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SMT PCB板化学沉镍过程中磷元素对焊点的影响研究分析
  2024-02-05      50

文章来源:SMT工程师之家微信公众号

一、Why high Phosphorous? 為何需要高磷 ?

• E‘less Nickel with > 9.5% Phosphorous for minimized corrosion attack 

• Fear of “Black Pad” - ( 對 “ 黑鎳”的恐懼 ) 

• Improved solder joint integrity ( 改善焊接點的可靠性 )

  

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1、最高的耐腐蚀性

1)金浴浸泡侵蚀-无“黑垫”风险2)来自OSP工艺(SIT)的微蚀刻攻击-无镀金现象

2、改进了焊点的完整性

1)焊点的韧性断裂模式       -焊盘在焊料内拉出或断裂2)受控的Ni/Sn IMC生长       -薄而致密的IMC形成

二、磷含量的影響性(General influence of the Phosphorous content)

  

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1、磷层对镍层的影响(General influence of the Phosphorous content)

1)镍面的结构(Nickel Structure)

  

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三、高磷含量的沉鎳浸金系統(High P ENIG systems )

1、浸金制程中的攻击(Corrosion Resistance - Immersion Gold Attack)

  

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2、Corrosion Resistance - Micro Etch of OSP Process (SIT)

  

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3、抗硝酸腐蝕測試(Corrosion Resistance - HNO3 Acid Dip Test)

1)Why HNO3 test 为何需要硝酸測试? 

• quick test of quality of the e‘less Nickel layer 快速測验镍层品质; • “black and white“ result of sufficient P-content • process control tool on site

2)Test conditions 測試环境

• HNO3 50% V/V • at ambient temperature 室溫 • 30 sec 

3)Test sample layout 

• any layout plated with e‘less nickel (no gold - but can be used after Gold stripping) 

4)Pass / Fail criteria 

• no significant change in appearance 外观沒有明明改变

  

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四、General Process Development  (Soldering 焊錫)

1、Solder Spread Test 焊料扩展测试

  

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2、Solderability 可焊性功能 

1)Solder Spread 焊料扩展

  

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2)Multicore MUST II - Production data

  

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3、ENIG - Systems Solder Joint Reliability 焊点的可靠性

1)沉镍及浸金层厚度对BGAs位置发生断裂行为的影响(Influence of Plated ENIG Thickness to Fracture Behavior of BGAs )

  

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2)Ball Shear Test ( 球狀剪切試驗 ), usin

• Solder Mask Defined (SMD), Non Solder Mask Defined Pads (NSMD) 

• Lead containing solder balls

  

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3)BGA Fracture Behavior - Fracture Modes 断裂模式

  

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Fracture mode 断裂模式 : 

a. pad pull out (焊盘与基材分离)

b. between nickel and Sn / Ni IMC (在镍层与镍锡化合层之间) 

c. between Sn / Ni IMC and solder (在镍锡化合层与锡层之间) 

d. within the solder (在锡球內)

4)BGA Fracture Behavior - 600 µm SMD 结果

  

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5)ENIG Thickness for BGA 在BGA上所需的沉镍和浸金厚度

Highest number (> 80%) of “pad pull out“ seen at 600 µm NSMD pads 

a. with high Nickel (and high P) and low Gold thickness b. other fractures on these pads where within the solder joint

  

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6)BGA Fracture Behavior - Ball Shear Classification

  

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7)Influence of Ageing - Ball Shear Results 球狀

  

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8)Thermo Cycling (-55°C / +125°C)

  

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9)Ball Shear – Fracture 球狀剪切 - 断裂

  

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10)IMC Formation with Leadfree Solder 与无铅锡形成的镍锡化合层

  

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11)Phosphorous Enrichment at Nickel - IMC interphase

  

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12)Au-wire Bonding Bonding strength vs. Electrolytic Nickel Gold

  

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五、Conclusion 总結

1、Unique corrosion resistance 特殊的抗腐蝕效能 

2、Solderability as reliable as mid P ENIG 可焊性与一般中磷镍相约 

3、Superior solder joint integrity 焊点的可靠性高 

4、Excellent wire bondability (Gold and Al-wire) 优良的打线效能

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