Solder Bump Vertical Probe Cards offer a number of benefits over standard vertical buckling beam/cantilever technologies. These include a lower contact resistance, reduced contact force, and less deformation. During probing, a small horizontal movement of each probe feature across the surface of each corresponding solder bump causes a break in the non-conductive layer and thereby establishes a good electrical contact between the probe features and the solder bump.
High Contact Resistance
Contact resistance is a major challenge for wafer test. Depending on the number of solder pads and the clock rate, the con- tact resistance can impact die test measurement accuracy.
A critical factor in controlling contact resistance is maintaining the probe tip free of contamination. Accumulation of dirt on the tip increases CRES and can negatively affect the quality of the test.
As a result, used probe cards are frequently cleaned with an abrasive lapping film to lower the contact resistance. However, this process reduces the probe or tip length, which can prematurely wear out the probe card.
Managing the contact resistance of a probe during bump probing requires just enough force to break through the oxide layer protecting the bump and fresh metal to make good electrical contact. This is accomplished by adding additional travel to the z-axis, which crushes the bump and exposes fresh metal.
Reduced Contact Force
Solder Bump Vertical Probe Card can reduce the contact force required to make good electrical contacts on semiconductor devices. This can help eliminate false failures caused by excess forces that damage components below the pads.
In a first method, lateral overdrive is applied to move the probe tip along a path towards the electrical structure, as illustrated in FIG. 3A, and then scrape the probe tip along a surface of the electrical structure to engage the electrical structure mechanically and under favorable conditions.
Alternatively, the probe tip may be moved in a lateral direction away from the electrical structure, as illustrated in FIG. 7B, to avoid substantial deflection of the probe tip.
A variety of probe needles are available, including tungsten, tungsten-rhenium, Paliney (r), and beryllium-copper wire in lengths of 5 millimeters to 15 millimeters. Tips are either sharp or radiused, and are typically coated with a polymeric coating to increase needle-to-needle isolation and improve adhesion to the probe card epoxy ring.
During testing, probes can entrap contaminants that degrade the contact resistance between the bump and the metal used for electrical contact. This impedes probe performance and leads to electrical opens, speed related fails, threshold voltage, output current, etc.
The contaminants, including flux residue, build up on the surface of the bump and inhibit electrical contact. Moreover, this residue can damage the bump and the component below it. In addition, this can negatively impact test efficiency, test yield, probe card lifespan, and subsequent fabrication or assembly processes.
Another important factor that can influence the mechanical durability of probes and interconnect structures is deformation during contact with the bumps on the wafer and the substrate. The deformation of the bumps will not lead to immediate failure, but it can affect the probing efficiency and reliability of the probe.
In order to reduce deformation, we designed the Solder Bump Vertical Probe Card with a laterally compliant spring-based interposer that did not impart significant vertical force on the probe contactor substrate when in an engaged state. This reduced the lateral tenting of the contact bumps on the PCB and the probe contactor substrate, and enabled improved planarity of the contact bumps and better electrical connections with the contact bumps built on the PCB and probe contactor substrate.
Solder Bump Vertical Probe Cards are significantly longer in life than conventional probe cards. This is mainly because the probe tips are not contaminated with oxides and other contaminants as quickly. This leads to a longer hardware life and higher yields.
This also has an impact on the overall cost of test. As a result, many IC production testing facilities clean the probe cards after each flip chip test cycle to reduce contact resistance and increase yield.
However, this is not always an effective strategy. Excessive cleaning of the bumps can lead to flux residue contamination, which forms a barrier between the probe needle and the bump, preventing electrical contact. This contaminant can negatively impact the performance of high-frequency devices. It is important to understand the cause of this contamination and establish procedures for proper removal. This will prevent this issue from reoccurring and increase the lifetime of the probing tool. This will also improve the test process and throughput.