FAILURE ANALYSIS ON HIGH POWER SEMICONDUCTORS

Poseico may perform a failure analysis on failed devices (press-pack or insulated module devices) in order to evaluate the potential failure causes occurred during the device operation on field. Thanks to its own database, Poseico may provide a quick and deep evaluation of failure conditions and perform specific laboratory tests (mechanical and electrical) to help the Customer to mitigate potential wrong working conditions of the final application.

AUTHENTICITY CHECKS

Counterfeit goods span across multiple industries including the Power Electronics one. Poseico is fighting against this unpolite competition and it offers a complete service in order to analyze if semiconductors, branded Poseico or other, are original or fake.

MOUNTING RECOMMENDATIONS

In order to ensure effective cooling, good current conduction and reliability, in the assembly of Power Semiconductors, it’s important to observe some recommendations with a particular focus on heatsink preparation and clamping system. The recommended procedure is reported below:

USING BAR CLAMPING SYSTEM

• - clean the mounting area (a) of both heatsinks before with “abrasive rubber” and than with alcohol.
• - clean the mounting surfaces of the semiconductor with alcohol.
• - apply a thin film of mounting grease (b) on both mounting surfaces of the heatsinks.
• - put the semiconductor between the two heatsinks and rotate it to spread the contact grease.

CAUTION: each guide pin should be located in the center hole.

• - pre-assemble the clamp housing if necessary
• - place the pre-assembled portion of the clamp through the heatsink and the semiconductor assembly.
• - place over the upper heatsink the second part of the clamp, equipped with its spring system and hardware parts.
• - tighten by “fingers” the screws and put all the assembly in position.

CAUTION: all the surfaces must be parallel before tightening.

• - tighten the screws half a turn until the pressure indicating system shows that the required pressure has been achieved.

USING BOX CLAMPING SYSTEM

• - clean the mounting area (a) of both heatsinks before with “abrasive rubber” and than with alcohol.
• - clean the mounting surfaces of the semiconductor with alcohol.
• - apply a thin firm of mounting grease (b) on the surfaces of the device.
• - put the box clamp over the device ensuring that the pins are correctly located.
• - put the square steel plate over the central rod, putting bolts through the clamp whilst holding it firmly in place.
• - screw the bolts “finger tight” then alternatively, clockwise, half a turn until the box touches the heatsink all the way round.

CAUTION: use a torque wrench to apply the right clamping force.

• (a) recommended tolerances over the device mounting area: flatness 30 micron, roughness 2 micron
• (b) recommended mounting grease: contactal hpg Note: before mounting the assembly, a leakage test must be performed to verify the electrical integrity.

Maximum allowable average current

In this catalogue the average current ratings are mostly specified for temperatures of: Th = 55°C. Tc = 85°C at 180° sine wave. For other temperatures, the current can be calculated using the following formulas applicable up to 400 Hz:

• I(AV) = IT(AV) for thyristors, IF(AV) for diodes
• Vo = VT(TO) for thyristors, VF(TO) for diodes
• T = Tc or Th
• Rth = Rth(j - c) or Rth(j - h)
• r = rT for thyristors, rF for diodes
• K = 1 for direct current
• K = (π /2) for 180° sine wave
• K = √3 for 120° rectangular wave
• K = √2 for 160° rectangular wave