Metal Finishing EN Formulations Low Phos. Low Phos. n n Chosen for solderablity. n n Heavy metal stab. n n Difficult to control. n n No longer in use for PCB processing. Mid Phos. Mid Phos. n n Great general purpose plating. n n Not designed for PCB processing. n n Can skip plate. n n Still used for PCB processing.
9026M Electroless Nickel Specifically formulated for circuit boards n Consistent deposition rate over a wide range of bath loading. n No minimum work load! No Dummy panels! n Self pH regulating. n 1 to 1 replenishment. Easy to control. n No bail-out, far less to waste treat. n Works well with many types of soldermasks.
Electroless Ni Bath is Key to this Process Electroless Ni Bath is Key to this Process n Many problems seen in the industry come from the electroless nickel bath. n Two main process problems: Skip and Stray plating along with the main performance problem identified recently ; Black Pad. n Although other processes can influence these problems, most of the control is in the electroless nickel bath formulation and operation.
Electroless Nickel Bath Ingredients Electroless Nickel Bath Ingredients n NICKEL n REDUCING AGENT COMPLEXERS COMPLEXERS n ADDITIVES STABILIZERS STABILIZERS
EN Bath Additives Effect on PCBs EN Bath Additives Effect on PCBs n Key to Soldermask compatibility. n Controls phosphorus content and deposit characteristics/performance. n Determines operating temperature and plating rate. n Determines work load range. n Prevents bath decomposition from normal activator drag-in.
Type and Control of Additives are Critical n Control of replenishment is essential to proper electroless nickel operation as well as the properties of the deposit. n Over stabilized >> Skip (areas without EN)and black Pad (areas with EN). n Under stabilized >> Stray (EN creeps on to laminate or soldermask) n 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 n n Low type 1 additive and/or high type 2 Rough deposits Tank plate-out Background plating Black pad and possibly skip plate n n Low type 2 and/or high type 1 Edge pull back Low plating rate
Additive Levels n n When the additives are in balance, the deposit may appear normal. Higher than normal levels can cause problems that are not easy to detect. n n Assembly defects are usually detected too late. n n The goal is to eliminate the root cause of unseen defects rather than try to precisely control the levels.
Real World Processing- What Happens In Your Tank F Continued large replenishments can aggravate these higher than normal levels.
Cyanide Strip Test n n Indicates corrosion resistance of the nickel deposit. n n 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. n n 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 n Immersion Gold bath corrosion has been confused with as plated electroless nickel deposit structure. n Until now, little work has been done on the effects of the EN additives on both composition and structure.
Structure Vs 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? Whatever the cause, everyone will agree, assembly rejects are the major concern. n n What is the cause? n n How can a theory be proven? n n Analysis of failed parts is a requirement of any defect investigation. n n Once a mechanism is suspected, it must be tested by assembly.
Assembly Performance Testing Performed at independent test lab n n #1. Circuit patterns prone to black pad are selected for test. n n #2. Patterns are plated with two different EN formulas at four different stabilizer levels. n n #3. Wire leads are applied. n n #4. Leads are pull tested to failure.
Performance Testing Acceptability Criteria n n Pass Wire breaks, other than at neck Pad (foil copper) pulls from substrate n n Fail Wire separates from pad Neck of wire breaks
Assembly Performance Results- Pull Test
Solder Joint Shear Test Results
9026M Additives The EN System Improved ! n New Additives for improved circuit board performance (assembly). n Improved system eliminates break-down and co-deposition mechanism. No black pad.
9026M Deposit Shelf Life Testing Average Wetting 5 MTOs 85% RH + 85°F aging
Summary n Typical Metal Finishing formulations are not well suited for Printed Circuits. n Although some Additives are in low concentrations (ppm), they have profound effects on the deposit composition and structure. n When black pads are seen, higher than normal conventional Additive concentrations are usually the culprit. n Even at much higher than normal concentrations, the 9026M Additives will not cause assembly rejects.