References cited in this section

1. Techni-Solder NF Acid process information sheet, Technic, Inc., Cranston, RI

2. Techni-Solder NF Acid material safety data sheet, Technic, Inc., Cranston, RI, 1991

3. Techni-Solder NF 80/20 Alloy High Speed Matte product data sheet, Technic, Inc., Cranston, RI

4. Techni-Solder NF 1957 product data sheet, Technic, Inc., Cranston, RI Fluoborate Plating Solutions for Tin-Lead

Any desired tin-lead alloy composition can be plated from a fluoborate solution. The composition of the deposit depends on the amount of stannous tin and lead in the solution, the type and amount of addition agent, the current density, and the tin-lead content of the anodes. Bath temperature and degree of agitation also affect the composition, especially in highspeed solutions.

Solution Components. Concentrated solutions of stannous and lead fluoborates and fluoboric acid are available commercially, so alloy plating solutions are made by mixing and diluting concentrates. Some compositions of concentrates are given in Table 3. The fluoborates of tin and lead contain free or excess fluoboric and boric acids for stability, and fluoboric acid contains free boric acid for the same reason.

Table 3 Composition of fluoborate alloy plating solution concentrates

Constituent

Amount

wt%

g/L

oz/gal

Lead fluoborate

Lead fluoborate, Pb(BF4)2

51.0

893

119

Lead, Pb(a)

27.7

485

65

Fluoboric acid, free HBF4

0.6

10.5

1.4

Boric acid, free H3BO3

1.0

18

2.4

Stannous (tin) fluoborate

Stannous fluoborate, Sn(BF4)2

51.0

816

109.0

Tin, Sn2(a)

20.7

331

44.3

Fluoboric acid, free HBF4

1.8

29

3.9

Boric acid, free H3BO3

1.0

16

2.1

Fluoboric acid

Fluoboric acid, HBF4

49

671

89.9

Boric acid, free H3BO3

0.6

8.3

1.1

Hydrofluoric acid, free HF

None

(a) Equivalent

The reason that excess boric and fluoboric acids provide stability in the fluoborate concentrates can best be shown by the reactions described below, with lead fluoborate used as an example, although the same is true for all other fluoborate concentrates. In the absence of boric acid, the metal fluoride will form. To stabilize the lead fluoborate, the following reaction takes place:

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