Unique TwinRevolve placement technique brings high-volume assembly to flip chips

By: Boudewijn van Blokland, Associate Director, Product Manager Die Bond 

Flip chips are often more suitable by design than wire-bonded chips for high-performance electronic circuits. Short, thick copper pillars replace long, thin and relatively fragile wire bonds. That gives a step-change improvement in high-frequency performance, power dissipation, heat transfer, ratio of die-to-package area, and reliability. 

Despite the benefits for low pin-count packages, flip chips have seen only limited use because flip-chip device assembly has been difficult and relatively expensive. Current Flip Chip assembly flow is to pick from wafer, flip, flux, dip and then place. That demands delicate and precise handling, so device assembly has in practice been limited to a slow 12,000 devices/hour. For smaller dies, speed is even slower because dipping the die in flux and pulling it out can only be done at a relatively slow speed. High volume manufacturers requiring over a million devices a day would need multiple machines working full time, which would need a massive investment. 

At 60,000 devices/hour and 24/7 operation, ITEC’s ADAT3 XF TwinRevolve flip-chip die bonder can assemble over eight million devices a week. That replaces five conventional machines, making it a game changer for flip-chip assembly. It needs only a fifth of the factory floor space, with corresponding savings on maintenance, operator hours, spare parts, tool shipment and energy costs. Which means a much smaller carbon footprint, and a fraction of the Total Cost of Ownership (TCOO). 

Rather than using the stop-start motion of conventional linear placement heads, our design uses twin synchronized rotating heads (“TwinRevolve”). Each cycle picks, flips and places chips at >16 chips a second with a controlled smooth motion to reach the 60,000/hour. The circular motion means less inertia and vibration, allowing a similar accuracy (better than 12 μm @ 3σ) as previous machines but at much higher speeds. 

Assembling devices with up to around 100 pins, the machines allow IDMs (Integrated Device Manufacturers) and OSATs (Outsourced Semiconductor Assembly and Test) to extend their flip- chip capacity and even upgrade their high-volume wire-bonded products to a new generation. 

In flip chips, the relatively thick copper pillars have a fraction of the connection resistance, parasitic capacitance and parasitic inductance of wire bonds. That improves electrical performance by reducing signal degradation and ElectroMagnetic Interference (EMI). This in turn means higher circuit speeds. 

The virtually negligible thermal resistance of copper pillars eliminates the (small) heat loss associated with wire bonds, with better heat transfer allowing higher power dissipations: essential for high-power applications. And it eliminates wire-bond failures like broken/sagged wire, wire sweep and lifted bonds to improve reliability. 

Eliminating the wires also increases the available package space because the length of wire from die to lead/wedge position is not needed. The higher interconnect density thus allows more silicon/functions in the same package size.

Figure: The first rotating head picks and places non-flip chips, and hands over flip chips for placement by the second rotating head.

There’s full servo-controlled bond-force/pick-force, and auto diagnostics check the machine’s health status. A separate flux screen printer can be added as an inline-setup connected to a screen printer at the input side or reflow oven at the output side. Alternatively, the TwinRevolve can run as a standalone tool with strip magazine input/output. 

Optional flux-related inspection includes droplet size and shape and coverage with respect to copper pillar size. This option is implemented on the inspection shuttle before the strip is transferred to the attach shuttle, where the actual flipped die is placed in the flux with a very low bond force. The XF TwinRevolve handles strip information via the E-142 strip ID protocol to guarantee full die and flux traceability. 

Five high-resolution (up to 5 Mpixel) cameras at key process points on the TwinRevolve help to keep operation under close control. They monitor the flux size, pre-pick, bump size, chipping on the top side, and rotation and chipping for the back side. All these can be monitored without speed loss. XYR   and chipping can be detected in the post-bond image. Sidewall inspection can also be installed as an option. 

The die bonder takes several types of leadframes like QFN, DFN, HVQFN, SOT, SO, TSSOP and LGA. So, both leadless and leaded packages are covered, also giving the option to bond directly chip on lead. The machine can handle 100x300 mm strip size. 

Automated operation is on the roadmap to allow the machines to work in the ‘factory of the future“. They will be particularly suitable in view of their compactness and the number of flip-chip assemblers they replace. 

The machine accepts 8- to 12-inch (200- to 300-mm) wafers. Further options allow connection to AGV AMR or OHT autoloaders for strip magazines (in-outgoing) for handling magazines, and are optionally enabled with E142 substrate mapping. There’s an automatic wafer change with barcode reader and full die traceability, auto recipe download and SECS/GEM interface. 

Like other die bonders and die sorters in ITEC’s ADAT3 XF (eXtended Flexibility) range, the new flip-chip die bonder is modular and field upgradable for extended lifetime and more sustainable operation. With more than 100 billion pick and place actions annually, ITEC is a supplier of choice for high volume manufacturing.

Contact us to learn more about the ITEC ADAT3 XF TwinRevolve: salesmarketing@itecequipment.com. 
 

About ITEC

Headquartered in Nijmegen, the Netherlands, ITEC is a back-end semiconductor equipment manufacturer specializing in high-volume production of semiconductors. ITEC provides the highest productivity assembly, test, inspection and Smart manufacturing platforms, targeting mass volume manufacturing from small signal to power MOS devices. 

ITEC is rooted in semiconductor manufacturing, combining over 30 years of state-of-the-art equipment and automation expertise as partner to Philips and Nexperia. In 2021, ITEC became a separate legal entity. For more information, visit our website at www.itecequipment.com. 

Press contact:
Ksenia Tantsurina
Marketing Communication Manager
Email: salesmarketing@itecequipment.com