TECHNICAL PAPER

Ruggedization Study

Commercial Off-The-Shelf IC Devices Ruggedized for Thermal Cycling

Introducing a Cost-Effective Solution to Ruggedize COTS Components

For critical applications that demand highly customized modules, system architects often face the challenge of high costs due to small batch production. However, we have developed an innovative and cost-effective approach to transform commodity components into high-reliability modules capable of withstanding frequent and large temperature excursions.

3 Configurations Compared

In a recent demonstration, we purchased 90 commercial off-the-shelf fine pitch BGA (FBGA) RAM modules and arranged them into three experimental configurations. The first configuration of modules was mounted directly on custom test boards, accompanied by an FPGA programmed to test the continuity of the memory module’s solder balls during thermal cycling. The second configuration underwent re-balling with Sn63/Pb37 solder before being mounted on identical test boards. The final configuration of modules was repackaged on custom 0.8 mm BGA interposer substrates, with balls aligned beneath the original module’s balls and overmolded for added protection.
Package Variant Description
Config. 1 Micron MT40A512M16LY-062E IT:E (COTS with SAC302 Balls)
Config. 2 Config. 1 Re-balled with Eutectic SN63/Pb37 balls
Config. 3 Config. 1 Repackaged as Overmolded 0.8mm Pitch Interposer with Eutectic Sn/Pb37 Balls

The experiment involved subjecting the different module configurations to thermal cycling tests. The results clearly showed the superiority of the repackaged module (configuration 3), which exhibited a 2.5-fold improvement in thermal cycling survivability compared to the commercial off-the-shelf configuration. The failures in the non-overmolded modules (configurations 1 and 2) were mainly attributed to solder ball failures near the corners of the die. However, with the repackaged module, failures were largely restricted to the external solder balls connecting the component to the test board, while the solder balls between the original device and the interposer remained intact.

Technical Paper

COTS DRAM Modules Ruggedized with Overmolding for Improved Thermal Cycling

Configurations 1 & 2

Configuration 1: COTS Micron component (SAC302 solder balls) and Configuration 2: Micron component with SAC302 balls replaced with eutectic tin/lead balls

Configuration 3

Configuration 3: The COTS Micron part repackaged on an interposer having the same 0.8 mm pitch, eutectic tin/lead balls, and overmolded

This study highlights the significant benefits of our simple repackaging approach, resulting in a substantial improvement in thermal cycling survivability. The technique can be applied to various commercial BGA type devices, offering a low-cost alternative to custom-designed bare die package assemblies. Based on these findings, further enhancements can be achieved by redistributing frequently failing nets away from high-stress solder balls, thus extending the lifespan of the repackaged parts and reducing maintenance costs in systems exposed to extreme temperature excursions.

Choose our cost-effective ruggedization solution and ensure the reliability and durability of your critical applications. Contact us today to learn more about transforming commodity components into ruggedized, high-reliability components.

Pictured (above): The measured cumulative failures for each of our three component populations as a function of the number of thermal cycles is plotted (above left). The Configuration 1 COTS micron component (blue), Configuration 2 eutectic re-balled Micron component (red), and the Configuration 3 repackaged component (green). A two parameter Weibull continuous distribution function is fit to each component’s data. The shaded areas represent the 95% confidence band for each data set.

Also plotted (above right) are the Weibull probability density functions for each of the populations based on the fitted parameters.

Pictured (left):
A typical eutectic solder ball failure in the Configuration 2 component. These failures are most prevalent in balls located near the corners of the of the die. The fractures are located on the lower inside and upper outside edge of the solder ball. This indicates that the highest stresses occurred during the contracted stage (cool) of the thermal cycle. The Configuration 1 component showed similar failures.

Technical Paper

COTS DRAM Modules Ruggedized with Overmolding for Improved Thermal Cycling