August, 2016
www.us-tech.com
Advances in Thick-Film Ceramic Technology Continued from previous page
Laser structuring also guarantees complete thick- ness at the line edges, however the laser struc- tured edges are not quite as clean as etched edges. This is because melting occurs during the laser handling and during the laser’s 850°C (1,562°F) firing process. The advantage of this method is that it is possible to structure inks that contain both gold and silver. Geometries are determined primarily by the
laser beam’s diameter. In our tests we used a laser beam diameter between 50 and 60 µm and struc- tured AgPt and AgPd inks. The best results were shown when using high-density gold ink.
Electroless Deposition Another way to finish the surface of thick-
film structures is to use electroless deposition. It is generally an adapted ENIG (electro- less nickel, immersion gold) process. The high conductivity of silver ink is combined with good solderability and provides a thick-film with resistance to leaching. This layer is compatible with all regularly used solders from SnPb to the lead-free family of SAC and AuSn. The surface also provides aluminum wire-bonds with high sta- bility for long-term, high-tempera- ture applications. For electroless plating, the
thick-film layer has to be optimized to protect it from the chemical processes. Otherwise the structures have to be covered by photoresist dur- ing the process. Currently, Cicor, is working on
an enhancement of the ENEPIG dep- osition process (electroless nickel, electroless palladium, immersion gold) to add the possibility of gold wire-bonding to the high performance of the NiAu system. The NiPdAu fin- ish will be a universal finish for many assembly processes.
MCM Interposer Interposers are needed for chip-
to-chip connection, or as carrier sub- strates between chips and electrical contacts to PCBs. Depending on the chip type for MCM (multi-chip module) or SIP (system in package), the sub- strates have to meet the requirements for wire-bonding or flip-chip bonding. Typical applications include:
l Digital circuits with processors
connections to the second level. l
and memory, which have several hundred first-level connections from chip to chip and nearly a hundred
nections to the second level. l
100 connections outside. l
Mixed-signal circuits, such as FPGA, with processors, memory, programmable logic, and analog parts with several hundred first- level connections from chip to chip and anywhere from 100 to 1,000 con-
for complex functionality with 10 to 50 chip-to-chip connections and 10 to
Analog circuits with different dies
applications, such as local distributed sensor systems, sensor nodes or wear- able medical devices, which have 50 to 100 chip-to-chip connections and 2 to 10 connections outside.
System in package for low power For the first two applications,
semiconductor manufacturing and equipment are required to build up the highly-complex substrates. A typ- ical interposer material is made of silicon TSV, or in the future, may be made of glass. These are very expen- sive if made in small numbers, but could be effective in the future. Cicor offers several options to
handle the last two applications, depending on special requirements. For RF-related applications or dense
See us at MD&M, Minneapolis, Booth 1114 Laser-structured gold fine-lines.
1 or 2 layer structures: thin-film or etched thick- film. For the highest wiring density multilayers: flex and rigid PCB substrates. Advanced thick-film, with its renewed set of design possibilities now covers the midrange
Page 49
between PCB and thin-film. This offers better mul- tilayer capability when compared with thin-film. When compared with PCB substrates, it offers much better long-term temperature stability and a better adaptation of CTE to the silicon or other chip materials. Thick-film technology is still improving after 50
years of use. Many applications require the longterm stability under harsh environmental conditions that thick-film can provide. The technology survived the RoHS and REACH legislations, which gave it its biggest boost in 20 years. With further new possibil- ities and materials, thick-film technology is poised to hold its position in microelectronics production. Contact: Cicor Americas, Inc., 185 Alewife
Brook Parkway, Suite 410, Cambridge, MA 02138 % 617-576-2005 E-mail:
info-americas@cicor.com Web:
www.cicor.com r
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