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Development of preheat on solderability testing.

Zou, L; Hunt, C (2005) Development of preheat on solderability testing. NPL Report. DEPC-MPR 036

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As a means of evaluating the solderability of components and PCB pads in electronics assemblies, testing using a wetting balance has become widely established. However, existing solderability testing is carried out on components at ambient temperatures, a process which is not representative of typical surface mount processing, casting some doubts on the relevance of the test results. As part of a DTI-supported programme to further develop solderability testing, NPL has undertaken a study of the effects of preheating the components prior to the test immersion, in a way which more closely represents reflow soldering conditions.
This report describes the development of a suitable IR pre-heating system which can be used to heat test samples to controlled temperatures prior to test immersion, allowing testing at temperatures similar to those of reflow soldering. An optimum pre-heat temperature to achieve good solderability appears to be 55 ºC below the solder melting point. Higher preheat temperatures can provide misleading wetting data due to flux volatilisation.
Further, the results from an experimental matrix involving two solders (SnPb and SnAgCu), six solder test temperatures, superheats (temperature above the melting point) ranging from 5 to 50 ºC, and two fluxes, have been used to identify a set of suitable solderability test parameters. Using the preheating, good wetting can be achieved for SnPb with only 30 ºC superheat (i.e. an equivalent reflow temperature of 214ºC). In the case of SnAgCu alloy, a 10 ºC superheat (i.e. reflow temperature of 237ºC) is sufficient to achieve good solderability.

Item Type: Report/Guide (NPL Report)
NPL Report No.: DEPC-MPR 036
Keywords: lead-free
Subjects: Advanced Materials
Advanced Materials > Electronics Interconnection
Last Modified: 02 Feb 2018 13:16
URI: http://eprintspublications.npl.co.uk/id/eprint/3368

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