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Selective Plating for Surface-Mounted Component Lead

IP.com Disclosure Number: IPCOM000061747D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Elam, DL: AUTHOR [+4]

Abstract

A method is described which can eliminate the solder wicking problem, which is one of the biggest concerns in surface-mounted technology (SMT). One of the most frequently occurring solder defects in the SMT area is solder joints which open mainly because of the solder wicking to the component leads during solder paste reflow (see the figure). Some of the possible causes of solder wicking problems are as follows: -contamination and/or oxidation of pad surface, -solderability difference between component lead and pad (e.g., Sn or Sn/Pb vs. Cu), -differences of heat transfer due to different heat sink during reflow (pad vs. component lead or small sized component vs. big component), -coplanarity of component leads or misregistration of component, and -variability of component leads surface finishing.

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Selective Plating for Surface-Mounted Component Lead

A method is described which can eliminate the solder wicking problem, which is one of the biggest concerns in surface-mounted technology (SMT). One of the most frequently occurring solder defects in the SMT area is solder joints which open mainly because of the solder wicking to the component leads during solder paste reflow (see the figure). Some of the possible causes of solder wicking problems are as follows: -contamination and/or oxidation of pad surface, - solderability difference between component lead and pad (e.g., Sn or Sn/Pb vs. Cu), -differences of heat transfer due to different heat sink during reflow (pad vs. component lead or small sized component vs. big component), -coplanarity of component leads or misregistration of component, and -variability of component leads surface finishing. To prevent these wicking problems, this method provides a kind of semi-solder dam by adopting a different type of metallurgical surface finishing of SMC leads, as shown in the figure. Solderability of an Sn or Sn/Pb surface is, of course, much better than that of Ni or Cu/Fe finishing. Sn or Sn/Pb oxides can be easily removed by flux during reflow. However, this is not the case with Ni or Cu/Ni finishing. Most of the current SMC lead frame compositions are Cu or Cu/Fe, Fe/Ni/Mn. Also, most of component leads are coated with good solderable Sn or Sn/Pb with or without Ni plating onto the lead frame. Since most of the...