Presented at : The International Conference and Exhibition … · Disadvantages of Direct-Write ... •Automatic control of laser fluence down to ... Laser Direc Write, HDI, RCC,

Presented at: The International Conference and Exhibition on High Density Interconnect and Systems Packaging

Santa Clara, California, April 20th, 2001

Best of Session Award

Slide 1

M icroSound/ESI

HD International, Santa Clara, CA

A High-Density, Resin-Coated-Foil (RCF) Substrate Utilizing Mask and Direct-Write UV Laser

Photolithography

Scott Corbett*, Edward Swenson**, Jeff Strole*, Bill Beck*, John Yarno*, Thayer Hughes***

*MicroSound Systems, Inc.**ElectroScientific Industries, Inc.




Slide 2

M icroSound/ESI

Resin Coated Foil (RCF) buildup circuits provide solution for HDI

circuit boards:

• Laser-drillable dielectric

• Good planarity/thin metalization supports fine-line patterning.

• Compatible with existing board processes




Slide 3

M icroSound/ESI

FR4 Layer

RCF Layer 1

RCF Layer 2

Laser drilledvias

Typical RCF Buildup circuit:




Slide 4

M icroSound/ESI

HDI Buildup Circuit Issues:

•Trace/space smaller than 50µm/50µm requires expensive imaging and processing equipment

•Direct write imagers one answer to fine-line lithography but are there other solutions?




Slide 5

M icroSound/ESI

Advantages of Direct-Write

•Finer trace/space

•“Virtual” pattern can be scaled to match part geometry based on fiducial alignment

Disadvantages of Direct-Write

•Dedicated equipment and process materials required

•Slower throughput

•Potential raster image problems at small trace widths




Slide 6

M icroSound/ESI

Can Direct-Write be combined with Conventional Mask Imaging?

•Best of both worlds

– Use mask for large area exposure

– Use direct-write for fine detail exposure and precise alignment in select regions (ie. PGA layout region)

•However…..

– Direct-write process must be compatible with existing photomask resists and process methods




Slide 7

M icroSound/ESI

Is a UV laser-drill suitable for direct-write imaging?

•355 nm wavelength same as required for resist exposure (tripled-YAG)

•Vector control of beam position

•Automatic control of laser fluence down to 30mJ/cm2 (1-5 mW average power) in range required for resist exposure or ablation

•Serves dual purpose of drilling and patterning




Slide 8

M icroSound/ESI

Our process development tool:ESI 5200 UV laser drill

enables new interconnect architectures:

• Flexible pulse and power control

• Direct write ablation

• Non contact machining

• Non-rectilinear patterns

• Via drilling through die

• Direct-write photolithography

Tripled-YAG technology




Slide 9

M icroSound/ESI

Two potential approaches to UV laser direct-writing of photoresist:

•Resist exposure (low fluence level)

•Resist ablation (higher fluence, but still significantly lower than dielectric drilling)

Process compatible with:

– Positive or negative photoresist– Subtractive or additive process




Slide 10

M icroSound/ESI

Laser Exposure versus Ablation(Negative Resist Example)

Laser Exposure(Pattern traces)

Laser

Laser Ablation(Pattern spaces)

ResistMetalizationDielectric




Slide 11

M icroSound/ESI

Detail of Resist Ablation

Top of resist Bottom of resist12 µm 8 µm




Slide 12

M icroSound/ESI

Detail of Resist Ablation Showing Effect of Gaussian Beam:




Slide 13

M icroSound/ESI

Etched part:(10 micron trace/20 micron space)




Slide 14

M icroSound/ESI

Etched Line Pattern from Resist Exposure Process




Slide 15

M icroSound/ESI

SEM Detail of UV Laser Direct-Write Lithography Pattern

(using spin-on negative resist and laser exposure process)




Slide 16

M icroSound/ESI

5310 Optics Schematic

UV Laser

Collimator

BeamShaper

Imaging Galvos Scan Lens

Sample

ZBE




Slide 17

M icroSound/ESI

Via Via -- Top Diameter 18 µm Top Diameter 18 µm and Bottom Diameter 12 µm and Bottom Diameter 12 µm




Slide 18

M icroSound/ESI

Putting it all together to build an HDI substrate

•Fabricated two-layer, RCF buildup circuit on FR4 substrate (Polyclad CF400, C25T/B35T)

•Combined mask exposure and laser direct write lithography (exposure process)




Slide 19

M icroSound/ESI

PGA Redistribution Pattern (top layer)

1 1

White region-mask exposureRed region- laser exposure




Slide 20

M icroSound/ESI

Detail of Transition between Mask and Direct-Write Patterning




Slide 21

M icroSound/ESI

Completed Part:Detail of Laser Direct-Write Region




Slide 22

M icroSound/ESI

Combined Mask/Exposure Process Details:

• Laminate RCF Foil

• Laser drill vias

• Plate vias

• Apply resist film

• Pattern resist using mask exposure (mask opaque in laser direct-write regions)

• Further expose resist in fine-line regions using laser direct-write process

• Develop out resist

• Process using subtractive etching

• Strip resist




Slide 23

M icroSound/ESI

Summary

•Demonstrated use of UV laser drill as Direct-Write Imager

•Demonstrated both exposure and ablation of standard dry film resist

•Demonstrated combined mask/laser-write process (18µm trace in laser region)

•Application for high density HDI circuits for fine line patterning in array interconnect regions

www.microsnd.com www.esi.com

Documents

Presented at : The International Conference and Exhibition … · Disadvantages of Direct-Write ... •Automatic control of laser fluence down to ... Laser Direc Write, HDI, RCC,