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In this paper, a specially designed method for inspecting and categorizing whiskers in press-fit systems was established. Effect of PTH final hole diameter and pin coating thickness on whisker growth was evaluated. It was found that PTH final hole diameter showed more significant effect on whisker growth than pin coating thickness. The smaller the hole was, the more and longer whiskers grow in the press-fit system. However, thicker coating on pins introduced more scratched residue on annular rings and also could increase the chance of short circuit failure. The tin coating thickness on pins for telecom/datacom applications is recommended to between 0.5 μm and 2.5 μm.

Surface activation by palladium, either in colloidal or ionic form, has been widely accepted in printed circuit board industry. Palladium catalysts generally provide highly effective surface activation for electroless copper deposition on dielectric surface in making holes conductive (MHC) process. Unit price of palladium has almost doubled up in recent two years. The surge in unit price of this key metal in MHC process increases production cost of printed circuit board. The economic pressure leads to development of alternative catalytic chemistry which has lower cost and comparable, or even better, plating performance. Silver is another precious metal catalyst which shows promising experimental results in catalyzing electroless copper plating, and has the advantage of relatively stable metal unit price. However, new processes like silver catalyst need comprehensive data to demonstrate its industrial applicability without compromise the interconnect reliabilities.In this paper, the potential of silver catalyst process have been exploited and its corresponding performances in interconnect reliabilities were systematically studied. A standard test vehicle with and without preconditioning was used prior to the different kinds of thermal cycling tests. The test results were further supported by microstructural examination using advanced microscopy.

In this study, a series of factors that may affect whisker growth on electroplated tin coatings under high external pressure were studied by an indentation method, including storage time, coating thickness, loading and ball diameter. The indentation test results showed that longer storage time, thicker coating (< 3 μm), heavier loading and smaller inert ball could accelerate whisker growth. In addition, the insertion force, retention force and whisker behavior of compliant press-fit pins inserted into the same design of plated through holes with three different types of final finishes (Immersion tin, ENIG and OSP) were investigated.

Electroless plating of copper onto insulating substrates is a process broadly applied in the electronics industry for manufacture of printed circuit boards and decorative plating of plastic parts for automotive or consumer appliance. The key step involves surface activation of the dielectric surface for deposition in electroless copper bath. Palladium catalyst, either in its ionic form or metallic form, is most widely used for this purpose. However, the high and volatile unit metal price causes the catalyst solution to be the most expensive part among the electroless process. The economic pressure imposed on manufacturers and consumers would be the major driving force for developing an alternative catalyst system with lower cost. Previously we have introduced the innovative nano-silver catalyst system such as the physical properties, catalytic performance on conventional electroless copper deposition, and reliability performance in copper-copper interconnects area. [1] In this paper, comparison of silver catalyst with traditional palladium catalyst for MHC process will be described. Further study on deposition profile, microvia coverage and morphology, and reliability performance with liquid-to-liquid thermal shock will be illustrated. In the last section, the concerns on silver migration with silver catalyst applications on printed circuit board will be discussed.

This paper describes the development of a new ionic palladium catalyst, CIRCUPOSIT™6530 Catalyst, along with a tartrate-based horizontal electroless copper bath, CIRCUPOSIT™6550, to meet the performance demands of high-density-interconnect (HDI) and packaging (PKG) substrates in horizontal electroless copper plating. Implementation of the new ionic catalyst process is demonstrated through excellent coverage and reliability performance of through holes and microvias on HDI and PKG substrates following processing in horizontal equipment, as well as peel strength on low profile dielectric materials in the semi-additive process. Results also showed that the new CIRCUPOSIT™6530 Catalyst demonstrated stable performance during customer qualification.

One of the most challenging issues for printed circuit board (PCB) production is the metal plating at non-plated through holes (NPTH) during electroless nickel and immersion gold process (ENIG). It is believed that the undesired metal plating was induced by the excess palladium catalyst, which was adsorbed on the rough surface of the NPTH walls at the stage of make hole conductive process (MHC). The defect at the NPTH can lead to serious problems during product manufacturing. Redundant metal plating at the NPTH will alter the dimensional tolerance of the hole and affect the assembly of a device. If the device is unrecoverable, it will turn into very expensive scrap. Since ENIG is the final finishing step, it is crucial to eliminate metal plating at the NPTH to ensure the quality of the device before assembly. A general solution to metal plating at NPTH is pretreating the PCBs with thiourea and hydrochloric acid prior to ENIG process. However, thiourea is known to be carcinogenic and toxic to aquatic organisms. Additional time on extra process and costly waste treatment would be disfavored by many manufacturers. A palladium deactivation pretreatment process has been developed which can be integrated into the first two steps of ENIG process: acid cleaning and microetching steps. A NPTH Cleaner is developed for the deactivation of palladium residue at NPTH, replacing thiourea with non-carcinogenic and less toxic substances. Then a Modified Microetch will be applied for copper etching to ensure a bright metal finishing. The novel products are completely compatible with existing ENIG process where there is no additional operating time nor equipment installation required. The innovative pretreatment process can further expand the range of process window for ENIG, and result in higher efficiency.

Surface activation is an essential step in metallization of dielectric surface, which works together with the following electrolytic plating to build electrical connections between different layers of printed circuit boards (PCBs) or to build decorative and functional finishing layers of plastic substrates. Palladium, either in its ionic form or metallic form, is a traditional catalyst for many chemical reactions, including electroless metal deposition. However, due to its high and volatile unit metal price, major efforts are being focused on increasing its catalytic efficiency or identifying substitutes with lower cost. In this paper, we introduce a new catalyst system for conventional electroless copper deposition process — Nano-Silver catalyst. We studied physical properties of such catalyst including size distribution with transmission electron microscopy, zeta-potential with zeta-potential analyzer, localized surfaced plasmon resonance with UV-Vis absorption spectrometer. We compared its catalytic performance on conventional electroless copper deposition with traditional palladium/tin catalyst in terms of through hole copper coverage on resin and glass, thermal and mechanical reliability in copper-copper interconnects area, and also the stabilities of catalyst working baths and concentrate.

The implementation of Restriction of Hazardous Substances Directive (RoHS) in 2006 has led to a requirement that soldering materials used in the fabrication of printed circuit boards (PCBs) should be lead-free. This change has raised the peak reflow temperature by 30 C as compared with a tin-lead process. A protective surface finishing should be designed to maintain good solderability, by preventing the copper surface from being oxidized, both during storage after PCB fabrication and during exposures to soldering temperatures. Organic solderability preservative (OSP) is considered as a preferred low cost surface mount technology (SMT)-compatible non-metallic surface finishing method, due to the excellent surface co-planarity of the coated pads. However, the protectiveness of some commercial available OSPs is still poor and their solderability performances are always deteriorated after the multiple lead-free reflow cycles. This article presents experimental data to illustrate the newly developed OSP coating in terms of thermal resistance, copper diffusion suppression and solderability.