OMG Fidelity ELECTROLESS NICKEL IMMERSION GOLD

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OMG Fidelity ELECTROLESS NICKELIMMERSION GOLD
FIDELITY

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Typical PCB Process

• Acid Clean
• ?
• Microetch
• ?
• Palladium Activate
• ?
• Electroless Nickel Plate
• ?
• Immersion Gold Plate

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Metal Finishing EN Formulations

• Low Phos.
• Chosen for solderablity.
• Heavy metal stab.
• Difficult to control.
• No longer in use for PCB processing.

• Mid Phos.
• Great general purpose plating.
• Not designed for PCB processing.
• Can skip plate.
• Still used for PCB processing.

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9026M Electroless NickelSpecifically formulated
for circuit boards

• Consistent deposition rate over a wide range of
  bath loading.
• No minimum work load! No Dummy panels!
• Self pH regulating.
• 1 to 1 replenishment. Easy to control.
• No bail-out, far less to waste treat.
• Works well with many types of soldermasks.

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Electroless Ni Bath is Key to this Process

• Many problems seen in the industry come from the
  electroless nickel bath.
• Two main process problems Skip and Stray plating
  along with the main performance problem
  identified recently Black Pad
• Although other processes can influence these
  problems, most of the control is in the
  electroless nickel bath formulation and operation.

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Electroless Nickel Bath Ingredients

• NICKEL
• REDUCING AGENT
• COMPLEXERS
• ADDITIVES
• STABILIZERS

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EN Bath Additives Effect on PCBs

• Key to Soldermask compatibility.
• Controls phosphorus content and deposit
  characteristics/performance.
• Determines operating temperature and plating
  rate.
• Determines work load range.
• Prevents bath decomposition from normal activator
  drag-in.

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Type and Control of Additives are Critical

• Control of replenishment is essential to
• proper electroless nickel operation as well
  
• as the properties of the deposit.
• Over stabilized gtgt Skip (areas without
• EN)and black Pad (areas with EN).
• Under stabilized gtgt Stray (EN creeps on to
• laminate or soldermask)
• Consumption of Additives may not be
• equal to that of nickel and hypo. This will
  
• create an out of balance condition.

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Effect of Additive Balance

• For many years, certain compounds
• (typically two or three types) are used
• as additives in electroless nickel
• formulations at PPM levels. They must
• be in balance to get an optimal nickel
• deposit. Their balance or ratio has a
• large effect on the deposit
• characteristics.

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Out of BalanceDeposit effects

• Low type 1 additive and/or high type 2
• Rough deposits
• Tank plate-out
• Background plating
• Black pad and possibly skip plate
• Low type 2 and/or high type 1
• Edge pull back
• Low plating rate

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Additive Levels

• When the additives are in balance, the deposit
  may appear normal. Higher than normal levels can
  cause problems that are not easy to detect.
• Assembly defects are usually detected too late.
• The goal is to eliminate the root cause of unseen
  defects rather than try to precisely control the
  levels.

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Real World Processing- What Happens In Your Tank

• Continued large replenishments can aggravate
  these higher than normal levels.

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Cyanide Strip Test

• Indicates corrosion resistance of the nickel
  deposit.
• Does not show the difference between nickel oxide
  and bath by-products. Nickel oxide is normal and
  will not be a problem for assembly as long as the
  gold is present and of sufficient thickness.
• Strip time/temp and stripper bath composition
  have large effects on the appearance of the
  nickel.

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Black Pad?Hard to tell by eye!
A
H M Photos taken
after immersion gold was cyanide stripped.
This shows the boundary layer between the bulk
EN and the gold. H has a phosphorus content of
12. A and M both have a phosphorus content
of 7, with different stabilizers. High phos
nickel (H) has the highest corrosion resistance
to the stripping solution. Slight darkening from
nickel oxide (M) should not be confused with
unwanted bath compounds. Only A has detectable
amount of Additive byproducts.
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Hypercorrosion Much Confusion

• Immersion Gold bath corrosion has been confused
  with as plated electroless nickel deposit
  structure.
• Until now, little work has been done on the
  effects of the EN additives on both composition
  and structure.

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Structure Vs Composition
Test sample plated at both higher than normal pH
and temperature
This type of nickel structure has passed all
assembly criteria. Only extremely rough deposits
where nickel to nickel failure is likely will
cause assembly rejects.
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What Is Black Pad?

• Whatever the cause, everyone will agree,
• assembly rejects are the major concern.
• What is the cause?
• How can a theory be proven?
• Analysis of failed parts is a requirement of any
  defect investigation.
• Once a mechanism is suspected, it must be tested
  by assembly.

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Assembly Performance Testing

• Performed at independent test lab
• 1. Circuit patterns prone to black
• pad are selected for test.
• 2. Patterns are plated with two
• different EN formulas at four
• different stabilizer levels.
• 3. Wire leads are applied.
• 4. Leads are pull tested to failure.

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Performance TestingAcceptability Criteria

• Pass
• Wire breaks, other than at neck
• Pad (foil copper) pulls from substrate
• Fail
• Wire separates from pad
• Neck of wire breaks

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Assembly Performance Results- Pull Test
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Solder Joint Shear Test Results
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9026M AdditivesThe EN System Improved !

• New Additives for improved circuit board
  performance (assembly).
• Improved system eliminates break-down and
  co-deposition mechanism. No black pad.

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9026M DepositShelf Life Testing

• Average Wetting Forces _at_ 5 MTOs
• 85 RH 85F aging

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Summary

• Typical Metal Finishing formulations are not well
  suited for Printed Circuits.
• Although some Additives are in low concentrations
  (ppm), they have profound effects on the deposit
  composition and structure.
• When black pads are seen, higher than normal
  conventional Additive concentrations are usually
  the culprit.
• Even at much higher than normal concentrations,
  the 9026M Additives will not cause assembly
  rejects.