8
FUJITSU Sci. Tech. J., 38,1,p.88-95(June 2002) 88 A Highly Reliable Halogen-Free Dielectric for Build-up Printed Circuit Boards vYasuhiro Yoneda vDaisuke Mizutani vNawalage F. Cooray (Manuscript received January 31, 2002) We have developed a highly reliable halogen-free (HF) flame-resistant epoxy dielectric for build-up printed circuit boards (PCBs). This material does not generate environ- mentally hazardous products such as polybrominated dibenzodioxins/furans or hor- mone disruptive agents like bisphenol-A and its derivatives. The dielectric is composed of a mixture of a reactive type oligomeric organic phosphate and Al(OH) 3 as the flame resistant. High Cu conductor corrosion resistance under high-temperature, high- humidity bias conditions has been obtained due to a cross-linkable organic phos- phate that reduces the free phosphate ion content. The newly developed dielectric has the thermal and mechanical properties required in mobile electronic devices such as hand phones and laptop PCs, for example, high flexibility and shock resistance. 1. Introduction Recently, due to the tremendous popularity of the Internet among the general public, demand for personal computers and mobile phones has been growing explosively. This will make millions of electronic devices obsolete within a couple of years, creating a massive environmental threat. To eliminate this threat, electronic device manu- factures have focused on developing environ- mentally friendly products such as Pb-free solders, halogen-free resins, recyclable Mg housings, and recyclable paints. In the printed circuit board industry, bromi- nated compounds are widely used as flame resistants; these brominated compounds are alleged to produce toxic substances, for example, polybrominated dibenzodioxins and dibenzo- furans, on combustion. The hazardous nature of the brominated compounds compelled us to search for new types of flame-resistant materials. As a result of our continuous efforts in this field, we have developed a new environmentally benign dielectric material composed of a non-toxic organic phosphate flame resistant. 1)-3) However, we felt that this material needed further improvements concerning the following points: The material causes conductor corrosion due to ion migration under high-temperature, high-humidity bias conditions, because of the relatively high moisture absorption of the or- ganic phosphate. Also, we have observed that the organic phosphate, which has a low mo- lecular weight, is slightly soluble in hot water. The organic phosphate is slightly soluble in aqueous alkaline solutions. As a result, the surface properties required for a satisfacto- ry peel strength (adhesion to Cu conductor) cannot be obtained. The base epoxy resin produces a notable amount of bisphenol-A and its derivatives at combustion; these compounds are suspected of being potent hormone disruptive agents. We have therefore made the following modifica- tions: To prevent the organic-phosphate from leach- ing out from the dielectric into hot water and

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Page 1: A Highly Reliable Halogen-Free Dielectric for Build … · mone disruptive agents like bisphenol-A and its derivatives. ... the unsaturated pressure cooker ... A Highly Reliable Halogen-Free

FUJITSU Sci. Tech. J., 38,1,p.88-95(June 2002)88

A Highly Reliable Halogen-Free Dielectricfor Build-up Printed Circuit Boards

vYasuhiro Yoneda vDaisuke Mizutani vNawalage F. Cooray(Manuscript received January 31, 2002)

We have developed a highly reliable halogen-free (HF) flame-resistant epoxy dielectricfor build-up printed circuit boards (PCBs). This material does not generate environ-mentally hazardous products such as polybrominated dibenzodioxins/furans or hor-mone disruptive agents like bisphenol-A and its derivatives. The dielectric is composedof a mixture of a reactive type oligomeric organic phosphate and Al(OH)3 as the flameresistant. High Cu conductor corrosion resistance under high-temperature, high-humidity bias conditions has been obtained due to a cross-linkable organic phos-phate that reduces the free phosphate ion content. The newly developed dielectric hasthe thermal and mechanical properties required in mobile electronic devices such ashand phones and laptop PCs, for example, high flexibility and shock resistance.

1. IntroductionRecently, due to the tremendous popularity

of the Internet among the general public, demandfor personal computers and mobile phones hasbeen growing explosively. This will make millionsof electronic devices obsolete within a couple ofyears, creating a massive environmental threat.To eliminate this threat, electronic device manu-factures have focused on developing environ-mentally friendly products such as Pb-free solders,halogen-free resins, recyclable Mg housings, andrecyclable paints.

In the printed circuit board industry, bromi-nated compounds are widely used as flameresistants; these brominated compounds arealleged to produce toxic substances, for example,polybrominated dibenzodioxins and dibenzo-furans, on combustion. The hazardous nature ofthe brominated compounds compelled us to searchfor new types of flame-resistant materials. As aresult of our continuous efforts in this field, wehave developed a new environmentally benigndielectric material composed of a non-toxic organic

phosphate flame resistant.1)-3) However, we feltthat this material needed further improvementsconcerning the following points:• The material causes conductor corrosion due

to ion migration under high-temperature,high-humidity bias conditions, because of therelatively high moisture absorption of the or-ganic phosphate. Also, we have observed thatthe organic phosphate, which has a low mo-lecular weight, is slightly soluble in hot water.

• The organic phosphate is slightly soluble inaqueous alkaline solutions. As a result, thesurface properties required for a satisfacto-ry peel strength (adhesion to Cu conductor)cannot be obtained.

• The base epoxy resin produces a notableamount of bisphenol-A and its derivatives atcombustion; these compounds are suspectedof being potent hormone disruptive agents.

We have therefore made the following modifica-tions:• To prevent the organic-phosphate from leach-

ing out from the dielectric into hot water and

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89FUJITSU Sci. Tech. J., 38,1,(June 2002)

Y. Yoneda et al.: A Highly Reliable Halogen-Free Dielectric for Build-up Printed Circuit Boards

alkaline aqueous solutions, we developed areactive type organic-phosphate.

• To improve the peel strength, a polyaromat-ic epoxy resin that is chemically stable inalkaline/KMnO4 etchant was used as themain component.

• To reduce the amount of bisphenol-Aderivatives generated at combustion, anon-bisphenol-A type resin was developed.Through these modifications, we were able

to develop a new halogen-free, bisphenol-A-freedielectric material that exhibits high corrosionresistance and strong adhesion to Cu conductors.

2. Experiments2.1 Dielectric preparation

The composition of the present dielectricformulation is shown in Table 1. An epoxy thatcontains a thermally and chemically stable naph-thalene ring was selected as the main resin. Inorder to obtain flexibility, a rubber modifiedepoxy resin was added as an elastomer. Also, byselecting a phenolic epoxy hardener having a flex-ible group, we achieved a 3-D network structurewith sufficient flexibility. The flame resistantsystem consists of a reactive type organic phos-

phate and Al(OH)3, which does not generate anytoxic gasses containing S or N.

The epoxy mixture was thoroughly dispersedin a bead mill and was coated to get 70 µm-thickfilms. The epoxy films were pre-baked at 120°Cfor 20 minutes and then cured at 170°C for 1 hourin an oven.

2.2 Combustion product analysisThe dielectric was burned at 400°C, 600°C,

and 700°C by using a CG-77 combustion gas sam-pler in a pure air atmosphere. The combustionproducts were absorbed in Tenax-GR (Poly(2,6-diphenyl-p-phenylene oxide + 30% carbon) at0°C. The absorbent was then placed in a gas sam-pler (JAS-100A) that was pre-heated to 230°C. Thevolatile components were then eluted bypurging and reabsorbed in glass wool at -60°C.The volatile components were then re-eluted fromthe glass wool by heat treatment. The eluate wasquantitatively analyzed by the GC/MS method.

Ultra-trace analysis of polychlorinated andbrominated dibenzodioxins/dibenzofurans in thecombustion products of the dielectric was carriedout at 600°C for 1 hour in an air atmosphere ac-cording to guidelines given by the Ministry ofHealth and Welfare of Japan.4)

2.3 Dielectric reliability evaluationTest specimens were prepared as follows. A

70 µm B-stage sheet of the dielectric was lami-nated and cured on a 50 × 50 mm core substratethat consisted of an epoxy/glass-fabric dielectricsandwiched between two Cu foils (18 µm). Onthe surface of the laminated film, a Cu conductorpattern was created (thickness = 12 µm, diame-ter = 6 mm). These specimens were subjected tothe unsaturated pressure cooker bias test(USPCBT) under the following conditions: T =121°C, RH = 85%, P = 1.7 atm, V = 20 V, t = 100 h.

The ionic impurities in the dielectric were es-timated as follows. The dielectric films were boiledin deionized water at 120°C for 48 hours in a closedTeflon bath, then qualitative and quantitative

Table 1Components of newly developed dielectric.

Component Chemistry

Rubber-modified epoxy

OH

Epoxy

Hardener

Accelerator Imidazole derivatives

Flame retardant

OH

OH

CH3 H3C

CH3 H3C

O OPReactive

part

Al(OH)3

2 2

O

O

R

n

n

P

O

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90 FUJITSU Sci. Tech. J., 38,1,(June 2002)

Y. Yoneda et al.: A Highly Reliable Halogen-Free Dielectric for Build-up Printed Circuit Boards

analyses of the water samples were done by ionchromatography.

2.4 Peel strengthThe surface of the cured dielectric was etched

in an aqueous alkaline KMnO4 solution, and thesurface morphology was inspected by microscopy.A 25 µm-thick Cu foil was deposited onto theetched dielectric surface by electroless-platingfollowed by electro-plating using Shipley platingsolutions. After drying at 120°C for 1 hour in anN2 atmosphere, the specimens were scored to pro-vide 10 mm-wide strips for peel testing. Testingwas done in a universal tester employing electronicload cells equipped with traversing fixtures toassure a 90° pull along the length of peel.

3. Results and discussion3.1 Combustion products

The GC patterns of the combustion productsof the newly developed dielectric (naphthalene

epoxy with reactive type organic phosphate) anda previously reported dielectric (bisphenol-Aepoxy with an additive type organic-phosphate)burned at 600°C are shown in Figures 1 (a) and(b), respectively.

From these figures, it can be seen there is adrastic reduction in the amount of bisphenol-Agenerated when the new material is burned. How-ever, a small amount of bisphenol-A was detectedeven in this sample. Because no bisphenol-Aderivatives were present in the new dielectric for-mulation, we believe that bisphenol-A is adecomposition product of the phenolic epoxy hard-ener.

Toxicological data of the p-containing com-bustion products of the additive type phosphateare shown in Table 2. The LD50 (Lethal Dose,50%) value of compound 2 is reported to be great-er than 15 800 mg/kg, suggesting that thiscompound is non-toxic. The LD50 value of theoriginal flame resistant is about 2000 mg/kg. This

CO

2C

O2

Ace

tone

Ace

tone

Ben

zene

Ben

zene

Tolu

ene

Retention time (min)

Abu

ndan

ce

Tolu

ene

Xyl

ene

Xyl

ene

Phe

nol

Phe

nol

Cre

sol

Cre

sol

Pro

pylp

heno

l

Pro

peny

ltolu

ene

Xyl

enol

Pro

peny

lphe

nol

Pro

pylp

heno

l

Pro

peny

lphe

nol

Ben

zofu

ran

grou

p

Phe

nol g

roup

Phe

nol g

roup

Ben

zofu

ran

grou

p

Ben

zofu

ran

grou

p

P c

ompo

und

2P

com

poun

d 3

Phe

nol g

roup

Ben

zofu

ran

grou

p

Ben

zofu

ran

grou

p

Bisphenol-A

(a)

(b) Bisphenol-A

0 4 8 12 16 20 24 28 32 36

Figure 1GC patterns of combustion products at 600°C.(a) Naphthalene type epoxy (reactive phosphate), (b) Bisphenol-A type epoxy (additive phosphate).

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91FUJITSU Sci. Tech. J., 38,1,(June 2002)

Y. Yoneda et al.: A Highly Reliable Halogen-Free Dielectric for Build-up Printed Circuit Boards

reveals that the use of this material is not aserious environmental threat. The LD50 value ofcompound 3 has not been reported yet.

3.2 Ultra-trace analysis of dioxins/dibenzofuransAlthough no chlorinated compounds were

used in the present formulation, it should be men-tioned that a trace amount of chlorine (ionic andcovalent form) was present at the impurity levelof 300 ppm in the epoxy resins. We believe thatthis impurity chlorine may generate dioxins anddibenzofurans. Therefore, we measured theamounts of dioxin and dibenzofuran that are gen-erated when the new dielectric is burned. Theresults are summarized in Table 3 togetherwith the dioxin levels generated by burning abisphenol-A type dielectric with different Cl con-tents.

Compound Oral LD-50(mg/kg)

>2000

>15 800

1750

(RO)2PO

(RO)3P = O

ROH

R: 2,6-dimethylphenyl

(RO)2PO OH

OP(OR)2

O

O

=

=

=

Combustion products

O

(1)

(2)

(3) -

2,3,7,8-T4CDDnote 2)

1,2,3,7,8-P5CDD

1,2,3,4,7,8-H6CDD

1,2,3,6,7,8-H6CDD

1,2,3,7,8,9-H6CDD

1,2,3,4,6,7,8-H7CDD

O8CDD

2,3,7,8-T4CDF note 3)

1,2,3,7,8-P5CDF

2,3,4,7,8-P5CDF

1,2,3,4,7,8-P6CDF

1,2,3,6,7,8-P6CDF

1,2,3,7,8,9-P6CDF

2,3,4,6,7,8-P6CDF

1,2,3,4,6,7,8-P7CDF

1,2,3,4,7,8,9-P7CDF

O8CDF

Total (PCDDs+PCDFs)

NDnote 4)

ND

ND

- note 5)

ND

0.0039

-

-

-

-

ND

ND

ND

-

0.0025

-

-

-

ND

ND

ND

ND

ND

ND

0.015

ND

-

ND

ND

ND

ND

ND

0.0025

ND

ND

-

ND

ND

ND

ND

ND

0.055 22

0.0579

0.0121

0.010 52

0.016 84

0.034 81

0.026 48

ND

0.071 01

0.074 51

0.0371

0.164 52

-

-

-

-

-

-

0.000 039

-

-

-

-

-

-

-

-

0.000 025

-

-

0.000 064

-

-

-

-

-

-

0.000 001 5

-

-

-

-

-

-

-

-

-

-

0.000 001 5

-

-

-

-

-

0.000 552

0.000 005 79

0.001 21

0.000 531

0.008 42

0.003 481

0.002 648

-

0.007 101

0.000 745 1

0.000 371

0.000 016 4

0.0251

Quantity (ng/g)

Dioxin compoundNaphtalene

type Bisphenol-A type

[Cl] = 360 ppm [Cl] = 100 ppm [Cl] = 900 ppm

TEQ note 1) (ng-TEQ/g)

Naphtalenetype Bisphenol-A type

[Cl] = 360 ppm [Cl] = 100 ppm [Cl] = 900 ppm

note 1) TEQ: Toxic equivalents (WHO-1998), note 2) CDD: Chlorinated dibenzodioxin, note 3) CDF: Chlorinated dibenzofuran, note 4) ND: not detected, note 5) -: below the detectable limit

Table 2LD-50 values (oral) of P- compounds (Additive type flameretardant and its combustion products).

Table 3Polychlorinated dibenzodioxin/furan combustion products of dielectrics.

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92 FUJITSU Sci. Tech. J., 38,1,(June 2002)

Y. Yoneda et al.: A Highly Reliable Halogen-Free Dielectric for Build-up Printed Circuit Boards

3.3 Unsaturated pressure cooker bias test(USPCBT)Figure 2 shows the interlayer resistance

variation during the USPCBT of the newly devel-oped dielectric ([Br] < 5 ppm, [Cl] = 880 ppm)together with that of a bromine-free bisphenol-A typedielectric ([Br] < 5 ppm, [Cl] = 130 ppm) and a con-ventional brominated dielectric ([Br] < 85 000 ppm,[Cl] = 230 ppm). Before the reliability test, all threesamples exhibited an interlayer resistance ofgreater than 1011 Ω. However, as can be seen fromthis figure, immediately after the test initiation, theresistance decreased significantly.

In the case of P-containing dielectrics(bromine-free), the interlayer resistance decreasedto the 107-Ω level and then remained unchanged,even after 100 hours. In the case of the brominat-ed dielectric, after about 5 hours, the resistancedecreased to the 106-Ω level. It is believed thatthe sudden decrease in the interlayer resistancemay be attributed to water absorption by the ma-terial. After the material reached the saturationlevel, the resistance remained constant. Howev-er, in the case of the brominated dielectric, it isbelieved that there is another reason for the lowerresistance compared with the other two dielectrics.

Figure 3 shows cross-sectional SEM photo-graphs of the dielectric/Cu interface after thecorrosion test. In Figure 3 (a) (brominated ep-oxy), some white particles can be seen at the Cu/dielectric interface; this phenomena cannot be

(a) (b) (c)

Migrated Cu

10 µm

Figure 3Cross-sectional images of the dielectric materials afterUSPCBT.(a) Br epoxy, (b) Bisphenol-A epoxy, (c) Naphthalene typeepoxy.

109

108

107

106

105

0 20 40 60 80 100

Naphtalene type epoxy (reactive phosphate)

Bisphenol-A epoxy

Br epoxy

Testing time (h)

Res

ista

nce

(Ω)

Figure 2USPCBT reliability test results (Test conditions: 120°C,85% RH, 1.7 atm, 20 V, 100 h).

From the present investigation it was foundthat the new formulation did not generate highlytoxic dioxins or dibenzofurans and generated sev-eral less-toxic substances in only very minutequantities; the total toxic equivalent was foundto be 0.064 pg/g. It should be noted that two com-pounds, H7CDD and P7CDF, are more easilygenerated compared with the other compounds,irrespective of the dielectric formulation.

Moreover, it was understood that thetoxicity level of the dielectric combustion productswould increase with the amount of Cl impuritythat is present. From careful analyses of the Climpurity level and the toxicity levels, we believethat a dielectric with a Cl impurity level of lessthan 1000 ppm would be environmentally safe.

In addition, we have investigated somebrominated dielectrics for bromodioxins andbromodibenzofuran liberation. In the case of acommercially available brominated dielectric withabout 10% bromine, a high concentration (1 ng/g)of bromodioxins and bromodibenzofurans wasdetected. Therefore, it is important to note thatif the toxicity levels of bromodioxins and bromod-ibenzofurans are clarified, we will be able todetermine the magnitude of the environmentalimpact of brominated chemicals.

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93FUJITSU Sci. Tech. J., 38,1,(June 2002)

Y. Yoneda et al.: A Highly Reliable Halogen-Free Dielectric for Build-up Printed Circuit Boards

seen in the other samples. These particles wereidentified as CuO by EPMA studies. Moreover,Br distribution at the interface was also moni-tored, and no unusual Br accumulation wasdetected.

The quality and quantity of ions extractedinto hot water from the dielectrics are summa-rized in Figure 4. It is important to mention thatthe Br- and PO4

3- ion contents in the watersamples were found to be extremely low; thissuggests that free Br- and PO4

3- ions were not themain causes for the weaker dielectric properties.

The striking feature of this data is the highconcentrations of organic acid ions such as ace-tate and formate that have been detected.Particularly, in brominated dielectrics, a high con-centration of formate (1400 ppm) was detected.We believe that these organic ions are mainlyresponsible for the lower dielectric resistance. Inother words, it can be said that to achieve a highdegree of corrosion resistance, the epoxy resinsmust be very pure.

Furthermore, it was understood that the useof reactive type organic phosphates instead of ad-ditive type phosphates prevents phosphate fromleaching out from the dielectric.

3.4 Adhesion to Cu conductorIn previous studies, we have found that bro-

minated dielectrics exhibit quite a strong adhesionto metals, while dielectrics with organic phos-phates exhibit comparatively poor adhesion.

It is well documented that in order toget a strong adhesion, micro-cavities should becreated on the dielectric surface so that the Cuconductor can enter them and becomeanchored to the dielectric surface. In the case ofbrominated dielectrics, we believe that Br com-pounds partially retard the etching process,creating an appropriate surface morphology withsufficiently large cavities as shown inFigure 5 (b). On the other hand, as shown inFigure 5 (a), bromine-free dielectrics with com-ponents that are soluble in KMnO4 solution areremoved from the surface during the etching pro-cess without creating cavities, leading to pooradhesion.

Previously, we have reported that the intro-duction of polyfunctional epoxies in bromine-freedielectrics significantly improves the adhesion tometals. From the present study, we have foundthat the introduction of epoxies containing a naph-thalene ring can further enhance the peelstrength.

The effects of the surface morphology andcavity depth on the peel strength are shown inFigures 6 and 7, respectively. The figures sug-gest that the peel strength increases with the

Con

cent

ratio

ns (

ppm

)

1500

1000

500

0

HCOOH-

CH3COOH-

HCOOH-

CH3COOH-

HCOOH-CH3COOH-

Cl- Cl-

PO43-

Cl-Br-

Br epoxy (PH 4.1)

Bisphenol-Aepoxy

(PH 3.9)

Naphthalene type epoxy (reactive phosphate)

(PH 4.4)

Figure 4Extracted ion concentrations (ppm) from dielectricmaterials.

Surface

Surface

Surface

Soluble

Insoluble

(a)

(b)

Figure 5Mechanism for surface morphology changes of dielec-trics in aqueous alkaline/KMnO4.(a) week peel strength, (b) strong peel strength.

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94 FUJITSU Sci. Tech. J., 38,1,(June 2002)

Y. Yoneda et al.: A Highly Reliable Halogen-Free Dielectric for Build-up Printed Circuit Boards

cavity depth. In order to get a peel strength ofabout 1.3 kgf/cm, the cavity depth should be about12.5 µm. However, the effect of cavity diameteron the peel strength remains unclear. Also, wefound that the introduction of polyaromatic ringsin the dielectric greatly reduces the susceptibilityto the etching process, while giving deep cavities

that result in a strong peel strength of about1.3 kgf/cm.

The physical properties of the newly devel-oped dielectric are summarized in Table 4,together with those of two commercially availabledielectrics. Among these dielectrics, the newformulation provides the best mechanical anddielectric properties. Specifically, it has the high-est tensile strength, elongation at break, adhesionto Cu, and decomposition onset temperature andthe lowest water uptake.

4. ConclusionWe have developed a new halogen-free

flame-resistant epoxy dielectric that has anon-bisphenol-A epoxy resin as the main compo-nent. The new dielectric has a high electricalreliability and peel strength and generates dras-tically less hormone disruptive substances duringcombustion than bisphenol-A type epoxies. Wefound that the toxic equivalent of the polychlori-nated dibenzodioxins/furans generated bycombustion of this material increases logarithmi-cally with the Cl concentration. We thereforepropose that the amount of chlorine content shouldbe less than 1000 ppm.

The use of a reactive organic-phosphate

Tensile strength (MPa)

Elongation at break (%)

Decomposition temp. (°C)

CTE α1 (ppm/°C)

α2 (ppm/°C)

Tg (°C, DMA)

Dielectric constant (1 MHz)

Dielectric loss (1 MHz)

Water absorption (%)

Flame-proof (UL94)

Peel strength (kgf/cm)

USPCBT

(120°C, 85% RH, 20 V, 100 h)

84

10

290

43

160

155

3.47

0.022

0.7

V-0

(Film)

1.3

OK

63

3.6

260

87

160

135

3.60

0.023

1.1

V-1

0.8

poor

67

3.5

260

76

192

135

3.60

0.03

1.3

V-0

1.2

NG

Halogen free

PropertyNew dielectric

Commercially available

dielectric

Halogen free Brominated

Table 4Properties of newly developed HF dielectric.

2.0

1.5

1.0

0.5

0.00.0 2.5 5.0 7.5 10.0 12.5 15.0

Surfaceroughness

Depth

Pee

l str

engt

h (k

gf/c

m)

Roughness or depth (µm)

: Naphthalene type epoxy dielectric: Copper laminated FR-4 (etched copper)

0 5 10

(a)

(b)

(c)

15 20 25 30 35

0

5

10

15

(µm)

(µm)

(µm)

05

1015

2025

Figure 6Effect of cavity depth on peel strength.

Figure 7AFM surface images of dielectric materials after etchingprocess.Peel strength: (a) 0.7 kgf/cm, (b) 1.0 kgf/cm, (c) 1.3 kgf/cm.

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95FUJITSU Sci. Tech. J., 38,1,(June 2002)

Y. Yoneda et al.: A Highly Reliable Halogen-Free Dielectric for Build-up Printed Circuit Boards

Yasuhiro Yoneda received the B.Sc.degree in Industrial Chemistry fromSeikei University, Tokyo, Japan in 1970.He joined Fujitsu Laboratories Ltd.,Kawasaki, Japan in 1970, where he hasbeen engaged in research and devel-opment of organic materials for micro-electronics. He is a member of theJapan Institute of Electronics Packag-ing.

Daisuke Mizutani received the B.Sc.degree in Chemical Engineering fromNagoya Institute of Technology, Nagoya,Japan in 1987. He joined Fujitsu Labo-ratories Ltd., Atsugi, Japan in 1987,where he has been engaged in researchand development of organic materialsfor microelectronics.

Nawalage F. Cooray received the B.Sc.degree in Chemistry and the M.Sc. de-gree in Organic Chemistry from the Uni-versity of Kelaniya, Sri Lanka in 1982and 1987, respectively. He received thePh.D. degree in Polymer Chemistryfrom Tokyo Institute of Technology, To-kyo, Japan in 1994. From 1983 to 1991,he was a researcher at the Ceylon In-stitute of Scientific & Industrial Research(CISIR), Colombo, Sri Lanka, workingon Organic Natural Products. From

1987 to 1988, he was with the National Chemical Laboratory forIndustry, Tsukuba, Japan, where he worked on NMR technologyfor organic materials. Since April 1998, he has been with FujitsuLaboratories Ltd., Atsugi, Japan. His current research interestsinclude high-performance dielectrics for PWBs, MCMs, and op-tical components.

prevents phosphate ions from leaching out fromthe dielectric into hot water and alkaline aqueoussolutions. It was found that the ion migrationmainly depends on the concentration of impurityorganic-acids in the dielectric. Therefore, thepurity of the resin components must be high toachieve a high-reliability dielectric. Strong adhe-sion to Cu has been obtained by using a chemicallystable naphthalene epoxy as the main component.It was observed that the peel strength was linear-ly dependent on the depth of surface cavities, andan average peel strength of 1.3 kgf/cm was obtainedwhen the cavity depth was 12.5 µm.

We are now developing recycling technolo-gies for this new material.

References1) Y. Yoneda et al.: A new halogen-free flame-

retardant dielectric with improved toughnessfor Build-up PWBs. Proc. of Electronics goesgreen 2000+, Berlin, 2000, p.133.

2) N. F. Cooray et al.: A New Halogen-FreeFlame-Resistant Dielectric for High DensityBuild-up PWBs. Proc. of 7th Symposium onMicrojoining and Assembly Technology inElectronics, Yokohama, 2001, p.211.

3) D. Mizutani et al.: The Dielectric Propertiesof New Halogen-Free Dielectric Material(FMS-HF). Proc. of EcoDesign2000 JapanSymposium, 2000, p.142.

4) The Ministry of Health and Welfare ofJapan: Notification No. 234 (December 1997),Guidelines for quantitative analysis of diox-in chemicals.