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Ultra Thin Copper Foil with Carrier Foil
(Heat-Resistant Peelable Copper Foil) “F-HP”

1.

INTRODUCTION

Recently, mobile devices such as mobile phone etc. are
reducing in size and thickness, therefore printed circuitboard and semiconductor packages are required to besmaller and thinner. To meet this technological trend, ahigh density circuit wiring based on fine pitch patterning
is developed, and circuit wiring with width narrower than
30 μm are necessary. A thin and smooth copper foil isrequired to properly form such a fine pattern circuit.
The conventional subtractive process has a tendency toform trapezoidal cross section circuit geometry in fine pattern. Instead of this process, a fine patterning by semiadditive process is developed. In this process, copper isplated only on circuit wiring sections to increase copper
thickness. And copper foils between circuit wirings areremoved by dissolving. Therefore, a thin copper foil isnecessary to reduce volume to be dissolved.

2.

The main features of “F-HP”, which is our commercial
product, are shown in Table 1. “F-HP” has following features in comparison with our another peelable copper foilwith carrier “F-DP”.
1) A flat and smooth copper foil with thickness of 2 to5 μm, suitable for fine pitch patterns.
2) An ultrathin copper foil maintains the peeling performance at pressing temperature higher than 300°C.
3) A suitable surface treatment can be applied basedon customers requirements.

Structure of heat resistant peelable copper foil
CopperNodule

Ultrathin copper foil
2〜5 µ ｍReleaselayerCarrier foil
18 µ ｍFEATURES

Wiring L/S（Line & Space）（µ m）

Furukawa Electric has been selling F-WS foil as a fine
pitch pattern copper foil, however copper foil thinner than
9 μm has been a problem from the user’s handling pointof view. On the other hand, a copper foil thinner than
3 μm is necessary when wiring widths are narrower than
30 μm, as shown in Figure 1. To solve this problem, theultrathin copper foil with carrier foil, shown in Figure 2,
was developed. A release layer is formed on a support
foil (carrier foil) for handling on circuit forming. And, theultrathin copper foil with 2 to 5 μm of thickness is formedon the release layer.

7050Peelable
copper foil

（The ultrathin copper foilwith carrier foil）

20F-HP

10Figure 1

5Releaselayer
Heat pressing

Ultrathin copper foil

912Copper foil thickness（µ m）

18

Copper foil thickness required for fine pitch patternforming.

Peeloff

Carriercopper foil

Ultrathin copper foil

Resin substrate

Resin substrate①Heat pressing ofａ resin substrate ②Peel off a carrier
and a peelable foilcopper foil

Figure 2

F-HP configuration and usage.

Table 1Ultra thincopper foil

F-DP1 2 3

Carrier copper foil

F-WS
（Roughening foils）
Ｕ-WＺ（No roughening foils）

30

Peelable
ピー copper foil usage

Major features of F-HP.
Items

FeaturesThickness

2, 3 (,5) ( µm)

Release layer sidesurface roughness Rz

0.8~1.8 (µm)

Carrier foil

Thickness

18 ( µm)

Surface treatment

Roughening

Selectable

Carrier peelingstrength

Before heating≤ 0.02 (kN/m)

After press heated(180°C×90 min.)Peelable:≤ 0.03 (kN/m)

After press heated(300°C×10 min.)Peelable:≤ 0.03 (kN/m)

Furukawa Review, No. 38

20101Ultrathin Copper Foil with Carrier Foil (Heat-Resistant Peelable Copper Foil) “F-HP”

3.

CHARACTERISTICS

3.1 Flatness and Smoothness
The surface profile of the ultrathin copper foil, after thecarrier foil peeling off, is shown in Figure 3. A carrier foilside surface of the ultrathin copper foil is very flat andsmooth. Then both linearity at wiring tip and rectangularity
at wiring cross section are kept in good shape, after wiring finer than 30 μm. Therefore, the ultrathin copper foil issuitable for fine pitch patterning.

Measuringpoint

100 µ m2 µm

Figure 5→−5.00

Surface roughness measuring point（µ m）

2 µm

Roughening (big)Examples of Surface treatment results by various
copper nodules.

100Surface roughness measurement result by laser microscope（Distance from the average surface position）

Measurement result for surface profile of ultra thincopper foil.

3.2 Heat ResistanceThe carrier peel strength is measured after pressing for one
hour with a range of temperatures Figure 4. F-DP isdesigned to be applied on epoxy resin substrate material.
Therefore, the lamination on resin base material, withpressing temperature higher than 200°C, induces high carrier peeling strength as shown in Figure 4. And, some difficulty is experienced when peeling off the ultrathin foil fromcarrier foil.
Recently, more often, the heat resistant resin with highglass-transition temperature ( Tg) is applied on a circuit
base with reduced-size high density wiring package. F-HP
is applicable to the high Tg resin, and maintains the stable peeling strength for heat resistant resin with press
temperature higher than 300°C.
Carrier peeling strength（kN/m）

2 µm

No roughening+5.0
Average

Surface roughness（ µ ｍ）

Peeled surface

Figure 3

3.3 Surface Treatment
A surface treatment, applied on the surface to be pressed
onto resin substrate, can be selected from several kindsof treatments, depending on a given application. For
instance, big coarsened particle surface treatment forhigher adhesion with resin, low coarsened or non coarsened surface treatment to form extremely small wiring, areavailable.
The examples of surface roughening treatment on theresin pressing side of the ultrathin copper foil, with several
sizes of copper nodules, are shown in Figure 5.

4.

IN CONCLUSION

The ultrathin copper foil with carrier foil (the heat resistantpeelable copper foil) F-HP is a flat and smooth ultrathin
copper foil which is suitable for fine pitch forming. This isfabricated using the additive method and has an excellent
performance for application on heat resistant resin which
requires pressing temperature higher than 300°C.

For more information, please contact:
Sales Department, Copper Foil Division, Metals Company
TEL: +81-288-22-3490
FAX: +81-288-22-3479

0.10.09

F-DP
F-HP

0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01

0150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330

Temperature（℃）

Figure 4

Relation between pressing temperature and carrier
peeling strength.

Furukawa Review, No. 3820102