  50 to 100 times to each orientation of the connector using a cylindrical rod.

    • An example of acceptance criteria is that there is no mechanical failure that results in functional failure and also meets connector electrical specification (i.e USB data transmission works reliably).

  • Kick test: This simulates the scenario where device fall from a fixed/unfixed location but the cable is still attached between two devices (such as Streaming Stick with TV HDMI in or power cable fall and yank the device off the table). The test the retention force of these mating connectors

  • An example of acceptance criteria is that the cable remains mated with the device and the change in retention force does not deviate too much from the original state and also meets minimum retention force. Also there is no electrical and mechanical function failures.

Tumbling

• • This test is conducted by placing the electronic device inside a long mechanical square tube with various lengths. Then this tube is rotated.

  • Application: 

    • A portable device generally goes through this test.

Summary & Conclusion

• Vibration tests the mechanical and electrical components structural integrity under high frequencies in 3 product axis.

• Drop tests the the mechanical and electrical components structural integrity under a predefined height.

• Connector tests mechanical integrity of the connector and receptacle under different mechanical stress such as cable yank and connector side load test.

• Tumbling tests the mechanical and electrical components structural integrity under repeatedly tumbling with different distances.

Mechanical readabilities is essential for device that is portable and have connectors that are used often. An system design engineer will pick mechanical parts that has the best rigidity and use the under-fill and potting on electrical components on the PCB to improve product reliability under vibration and drop tests.