Electrolytic Copper
Plating Additives
and Contaminants
Wayne Jones
Electrolytic Copper Plating Chemistry
Typical DC Acid Copper Electroplating Solution contains:
Inorganic
• Sulfuric Acid (180 - 250 g/l)
• Copper Sulfate (40 - 100 g/l)
• Hydrochloric Acid (25 - 100 mg/l)
>
> Organic
• Brightener (2 - 10 mls/l)
• Leveler (5 - 15 mls/l)
• Carrier (25 - 100 mls/l)
> Water (Balance)
2
Electrolyte Control
Sulfuric Acid – Virtually unconsumed…Dragout
¾ Titration or Specific Gravity
Copper Sulfate – Maintained by Anode Erosion
¾ Titration, UV/Vis
Chloride – Maintained by chemical analysis
¾ Titration, Ion Specific Electrode, UV/Vis
3
Additives – Mostly Proprietary
Brighteners – are plating accelerators, which act as a micro-leveler and impact grain
refinement. They tend to be attracted to cathode induction zone points of higher electropotential, temporarily packing the area and forcing copper to deposit elsewhere. As the
copper deposit levels, the local point of high potential disappears and the brightener drifts
away, as well as depleting (hydrolysis) to a higher level of activity.
Chemical Family - Organic Sulfides, Disulfides, Thioethers, Thiocarbamates.
Levelers – are strong secondary plating inhibitors, which typically co-function with
Brighteners to reduce copper growth at protrusions and edges. They improve mass
transfer to localized sites of lesser electro-potential or feature height.
Chemical Family – Quaternary Nitrogen Cmpd.
Carriers – are plating inhibitors or suppressors, they create and maintain a defined
diffusion layer at the Anode (which regulate the flow of Cu+2 ions into the electrolyte and
ultimately to the cathode (board surface). Carrier depletion occurs as the PEG cleaves.
Chemical Family – Polyethylene Glycol (PEG), Polyalkylene Glycol (PAG)
Chlorides – mild plating inhibitors, which stabilizes the Cu+1 ion that serves as an
intermediate in the electro-deposition process during reduction to Cu +2. Additionally they
modify adsorption properties of carrier to influence thickness distribution.
Chemical Family – Hydrochloric Acid
4
Hull Cell – Additive Control
ASF 75, Needs Brightener
Carbon Treated Copper Bath
5
ASF 90, Proper Operating Range
CVS/CPVS – Cyclic (Pulse) Voltammetery Stripping
CVS/CPVS is an indirect bath
measurement which measures
the “combined” effect of the
additives and by-products
on the plating quality
6
CVS and CPVS Instrumentation
7
Copper Anodes
Phosphorized: 150 – 650 ppm P
Oxygen Free Casting
Grain structure grows from surface
to the center, resulting in uniform
corrosion of the anode.
Anodes are “conditioned” when new
by developing a necessary black
CuO film – Dummying.
Balls, Nuggets, Bars.
Typical Chemical Analysis
Contam inant
Concentration, Wt %
Lead
0.0002
Zinc
0.0001
Nickel
0.0002
Iron
0.0004
Sulfur
<0.0010
Antimony
0.0001
Arsenic
0.0002
Silver
<0.0010
Tin
0.0002
Anode surface area and continuous bath agitation is critical.
8
Pattern Plating
Full panel Electroless Copper deposition.
Photoresist apply, expose with positive image artwork majority of copper surface shielded, develop.
1)
2)
a)
b)
c)
d)
Plate Copper, Plate Tin (Etch Resist)
3)
a)
4)
5)
6)
7)
9
Reduced electroplated surface.
Lower current capacity required.
Less copper anode bank consumption.
Less copper in etchant.
Adds several additional wet process baths.
Strip Photoresist – Potassium Carbonate
Etch Copper – Ammoniacal
Strip Tin Resist – Nitric Acid
Antioxidant - BTA
Panel Plating
Full panel Electroless Copper deposition.
Full panel Electrolytic Copper plated.
1)
2)
a)
b)
c)
d)
Photoresist apply – Negative Image
Develop - Carbonate
Etch – Ammoniacal or Cupric Chloride
3)
4)
5)
a)
6)
7)
10
Higher current capacity required.
Significant copper anode bank erosion.
Smooth, even, bright finish on panel and hole walls.
Easily cleaned/prep’d for downstream processing.
Significant copper buildup in etch, more maintenance.
Strip – Potassium Hydroxide
Antioxidant - BTA
Contaminants – Drag in / Leach Out
Inorganics – ICP / GFAA analysis Trace Metals
¾ Iron (Fe)
¾ Calcium (Ca)
¾ Tin (Sn)
¾ Lead (Pb)
¾ Nickel (Ni)
¾ Antimony (Sb)
Organics – Hull Cell / CVS / TOC
¾ Cleaner/Predip surfactants (inactive)
¾ Resist Photo-initiators (inactive)
¾ Anode Bag Sizing (inactive)
¾ Additive breakdown products / fragmentation (active)
11
Chemistry Impact / FMEA
Defect / Failure Mode
Inorganic
CuS04
Burned Copper Deposit
Low
Poor Throwing Power
High
H2SO4
Cl-
Brightener
Low / High
Low
Low
Low / High
Leveler
Carrier
Low
Low
Poor Leveling
Roughness
Organic
Low
Pitting
Streaking
High
Poor response to additives
High
Step Plating
Grain Structure Poor
Low
High
Low
Anode Color Green
Low
High
Anode Color Dark
Low
Anode Color Bright
High
Soft Copper Deposit
Low
Brittle Copper Deposit
High
High
Low Tensile Strength
Dull/Matte finish
Copper Nodules
Spiked Copper Deposit
12
High
Low / High
Low
Contaminant & Process Impact / FMEA
Defect / Failure Mode
TOC
Particulates
Trace
Burned Copper Deposit
Poor Throwing Power
Poor Leveling
Mechanical / Electrical
Contaminant / Impurities
ASF
Anodes
Circulation
Agitation
Temp
High
High
High
Low
Low
High
High
Roughness
High
Low
High
High
Pitting
High
Streaking
High
High
Poor response to additives
High
High
High / Low
High
Filtration
Low
High / Low
High
Step Plating
Grain Structure Poor
Anode Color Green
Anode Color Dark
Anode Color Bright
Soft Copper Deposit
High
Brittle Copper Deposit
High
Low Tensile Strength
High
High
High
Dull/Matte finish
Copper Nodules
Spiked Copper Deposit
13
High
Low / High
Low / High
Burnt Plating – Unbalanced CD / ASF
14
Even After Microetch
15
Plating Characteristics Impact Etch Differential
16
Topography Differential – SEM/BSE
17
Copper Topography Variations (80x)
Burnt Copper Plating
Detectable
18
Transitional
Bright / Leveled
Spiked Copper – Surface / Knee
Courtesy Sanmina-SCI, Owego
19
Spiked Copper – Hole Wall
Courtesy Sanmina-SCI, Owego
20
Grain Structure Failure – Blind Via
Courtesy Sanmina-SCI, Owego
21
Copper Chicklets – Grain Structure
Courtesy Sanmina-SCI, Owego
22
Cobblestones – Hole Wall
Courtesy Sanmina-SCI, Owego
23
Cobblestones – Hole Wall
Courtesy Sanmina-SCI, Owego
24
Surface Nodule – Process Debris
Courtesy Sanmina-SCI, Owego
25
Surface Nodule - Debris
Courtesy Sanmina-SCI, Owego
26
Barrel Crack / Lam Voids – 6x TS
Courtesy Sanmina-SCI, Owego
27
Summary: Surface Contaminant Evaluation
Macro Level: PCB fabricator - SPC, IPC TM’s and spec’s, customer
requirements, cleanliness, water quality, post process residues,
solderability, visual inspection.
Micro Level: Post fab evaluations employing FTIR, Raman
Spectroscopy, HPLC, SEM - EDS/Auger, IC, ICP/GFAA.
What to look for:
¾Process residues (MOP, Resist Remnants, HW Salts, OSP)?
¾Co-plated contaminants (inorganic / organic)?
¾Hydrides, Oxides, Sulfides, Carbides, Halides?
¾Gas entrapment?
What’s changed the most:
¾Etch Resists (Sn vs Sn/Pb) and strip chemistry?
¾High Temp OSP’s?
¾DC or Pulse (Reverse and Duplex) Plating and chemistry – High aspect ratio?
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