Enhancing Reliability With Copper Lead Frames

ADVANTAGES & BENEFITS

Superior thermal conductivity improvement: 170 W/m*K vs. 14 W/m*K (a 12X difference).
Θ ja and jc characteristics provide up to 3.8X advantage of heat dissipation capability versus parts with alloy 42 lead frames.
Heat dissipated from the die faster makes it run cooler leading to longer life.
Solder joint reliability vastly improved.

CTE of Copper (17 ppm/ °C), matches the CTE of Typical FR4 PWBs (15-17 ppm/ °C)
CTE of Alloy 42 (5 ppm/ °C), mismatch to CTE of FR4 PWBs (15-17 ppm/ °C)

RoHS Version (NiPdAu plating)

Most preferred for elimination of risk for whisker growth.

The use of copper lead frames inherently allow for better solder joint reliability, tin whisker prevention and better thermal dissipation. These are three big factors in overall system reliability over time.

Better Solder Joint Reliability

Many systems are expected to operate reliably over broad temperature variations spanning the industrial (-40°C to +85°C) and military (-55°C to +125°C) temperature ranges. System problems can be caused by the mismatch of thermal coefficients of all system components. Better solder joint reliability is obtained since the copper lead frame is more flexible, and the CTE of the copper lead frame is better matched with that of typical FR4 PWBs, than that of Alloy 42. Repeated thermal cycles over a period of time can take a toll on solder joints, causing cracks and intermittent connections where expansion and contraction of the lead frame is at a different rate than the FR4 PWB that it is attached to.

Whisker Prevention

The RoHS version of this copper lead frame, with its' NiPdAu (Nickel-Palladium-Gold) plating, eliminates the risk of tin whiskers. Microscopic whiskers can grow on a parts' pins than have tin content in the plating. Traditionally Alloy 42 lead frames have a Sn or PbSn plating. This plating containing tin, along with certain environmental conditions can cause these whiskers to grow. Their growth may extend to form a bridge with another pin on the device, or the whisker may break off and cause a short circuit or even an explosive power surge on the board. The organization, iNEMI (International Electronics Manufacturing Initiative) lists the NiPdAu lead plating as the most preferred for elimination of risk for whiskers.

Better Thermal Dissipation

Because copper has a 10X to 12X improvement in thermal conductivity vs. Alloy 42, and since Θ ja and Θ jc characteristics of copper provide up to 3.8X advantage over Alloy 42, more efficient thermal dissipation is the result. This translates to better heat dissipated away from the chip through the lead frame and PWB, thus extending the useful life of the die by reducing die junction temperature. Therefore less heat stress remains in the device, which is a leading cause of non-mechanical failure in a long life application.