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LG enters chip packaging arena with Laser Direct Imaging machine, as TSMC's CoWoS remains constrained — maskless machine is designed to pattern fine interconnects, trading resolution for higher throughput
There could be another kid on the chipmaking tools block.
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As advanced packaging technologies like EMIB and CoWoS become yet another battlefield in the semiconductor industry, outsourced semiconductor assembly and test (OSAT) companies are trying new tools in a bid to offer services that others do not. This week, LG Electronics Production Technology Institute (PRI) signed a contract with an OSAT to supply it with a maskless laser direct imaging (LDI) lithography tool that can be used to build metal-interconnect patterns in semiconductor packaging, potentially with higher yields than currently available tools, reports ETNews.
LG-PRI's Laser Direct Imaging (LDI) system is a maskless lithography machine designed to pattern fine metal interconnects for advanced semiconductor packaging. While the company has developed various versions of the machine, its highest-resolution version can produce 1.5-µm line-and-space (L/S) patterns, which should be fine to 'print' wiring pitches of about 3 µm. The production equipment uses a 405-nm laser-diode light source and can process substrates as large as 600 × 600 mm, according to various media reports.
LG positions its LDI system primarily for advanced semiconductor packaging using organic and then glass substrates, displays, and MEMS. Yet, it can also be used to build high-density printed circuit boards (PCBs) for mobile devices or prototype purposes.
LG is entering an already established direct-imaging market led by KLA, Screen Holdings, Limata, and ORC, but participated in by a dozen manufacturers from Germany, France, Switzerland, Japan, and even China. What is notable is that LG is offering LDI systems with line/space capability down to 1.5-µm, which means it is targeting the higher end of the market. Yet, to establish a position, LG plans to price its LDI system competitively.
There are many ways to pattern substrates, including photolithography, e-beam lithography, nanoimprint lithography, and laser direct imaging, just to name a few. LDI is a maskless lithography process in which a laser exposes a digitally generated circuit pattern directly onto a photoresist-coated substrate, rather than transferring the pattern through a physical photomask. Instead of a photomask, an LDI system uses a digitally controlled pattern generator and projection optics, which resembles how a laser cinema projector projects a digital image onto a screen, except that LDI projects a circuit pattern onto photoresist. After development, the exposed resist leaves a pattern that defines where metal interconnects will be formed in later processing steps.
LG's LDI machine can produce down to 1.5-µm line-and-space patterns, which is good enough for chip substrates and even redistribution layers (TSMC CoWoS-R/-L uses RDL interposers with a minimum 4-µm pitch, or 2-µm line width/spacing). In contrast, competing products offer 1-µm, 3-µm, and 5-µm versions for different applications. While LDI in general cannot boast the resolutions offered by modern DUV, EUV, or e-beam lithography machines, LDI trades ultimate resolution for vastly higher throughput and large-area processing, exactly what the doctor ordered for production of PCBs or chip packaging. With current-generation LDI, the RDL interposer is the most advanced thing that these devices can pattern, as both CoWoS-S and CoWoS-L/EMIB-like technologies require considerably higher resolution. Meanwhile, there is another advantage that LDI machines have over lithography systems that rely on photomasks.
Because the image is generated digitally, the system can create and calibrate patterns in real time, while projection optics, precision alignment, and stage control position the pattern accurately on the substrate. This capability is important because the dimensions/geometry of packaging substrates can vary and because organic substrates can expand, contract, or w