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PCB 表面处理-11-14-2006

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電路板焊墊表面處理 Final Finish for PCB

? Immersion Silver

? Immersion Tin
? Hot Air Solder Leveling ? Organic Solderability Preservatives

? Electroless Nickel Immersion Gold
? Acid Tin Plating

Industry Segments
Military Comp Indust

Biz/Instr Comm Auto

Finally Sn-3.0Ag-0.5Cu is the popular, and lots of experience already in the market in conjunction with OSP in Japan.
Composition Melting point (℃ ) 227℃ Advantage Disadvantage

Sn-0.7Cu

Good mechanical strength Good creep property Good mechanical strength Good creep property Lower melting point Good mechanical strength Lowest melting point Good wettability

High melting point Poor wettability High melting point Poor wettability Easily oxidized Bad wettability Weak mechanical strength Instable at high temp

Sn-3.0Ag-0.5Cu

221℃

Sn-8Zn-3Bi

197℃

Sn-58Bi

139℃

Sn-37Pb

183℃

Lots of experience

Weak creep property Thermal fatigue

Pull Strength Failure Mode
Crane Navel Surface Warfare Center
Failure at Board Surface

HASL OSP NiAu Silver Tin

0% 0% 21% 0% 2%

Source: US Navy

Solder or Laminate Separation
100% 100% 79% 100% 98%

Solder Joint Cracking due to Pb in Lead Free Joints

Elemental Mapping

Immersion Silver 浸鍍銀

賈凡尼效應
十八世紀義大利解剖學家賈凡尼,曾利用銅與鐵等 不同金屬鉤子鉤住生物體 ( 電解質 ),而發現電池性的電 流效應。為紀念其之發現後人在電化學方面常用其人名 “ Galvani “ 字尾加個c用以表達 “ 電池” 或 “ 電化 學 ” 之意念

安定
+0.799 +0.799

Tin -0.136 -0.136 Tin

活潑

Fe -0.44

Chemical Processing
Immersion Silver
CLEANER MICROETCH

Immersion Tin
CLEANER
MICROETCH PREDIP 1‘ 120F 1‘ 100F 1‘ 80F

Nickel Gold
CLEANER
MICROETCH 5‘ 120F 1‘ 100F

1‘ 120F 1‘ 100F 0.5‘ 80F 1‘ 120F

PREDIP
SILVER

CATALYST

4‘ 120~170F

6 Minutes

Tin

4~9‘ 150F

ACID NICKEL

1‘

80F

14 Minutes

15‘ 190F

GOLD

10‘ 190F

Micro voids on a single plane

Micro voids surface view

Good

Bad

Customer Z-Residues turn into voids

Immersion Tin 浸鍍錫

Formation of complex compound in the solution: [ Cu(TU)2]*MSA

Hot Air Solder Leveling 噴錫

浸SC銲料20.1秒

浸SC銲料22.41秒

浸SC銲料35.6秒

鎳如何影響錫-銅合金的性質
和“銅鎳”在IMC的結構有相似的六角形晶格

鎳取代銅?

晶格的直徑 幾乎相同 Cu6Sn5 Lattice Constants Melting Point a c 0.4125nm 0.5198nm 415 C Ni3Sn2 0.4190nm 0.5086nm 1246 C 1.6% difference 2.2% difference

Cu Erosion Comparison

OSP 有機保焊膜

Wetting Balance Characterization (3) Course of wetting force-time curve
State of the wetting of the sample
Wetting force (mN)

Time (sec)

(1)
Wetting force (mN)

(4)
Wetting force (mN)

Sample lead

Time (sec)

Time (sec)

(2)
Wetting force (mN)

Surface of molt ant solder

(5)
Wetting force (mN)

Time (sec)

Time (sec)

Electroless Nickel Immersion Gold 化學鎳金

1

2

3

4

引腳電鍍錫
Tin Plating




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