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Selective Etchant for Tin-Lead Composition Determination

IP.com Disclosure Number: IPCOM000061738D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Hurban, SS: AUTHOR [+5]

Abstract

Metallized ceramic substrate products typically utilize Cr, Cu, Cr metallurgy as the wiring plane 1 as seen in the drawing. A memory or logic chip 2 is electrically connected to the copper metallurgy plane 1 through solder pads 3 of 10/90 tin-lead. The substrate is connected to the card or board 4 through pins 5 with 63/37 solder 6. After pin insertion and swaging, the substrate is immersed into a molten 10/90 solder pot (not shown) where a solder coating is deposited over pins 5 to provide an electrical connection between pins 5 and Cu pads of the substrate and also deposits a tin-lead ball on the Cu fingers. These tin-lead balls provide electrical connection to the device circuitry through the chip-joining process.

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Selective Etchant for Tin-Lead Composition Determination

Metallized ceramic substrate products typically utilize Cr, Cu, Cr metallurgy as the wiring plane 1 as seen in the drawing. A memory or logic chip 2 is electrically connected to the copper metallurgy plane 1 through solder pads 3 of 10/90 tin- lead. The substrate is connected to the card or board 4 through pins 5 with 63/37 solder 6. After pin insertion and swaging, the substrate is immersed into a molten 10/90 solder pot (not shown) where a solder coating is deposited over pins 5 to provide an electrical connection between pins 5 and Cu pads of the substrate and also deposits a tin-lead ball on the Cu fingers. These tin-lead balls provide electrical connection to the device circuitry through the chip-joining process. The completed modules are joined to the cards through pins on the substrates soldered with a 63/37 tin-lead composition because the 63/37 composition melts to join the modules to the cards, but the 10/90 composition of the solder joints between the substrate and the devices is unaffected by the low heat. To ensure that the proper solder coverage is obtained is difficult because the 10/90 and the 63/37 are similar in appearance. An etchant formulation that selectively attacks the 10/90 solder to change its appearance makes the observation of solder coverage possible in the following manner. An etchant formulation of hydrogen peroxide and glacial acetic acid is used to preferentially etch pin/so...