omg fidelity electroless nickel immersion gold omg fidelity electroless nickel immersion gold...
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OMG FidelityOMG Fidelity
ELECTROLESS NICKELELECTROLESS NICKELIMMERSION GOLDIMMERSION GOLD
FIDELITY
Typical PCB ProcessTypical PCB Process
Acid CleanAcid Clean
MicroetchMicroetch
Palladium ActivatePalladium Activate
Electroless Nickel PlateElectroless Nickel Plate
Immersion Gold PlateImmersion Gold Plate
Metal Finishing Metal Finishing EN FormulationsEN Formulations
Low Phos.Low Phos.
Chosen for solderablity.
Heavy metal stab. Difficult to control. No longer in use
for PCB processing.
Mid Phos.Mid Phos.
Great general purpose plating.
Not designed for PCB processing.
Can skip plate. Still used for PCB
processing.
9026M Electroless Nickel9026M Electroless NickelSpecifically formulated for circuit boardsSpecifically formulated for circuit boards
Consistent deposition rate over a wide Consistent deposition rate over a wide range of bath loading.range of bath loading.
No minimum work load! No Dummy panels!No minimum work load! No Dummy panels! Self pH regulating. Self pH regulating. 1 to 1 replenishment. Easy to control.1 to 1 replenishment. Easy to control. No bail-out, far less to waste treat.No bail-out, far less to waste treat. Works well with many types of Works well with many types of
soldermasks.soldermasks.
Electroless Ni Bath is Electroless Ni Bath is KeyKey to this Process 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..
Electroless Nickel Bath Electroless Nickel Bath Ingredients Ingredients
NICKEL NICKEL
REDUCING AGENTREDUCING AGENT
COMPLEXERSCOMPLEXERS ADDITIVESADDITIVES
STABILIZERSSTABILIZERS
EN Bath Additives Effect EN Bath Additives Effect on PCB’son PCB’s
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.
Type and Control of Type and Control of Additives are Additives are CriticalCritical 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 BalanceEffect of Additive Balance
For many years, certain compoundsFor many years, certain compounds
(typically two or three types) are used(typically two or three types) are used
as additives in electroless nickelas additives in electroless nickel
formulations at PPM levels. They mustformulations at PPM levels. They must
be in balance to get an optimal nickelbe in balance to get an optimal nickel
deposit. Their balance or “ratio” has adeposit. Their balance or “ratio” has a
large effect on the depositlarge effect on the deposit
characteristics. characteristics.
““Out of Balance”Out of Balance”Deposit effects Deposit 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
Additive LevelsAdditive 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 Processing- Real World Processing- What HappensWhat Happens In Your TankIn Your Tank
NickelLevel
AdditiveLevel
AdditiveWith NiReplen.
AdditiveTotal
100% 100% 0% 100%90% 60% 40% 100%
80% 36% 80% *116%
70% 22% 120% *144%
60% 13% 160% *173%
Continued large replenishments can aggravate these higher than normal levels.
Cyanide Strip TestCyanide 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.
““Black Pad”?Black Pad”?Hard to tell by eye!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” =Hypercorrosion” =Much ConfusionMuch Confusion
Immersion Gold bath corrosion has Immersion Gold bath corrosion has been confused with as plated been confused with as plated electroless nickel deposit structure.electroless nickel deposit structure.
Until now, little work has been done Until now, little work has been done on the effects of the EN additives on on the effects of the EN additives on both composition and structure.both composition and structure.
Structure VsStructure Vs Composition Composition
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.
Test sample plated at both higher than
normal pH and temperature
What Is “Black Pad”?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.
Assembly Performance Assembly Performance TestingTesting
Performed at independent test labPerformed 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 TestingPerformance TestingAcceptability CriteriaAcceptability 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 Assembly Performance Results- Pull TestResults- Pull Test
0
20
40
60
80
100
50% 100% 150% 200% 250%
EN Bath Additive Concentration (% of Normal)
%Y
ield
aft
er T
est
Typically used additives 9026M Additive System
Solder Joint Solder Joint Shear Test ResultsShear Test Results
0
10
20
30
40
50
60
70
80
90
50% 100% 150% 200% 250%
Additive Level in EN Bath
% F
ail
afte
r 1
Kg
of
shea
rTypical Additive 9026M Additive
9026M Additives9026M AdditivesThe EN System Improved !The EN System Improved !
New Additives for improved circuit New Additives for improved circuit board performance (assembly).board performance (assembly).
Improved system eliminates Improved system eliminates break-down and co-deposition break-down and co-deposition mechanism. No “black pad”.mechanism. No “black pad”.
9026M Deposit9026M DepositShelf Life TestingShelf Life Testing
Average Wetting Forces @ 5 MTO’s
85% RH + 85°F aging
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0
0.6
1.2
1.8
2.5
3.1
3.7
4.3 5
5.6
6.2
6.8
7.5
8.1
8.7
9.3 10
time in seconds
mN
/mm
control
8 hrs
16 hrs
24 hrs
SummarySummary
Typical Metal Finishing formulations are not well Typical Metal Finishing formulations are not well suited for Printed Circuits.suited for Printed Circuits.
Although some Additives are in low Although some Additives are in low concentrations (ppm), they have profound concentrations (ppm), they have profound effects on the deposit composition and structure. effects on the deposit composition and structure.
When “black pads” are seen, higher than normal When “black pads” are seen, higher than normal conventional Additive concentrations are usually conventional Additive concentrations are usually the culprit. the culprit.
Even at much higher than normal Even at much higher than normal concentrations, the 9026M Additives will not concentrations, the 9026M Additives will not cause assembly rejects.cause assembly rejects.
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