RU2351689C1 - Preferential etch of galvanic tin-and-leaden of coatings from copper basis - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to chemical metal treatment technology and can be used during the manufacturing of double-ended printed circuit board with blocking soldering mask for copper. Preferential etch of galvanic tin-and-leaden coatings from copper basis contains following components: fluoboric acid (40%-solution) 950.0 - 970.0 ml/l, hydrogen peroxide (35%-solution) 30.0 - 50.0 ml/l, copper nitrate (II) 0.03 - 0.04 g/l, potassium fluoride 5.0 - 8.0 g/l, sodium nitrate 5.5 - 7.5 g/l. While usage of proposed etchant etching rate of alloy tin-and-leaden more than ten times increases etching rate of copper basis.

EFFECT: decrease of destruction risk of metallisation in holes of printed circuit card and increasing of yield ratio at production of electronic products.

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Description

The invention relates to a technology for the chemical treatment of metals and can be used in the manufacture of double-sided printed circuit boards with a protective solder mask for copper.

Known solution for removing tin-lead coatings from a copper base, containing nitric acid, iron nitrate, sodium chloride and tin ion [RF Patent No. 22547424, IPC C23F 1/30, 2005].

This solution allows you to remove tin-lead coatings at a high speed, but it causes etching of the surface of copper, which increases the risk of destruction of metallization in the holes of the printed circuit board.

The closest to the proposed etchant in technical essence and the achieved result is a solution for etching galvanic coatings with tin-lead alloys containing hydrofluoric acid and hydrogen peroxide [USSR Author's Certificate No. 398702, IPC С23В 5/48, C23F 1/04, 1973 - prototype] .

The disadvantage of this solution is the relatively low selectivity of etching, as well as the formation of a film of sludge, which reduces the rate of removal of tin-lead coating.

The problem to which the invention is directed, is to increase the selectivity of etching of galvanic tin-lead coatings from a copper base.

This is achieved by the fact that a solution containing hydrofluoric acid and hydrogen peroxide additionally contains copper (II) nitrate and potassium fluoride as inhibitors of the copper dissolution process, and sodium nitrate when containing components as an additive that increases the etching rate of tin-lead:

hydrofluoric acid (40% solution), ml / l 950-970 hydrogen peroxide (35% solution), ml / l 30-50 copper (II) nitrate, g / l 0.03-0.04 potassium fluoride, g / l 5-8 sodium nitrate, g / l 5.5-7.5

This etch is a submersible type. It is necessary to pump the workpieces in the direction perpendicular to the plane of the printed circuit board. This leads to the fact that the solution is pumped through the holes of the printed circuit board, and therefore, the etching process of the tin-lead alloy in them is intensified. Removing the tin-lead coating is carried out by immersing the printed circuit boards in the bath with the etchant at a temperature of 18-30 ° C.

For experimental verification of the inventive etchant, three solutions of the proposed composition and one prototype solution were prepared. The contents of the components are presented in the table.

At a temperature of 20-25 ° C, a 40% solution of hydrofluoric acid is prepared. The required amount of a 35% solution of hydrogen peroxide and dry salts is added. Stir the solution until the salts are completely dissolved and let stand for one hour.

The etching rate of the tin-lead and copper alloy is determined as follows. On the PCM instrument, the metallization thickness is measured in the holes of the printed circuit board. Then, the boards are etched and every 30 seconds the MBS-10 microscope is monitored for the presence of tin-lead alloy in the holes. The time during which complete etching of the tin-lead alloy occurs is determined. The thickness of the remaining copper layer is measured on a PCM device. The thickness of the tin-lead alloy and its etching rate are calculated. Continue etching the board for five minutes and measure the thickness of the remaining copper layer. The etching rate of copper is calculated. The test results are shown in the table.

Table Etcher marking Component Content The etching rate, microns / min Hydrofluoric acid, ml / l Hydrogen peroxide, ml / l Copper nitrate, g / l Potassium fluoride, g / l Sodium nitrate, g / l Tin-Lead Alloy Copper Composition 1 950 fifty 0,03 6 7.5 4.0 0.35 Composition 2 970 thirty 0.04 7 5.5 3.0 0.20 Composition 3 960 40 0,035 7 6.5 3,5 0.25 Prototype 125 twenty - - - 3,5 1,5

The table shows that when using the proposed etchant, the etching rate of the tin-lead alloy is more than ten times higher than the etching rate of copper.

The use of the invention can significantly reduce the risk of destruction of metallization in the holes of the printed circuit boards, and therefore, increase the yield in the manufacture of electronic products.

Claims (1)

Selective etch of galvanic tin-lead coatings from a copper base containing hydrogen fluoride acid and hydrogen peroxide, characterized in that it additionally contains copper (II) nitrate and potassium fluoride as inhibitors of the copper dissolution process, and as an additive that increases the etching rate lead tin, sodium nitrate with components:
hydrogen fluoride acid (40% solution), ml / l 950.0-970.0 hydrogen peroxide (35% solution), ml / l 30.0-50.0 copper (II) nitrate, g / l 0.03-0.04 potassium fluoride, g / l 5.0-8.0 sodium nitrate, g / l 5.5-7.5