BGA Testsockel

Making Ball Grid Array Sockets You Can Count On Ten years ago the high pin count market was relegated to PGA and CGA devices. Today BGA devices rule this market. There are plenty of challenges associated with high pin count BGA devices, but your test socket should not be one of them. In order to make sure it is not, we utilize a variety of materials and design methodologies. As I/Os creep up into the thousands, structural strength can quickly become a concern. Our designs are analyzed to address the pressure concerns (i.e., 1.2 oz per pin x 2000 pins = 150 lbs in a 60 mm square) while still meeting manufacturability considerations.

Floating Nests As with any socket, contact between the spring probe and the device lead is critical for high pass yields. In BGA devices this is compounded by the extension of a ball from the substrate which must be aligned before contacting the spring probes. By simply aligning off the substrate, a device can be introduced to the spring probe in a manner in which the balls are not properly aligned. This often leads to ball shearing or probe damage. In order to eliminate this possibility, we often uses a floating nest to align the balls before contacting the probes. This method, whether using a window frame or one ball/one hole nest, allows the device and balls to align in a nest that “floats” on springs above the probe tips. Once aligned the device can then be introduced to the spring probes without the worry of ball or probe damage.

Lead Free Solder Balls
The move to lead-free products has put as much strain on the BGA market as any other type of device. Some of the major points of interest are adhesion challenges, TCE mismatch, and splintering. When testing a BGA device, no matter what the percentages are in the SnAgCu solderball, penetration is critical. We have optimized our Endura Series to address these new challenges.
The benefits are numerous:

• Plating is harder and more resistive to solder.
• Harder base material provides greater probe life due to less tip wear.
• The spring force can be increased by almost 30%.
• Reduced 4-point crown is available for smaller featured parts.

The Importance of Compliance
One of the primary responsibilities of any production test engineer is the initial tweaking of the test setup in order to make sure 5 to 10 separate components work together. The test socket is often the one component in that list that has the ability to maximize compliance without sacrificing performance. Without this compliance, minute variations in set-up or coplanarity can mean substandard pass rates. This idea is one of the primary driving forces behind our Compliance Plus Probe, the next generation of our chip scale probes. The Compliance Plus Probe marks the continual evolution of the ground-breaking Endura probe line. The increased travel, or compliance, offered in the Compliance Plus Probe has been very beneficial in the high speed, low margin of error world of BGA testing.