Transcript OMG Fidelity ELECTROLESS NICKEL IMMERSION GOLD

OMG Fidelity
ELECTROLESS NICKEL
IMMERSION GOLD
FIDELITY
Typical PCB Process
Acid Clean

Microetch

Palladium Activate

Electroless Nickel Plate

Immersion Gold Plate
Metal Finishing
EN Formulations
Low Phos.

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Chosen for
solderablity.
Heavy metal stab.
Difficult to control.
No longer in use
for PCB
processing.
Mid Phos.
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Great general
purpose plating.
Not designed for
PCB processing.
Can skip plate.
Still used for PCB
processing.
9026M Electroless Nickel
Specifically 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.

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
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ADDITIVES
STABILIZERS
EN Bath Additives Effect
on PCB’s

Key to Soldermask compatibility.
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Controls phosphorus content and
deposit characteristics/performance.
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Determines operating temperature
and plating rate.
Determines work load range.
 Prevents bath decomposition from
normal activator drag-in.

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 >> Skip (areas without
EN)and “black Pad” (areas with EN).
 Under stabilized >> 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.
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.
“Out of Balance”
Deposit effects

Low type 1 additive and/or high type 2
•
•
•
•
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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
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.

Real World ProcessingWhat Happens In Your Tank
Additive
Level
Additive
With Ni
Replen.
100%
90%
100%
60%
0%
40%
100%
100%
80%
36%
80%
*116%
70%
22%
120%
*144%
60%
13%
160%
*173%
Nickel
Level
Additive
Total
Continued large replenishments can
aggravate these higher than normal levels.
Cyanide Strip Test
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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.
“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.
“Hypercorrosion” =
Much Confusion

Immersion Gold bath corrosion has
been confused with as plated
electroless nickel deposit structure.
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Until now, little work has been done on
the effects of the EN additives on both
composition and structure.
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.
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.

Performance Testing
Acceptability Criteria

Pass
• Wire breaks, other than at neck
• Pad (foil copper) pulls from substrate

Fail
• Wire separates from pad
• Neck of wire breaks
Assembly Performance
Results- Pull Test
Typically used additives
9026M Additive System
%Yield after Test
100
80
60
40
20
0
50%
100%
150%
200%
250%
EN Bath Additive Concentration (% of Normal)
Solder Joint
Shear Test Results
% Fail after 1 Kg of shear
Typical Additive
9026M Additive
90
80
70
60
50
40
30
20
10
0
50%
100%
150%
200%
Additive Level in EN Bath
250%
9026M Additives
The EN System Improved !
 New Additives
for improved circuit
board performance (assembly).
 Improved
system eliminates
break-down and co-deposition
mechanism. No “black pad”.
9026M Deposit
Shelf Life Testing
Average Wetting Forces @ 5 MTO’s
85% RH + 85°F aging
0.3
0.25
0.2
0.15
8 hrs
16 hrs
0.05
24 hrs
-0.05
-0.1
-0.15
time in seconds
10
9.3
8.7
8.1
7.5
6.8
6.2
5.6
5
4.3
3.7
3.1
2.5
1.8
1.2
0.6
0
0
mN/mm
control
0.1
Summary
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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.