Optocoupler Failures

Gideon Analytical Laboratories received two failed photocouplers for failure analysis. These photocouplers feature a high isolation voltage, high-speed switching, and high collector to emitter voltage. They are used in many types of applications, including power supply, telephones, and fax machines. The optocoupler was electrically tested; there was a short on both input diodes. The goal was to determine the cause of this failure.

After curve trace tests were performed, both failed devices were immersed in a low surface tension dye penetrant This is a modified Mil-Std 1014.2 with alterations reflecting current processing. After several other tests, these were confirmed as hard shorts. Any dye penetration constitutes a failure and demonstrates that moisture could have ingress the package of these failures.

The diode is encapsulated in silicone, which is hygroscopic and acts as a buffer during thermal movement to prevent the diode sheering from the lead frame. Pictured at the top left is of the top looking down. This picture was taken using a black light and inspecting for the fluorescent dye (green) to indicate penetration. The picture at the top right is of the dye; it had corrosion near the bond band. SEM-EDS analysis was performed and micrographs were taken up to 4500X.

Gideon Analytical Laboratories came to some important conclusions. These failures were non-recoverable failures. The dye penetration test demonstrates these opts are very susceptible to moisture ingress. The migration of silver on the two of the diode surface indicates that moisture and voltage were present within the package. The silver is forming a connection bridge between the anode and cathode and either shorting or causing excessive leakage current.

The presence of chloride causes corrosion as shown in above micrograph. The concept of having chloride on the die indicates it entered in with copious amounts of moisture.

Gideon Analytical Laboratories solved another problem, illuminating light on the cause of why these devices were failing. If electronics companies are experiencing any type of failures in the manufacturing or in the application of their devices, they can rest assured that Gideon Analytical Laboratories is here to help. Failure analysis can provide accurate and candid results that save companies enormous amounts of time and money.