A Focal Plane Array (FPA) is a sensor with a a two-dimensional detector pixel matrix, i.e. for infra-red light or X-rays, positioned in the focal plane of an optical system.
Typically, FPA can be found in thermal cameras, astronomical instruments, inspection systems, medical imaging devices, bolometers, weapon guidance systems and other kinds of measuring units used to visualize phenomenons in various spectral ranges of electromagnetic waves.
For the most part, sensors designed as FPA are rather large and - as opposed to other types of sensors - feature a number of small, independent detector zones. In order to work properly, a pixel-perfect connection to a readout unit (one or several read-out chips (ROCs) or ASICs) must be established. High pixel/bump counts and densities, tiny bump sizes and usually extremely small pitch make this a real challenge and have to be considered when choosing the best suitable bonding equipment and technology.
What are the Challenges?
- Pixel-perfect connection while dealing with extremely high bump counts and bump densities, tiny bump sizes and minimal pitch
- Particularly high demand for co-planarity and flatness
- High bonding forces proportional to bump count and bump size, avoid lateral drift
- Reduce required bonding forces by introducing controlled, uniform heat input methods
- High resolution optics with extended field of view: small bumps ≤ 5 µm but large sensor areas
- Working in cleanroom environments to avoid particle pollution
The Finetech Solution
In order to facilitate co-planar bump connection, a common method is to "coin" the bumps. Coining means that all bumps are slightly flatted and put to the same height level using special tooling.
Depending on bump material (Indium, gold, gold/tin, tin/silver/copper), pixel count, sensor size and other variables, the quest for the optimal bonding technology may return very different results.
Tack bonding is mostly used as an intermediate process stage, sometimes even as the final bonding process. During tack bonding, the bumps are pressed against each other with low temperature (bumps will not melt) and high force. If melting the bumps is required to establish a stable connection, a reflow process is appended after. If temperature and force are used to connect the materials in a diffusion process, this is called thermocompression bonding.
Also available are eutectic soldering methods with controlled heat input. Using them allows you to reduce bonding forces. Moreover, a dedicated use of process gas (i.e. formic acid vapor) is possible to employ various reduction processes. Essential when working with Indium bumps.
With a FINEPLACER® system you will always have maximum flexibility to choose the best suitable technology for your bonding challenge.
High Bonding Forces, Adapted Heating Plate and Tool Design
Integrated in the placement arm, the Bonding Force Module provides up to 1000 N.
Finetech offers reinforced heating plates which have been optimized for working with large bonding forces. With their 100% planar design, they help minimize the risk of laterally deviating forces (drift) during the bonding process which could compromise the bonding result. Due to the vacuum clamping, the substrate is always kept in place on the heating plate. Optionally available is a Process Gas Module for inert gas bonding.
Also part of the solution are pick & place tools which have been specifically adapted to detector carriers. In order to ensure co-planarity during touch-down and bonding, the tools come with integrated parallelism adjustment.
Vision System and Optics Shifting
For the visual alignment of such extremely small bumps (≤ 5 µm) you will need a high resolution alignment optics. A FINEPLACER® Vision Alignment System (VAS) helps visualizing super-fine structures. Various illumination options always provide you with optimal light settings, no matter the materials or surface conditions.
A particular challenge is the contradiction of tiny detector pixel on the one hand (demand for high resolution optics) and the large sensor area (demand for large field of view when aligning sensor and ROCs) on the other hand. With Finetech's Optics Shifting option, this contradiction is resolved in a stunningly simple yet very smart and efficient way.
FINEPLACER® Bonding Systems
Due to the modular design approach, FINEPLACER® bonding systems can be configured for virtually any application challenge.
The main distinguishing features between the machines are the
- degree of automation
- optical resolution and
- placement accuracy
Browse our product range or get in contact with your sales contact to figure out the best equipment solution for your specific application requirements.