KJR-4013E is a flexible, moisture-cure silicone most often used as junction-coating resins in the manufacture of diodes. KJR-651E, KJR-655E and KJR-657E are rigid thermoset polyimide-silicones used as junction coating resins in the manufacture of higher power diodes and thyristors. Both are used due to their excellent adhesion to epoxy molding compounds (EMC), high humidity resistance, and excellent volume resistivity and dielectric breakdown properties.

To be able to conduct failure analysis, customers have asked if there is a process to remove the cured silicone / polyimide-silicone from the diodes and/or thyristors (decap).

One recommendation is to use sulphuric acid (H2SO4) which can normally clearly strip organic compounds.  Nitric acid (HNO3) is another option.  If the dissolving rate is slow, adding heat to the process helps very much.  Of course, for either of these processes, a fume hood is necessary all the time.

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Our standard cure schedule recommendation for the Shin-Etsu KJR-651E is as follows:
150°C for 1hr + 200°C for 1hr + 250°C for 4 hrs

This is the minimum cycle required to drive out the solvents and get good cure characteristics.  However, this is only a recommendation; a good starting point.

Some manufacturers use a hotter, longer cure cycle such as :
110°C for 1hr + 200°C for 1hr + 250°C for 8hrs + 300°C for 4hrs + 380°C for 30 mins.

It has been determined by them that this is optimum cure cycle required to maximize performance and minimize current leak.  This has been confirmed by several customers who measure the gate leakage or leakage current at the maximum temperature of the junction test when the reverse voltage is applied.

These two cure conditions likely (but not definitely) represent the two extremes in cure conditions that customer could use to test the performance of their parts – especially to test for gate leakage at high temperatures.  Though the higher temperature may give better gate leakage parameters, the standard may give better adhesion characteristics.  Either way, these parameters ultimately need to be tested by the customer, ultimately testing both the adhesion characteristics and leakage current at the max temperature of the junction test.

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