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November 2004

AN2036

APPLICATION NOTE

Solderability Tests

Lead-free devices, from STMicroelectronics, are warranted to pass the solderability tests, and to form a

reliable solder joint with the base material of the circuit board, using Leaded (Sn-Pb) solder or Lead-free

(Sn-Ag-Cu) solder. This document describes the context of this assertion.

with the European directive on Restrictions on Hazardous Substances (RoHS) 2002/95/EU, and with the

IPC/JEDEC 020 standard for resistance to soldering heat and soldering process.

These devices have to be solderable with both Leaded materials and processes, and with Lead-free ma-

terials and processes. With a composition close to the ternary eutectic composition (Table 1.), the Tin-

Silver-Copper (Sn-Ag-Cu) alloy is considered as the standard lead-free material. Only Tin-Bismuth coated

devices are not tested in Tin-Lead solder. This is because the Tin-Bismuth coating is not recommended

for mixing with Tin-Lead solder, for board mounting, due to a reliability risk on the solder joints.

Table 1. Solder Composition for Solderability Tests

There are two kinds of tests that are applied to evaluate such ability of a surface to be wetted:

■

Dip and Look

■

Wetting Balance

Both tests are well known, and applied, worldwide. However, different methods are often used (such as

MIL standard 883-2003, JEDEC J-STD-002, JESD22-B102 and IEC 60749-21). The ones chosen by ST

are intended to cover the ones that are in most widespread use by our customers.

In these tests, the packages are “aged”, in order to test the solderability under the worst conditions and to

warrant at least 2 years of storage with no significant degradation of solderability.

Solder

Composition

Range (% weight)

Lead-free

Tin

94.6 to 96.6

Silver

3.0 to 4.3

Copper

0.4 to 1.1

SnPb

Tin

60 to 64

Lead

36 to 40