A probe card is essentially an interface or a board that is used to perform wafer test for a semiconductor wafer. It is used to connect to the integrated circuits located on a wafer to the ATE (Automated Test Equipment) in order to test their electrical parameters and performance before they are manufactured and shipped out.
Photo: Probe Card (credit: Synergie-CAD)
To make the process simpler, consider the process of semiconductor manufacturing. During silicon production, several integrated circuits are located onto a semiconductor wafer. This wafer is then diced and packaged and shipped out. However, before the packaging is performed, the circuits need to be checked for their functionality. This electrical test is conducted with the help of a probe card. The probe card is mounted onto a prober and then connected to a tester in order to create an electrical path between the semiconductor wafer and the tester. The probe card then uses its metallic elements or needles to connect with the pads of the integrated circuit chips on the wafer and deliver the electrical information and relevant parameters that need to be tested.
As such, the prober or the probe card itself can be described as the head of the tester that has to be connected to the metal bumps or pads on the wafer in order to be able to transmit the electrical data. The prober is used to dock the probe card and then lower it onto the wafer until the needles or bumps connect and the flow of current established between the connection. Some movement of the probe needles as they make contact with the wafer’s metal bumps is necessary in order to scrub off the oxide layer and be able to connect to the metal surface underneath.
There are essentially three kinds of tests that are performed using a probe card including a DC test, an AC test, as well as a function test.
DC Test
A DC test calls for the checking of the presence of a short circuit or break in the circuit. It helps in checking the output current of the circuit as well as the input and output voltage.
AC Test
The Ac test helps to detect and check the waveforms of the output signals of the circuit.
Functional Test
The function test measures the funtionality of the entire chip or specific blocks, this is a more comprehensive test and takes longer time.
Modern times have seen significant strides being made in terms of probe technology and we see it in the variety we now have when it comes to deciding what kind of probe card you wish to use to test your wafers. Let’s take a look at the different types of advanced probes:
Vertical Probe
Vertical probes are probe cards that are used to perform multi die testing of the likes of products associated with general logic and microcomputers. The needles are short and are positioned vertically when compared to the substrate, making it an ideal choice for small pad and high frequency wafers.
Photo: Probe Head Vertical (credit: Synergie-CAD)
MEMS-SP
This type of probe leverages the advantages of MEMS technology and allows you to use the probe card to test logic devices and microprocessors with high accuracy and reliability. MEMS stands for Micro Electro Mechanical System and is currently the most advanced form of probe technology available in the market. It can establish a connection to the wafer with one touchdown.
U-Probe
The U-Probe is a probe card that is best used for the measurement of memory devices. It only uses one contact or one touch down in order to establish a contact with a wafer that is up to 12 inches large. It also achieves an even scrub to yield the best possible results and can be used anywhere, in any position on the semiconductor wafer.
Probe cards are generally considered to be expendable and must be maintained in order to ensure their efficiency and performance. Due to overload as well as the accumulation of debris from the binding material of the wafer onto the needles or tips of the probe, the resistance may increase and impede proper measurement of readings. It is, thus, important to take care of the cleaning of the probe card and the needles.
Find here a list of IC testing companies.
Further reading: Introduction to LoadBoard Design and Production
Further reading: A Guide to Semiconductor Wafer Test
Further reading: Understanding Semiconductor Testing
Further reading: IC Testing Overview
