What is a semiconductor test board (ATE)?
ATE, the full name of which is Automated Test Equipment, is a device that performs automated functional and performance testing after wafers and chips are packaged. ATE equipment can perform chip parameter testing, functional testing, performance testing, fault detection, reliability testing, etc., and plays a vital role in the semiconductor manufacturing process.
As shown in the figure above, different types of ATE testers require different ATE boards.
Probe Card Board: Probe cards are used to test uncut and unpackaged semiconductor devices. By performing electrical tests on each chip on the wafer, devices with parameters within the required range are screened out for packaging.
Load Board: Load boards are required on Final Test test equipment. Load boards are used to perform functional or performance tests on devices after they are packaged, and to screen out defective devices after packaging. For ICs with high-speed interfaces, the corresponding load boards usually have strict impedance requirements.
Burn-in Board (BIB): Burn-in Board (BIB) is used for aging test of chip after packaging, such as thermal cycle or accelerated switching cycle, to expose the early failure of the device. The PCB material of the burn-in board must be able to withstand long-term and repeated exposure to high temperature environment and have extremely high reliability.
Requirements for PCB processing of ATE board
As integrated circuits (ICs) become smaller and more complex, the density and complexity of ATE test boards are also increasing.
Alignment accuracy and high aspect ratio
The number of layers of Load Board is usually more than 30, the BGA pitch is usually 0.35 to 0.5mm, the distance from drilling to conductor is less than 4mil, and the parallel test channels are: 4 sites, 8 sites, to 16 sites. Higher requirements are put forward for the inter-layer alignment, drilling accuracy, copper plating and resin plugging processes under high aspect ratio of PCB.
Ultra-high density test interface
The pitch of BGA on Probe Card is usually between 85~200um, and high-end products will be between 40~55um. Fine lines are close to the package substrate. If the lines exceed the PCB process capability, it is necessary to use the MLO/MLC adapter board of the package substrate process, and then test it after the adapter.
Flatness
The PCB of the probe card and high-end ATE has very high requirements for flatness, and the warpage should be controlled within 0.1%~0.2%. The pad height difference in the BGA area should be kept within 50um (2mil), and the range should be kept within 25~28um (1mil) when it is more stringent.
Appearance quality
Since the unit under test (DUT) area is connected to the pad through the probe, the pad must not be concave or damaged, and the gold surface of the pad must not have scratches or roughness problems.
Signal integrity
The high-end ATE board requires that the impedance tolerance is ±5%, and the stub length is less than 8 to 12mil. Due to the strict impedance requirements, the requirements for plating, etching uniformity and back drilling process capabilities are very strict.
