BGA Packages

Challenges of and Solutions for Contacting Ball Grid Array Devices

  • Features

    • area arrays such as BGAs provide the highest contact density of any package type
    • high ball counts can accommodate the massive quantity of I/O paths required for highly integrated devices
    • the high ball counts also allow significant quantities of power and ground paths, both to accommodate high power requirements and to reduce inductance for clean power delivery
  • Contacting Challenges

    • high ball counts
    • fine pitches (and getting finer)
    • planarity issues
    • alignment
    • lading two probes for Kelvin applications
    • making good contact without creating solderability issues
  • Probe and Contactor Features for BGA Packages

    • super-sharp tips
    • lower-force probes
    • large compliance windows
    • fine-pitch Kelvin probes
    • full-co-axial signal paths
    • dimensionally stable contact materials
    • floating alignment plates
    • mechanical simulation capabilities

BGA Packages

Ball Grid Array packages have been in use for over twenty years now, yet the numbers are still growing. It is a very versatile package that offers many advantages in terms of contact density and overall contact count. Not only do the high-ball-count BGAs provide numerous I/O paths for highly integrated devices, they also can improve current-delivery capability and voltage stability for high-power devices by providing massively parallel power and ground paths.

The BGA is also supports miniaturization as the package of choice for WLCSP devices.

Challenges

BGA contacting presents a unique set of challenges. High ball count BGAs are also often physically large packages that suffer from poor planarity. WLCSP devices are usually tested in parallel. In both cases, the high number of probe makes socket or probehead planarity more difficult. And more probes in the contactor means more force to actuate it. In some cases the force can exceed the capability of the handler.

Alignment to the spherical solder balls is challenging, and more so because the apex should not be touched to maintain solderability. Making Kelvin contact means aligning two independent probes – double the challenge.

Addressing the Challenges

Xcerra contactors employ rigid materials with low hygroscopy to maintain their dimensional stability. The spring probes have a high compliance window to accommodate package planarity variations as well as some contactor bowing. Simulation is useful to predict the contactor bowing so it can be alleviated. Xcerra probes can make good contact at lower forces thanks to super-sharp tips.

Alignment of singulated packages is accomplished with a floating alignment plate. This feature provides alignment directly to the targets, so the ball apex can be avoided. The FAP also protects the probe tips in the harsh environment of package test.

Finer-pitch BGAs mean smaller Kelvin probes, and Xcerra has probes to support true Kelvin at 0.4 mm pitch.