Black pads

Immediately transfer the black pad to a Petri dish. Put about 3 or 4 mL of water in the Petri dish to cover the black cloth and then add 1 or 2 mL of alcohol. The alcohol is to keep molds fi-om growing so that you can keep the sample for a long period of time if you desire. 

The components are radically polymerized with 2,2 -azobis(2-methylbutyronitrUe) as initiator at 68-80°C. This base ink can be used for the formulation of a black pad printing ink. Eventually, such an ink can be used for a cosmetic pattern applied by inkjet printing on the contact lens (90). 

PTH Hole Fill Exposed Copper after Soldering Post-Assembly Corrosion of Exposed Surfaces Handling Defects Solder Bridging Plugged Holes Equipment Safety Paste misprints Black-Pad, Black-Line Nickel Brittle Fracture Solder Mask Attack RF Signal Loss Post-Assembly Corrosion of Exposed Surfaces Tin Whiskers Ionic cleaning Failures Solder Mask Attack Post-Assembly Corrosion of Exposed Surfaces Post-Assembly Corrosion of Exposed Surfaces Tarnish Solderjoint Microvoids Electrochemical Migration... 

Interfacial fracture is a failure mode usually associated with ENIG, and is also known as black-pad, brittle nickel, and black-line nickel (See Fig. 32.7). Technically, interfacial fracture simply refers to the location of physical separation when a solderjoint is tested to failure. Black-pad (black-line nickel) is a phenomenon of ENIG that, when sufficiently severe, results in interfadal fracture. Brittle nickel refers to the inherent weakness of solderjoints formed from nickel-tin intermetallics, regardless of the mechanism of failure. 

FIGURE 32.7 The result of black-pad and the microstructure of a black-pad nickel interface. 

Use function testing such as tape test and XRF to screen for black-pad. 

Package and PWB surface finish Black Pad, Brittle Failure, and Kirkendall voiding... 

When black pads are present, proper metallurgical bonding between the solder and the pad will not form during soldering. The occurrence of black pad is difficult to detect from the visual appearance of the PWB and solder joints. Boards with black pad can easily pass visual in-... 

This chapter reviews Uteratme on the microstructure of solder joints and the interactions of solders with substrates and related solder joint reliability issues. The substrates here are limited to Cu, Ni-coated Cu, electroless nickel/ immersion gold (ENIG), and hot air solder leveled (HASL) Sn-Pb. The solders are mainly Sn, eutectic or near eutectic Sn-Ag, and Sn-Ag-Cu alloys. Specific reliability issues discussed here include black pads of ENIG, gold embrittlement, compatibility of Pb-free solders with Pb-containing surface finish, and Kirkendall voids. 

Fig. 9 "Black pad" brittle interfacial failure in which the surface does not look black, (a) Pad/solder failure mode typical of failed BGAs on E-Ni/I-Au boards, (b) Low-magnification SEM photograph of fracture surface on PBCA solder ball side, (c) High-magnification SEM view of (b). (d) Low-magnification SEM photograph of the fracture surface on the pad side there is little or no trace of "mud" crack or corrosion trace, (e) High-magnification SEM view of (d). Source Ref 82...

FIG. 6 Planar separation characteristic of ENIG black pad problem. 

FIG. 7 Conditions that cause the black pad problem sometimes observed to occur with ENIG-t rpe finishes. (From Ref 4.)... 

Electroless Ni/immersion Au interconnects Investigation of black pad in wire bonds and solder joints, P. Snugovsky, P. Arrowsmith, and M. Romansky, J. Electron. Mater, 2001, 30, 1262. 

---