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Solder paste change



Solder paste change | 31 March, 2003

Hi, we are about to change solder paste for cost issue. Currently using a no clean Sn63 solder paste and tried several others, all no clean, Sn63 and Sn62. Want to ask about reliability test: we did thermal shock test for 8 days. The flux residue changed the color after the test: one whose residue was yellow became even darker, and transparent flux residues became white. Does this mean anything? In some products, we apply silicon coating.

Any other test we should go under before changing the paste? Thanks for your answers.

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Solder paste change | 31 March, 2003

First, most �thermal shock� recipes are not a reliability test. There is no relationship between the failures seem in these tests and in-use application. These tests show you the failures in these tests. That�s it!!!

Second, accelerated life tests, according to SM-785 - Guidelines For Accelerated Reliability Testing Of SM Solder Attachments, is a more realistic approach to solder connection life testing than thermal cycling.

Next, on a yellow flux residue that became darker during the thermal cycling: Yup, this can happen.

On transparent flux residues that became white during the thermal cycling: This was probably caused by water condensing on your board during the cycling.

On applying silicon coating over your low residue flux: If it works, it�s good. We see some coatings that work with some flux residues and some that don�t.

Any other test? * Compare the ionic contamination levels of your old flux and new flux. * Run surface insulation resistance tests on your new flux.

Continuing, J-STD-001, Appendix B talks to the qualification of new processes and process materials.

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Solder paste change | 7 April, 2003

Dear Yukim,

You may want to make sure that your presolder cleaning processes will support the change to a new flux. Many chemistries are vertically oriented and will clean only a selected few types of solder pastes.

If you find that a new cleaning chemistry is required, this could (and usually does) affect the waste stream management or even the type of machine used for cleaning stencils, misprints and tooling etc.

Good luck. Bill Schreiber Smart Sonic Corporation Tel: 1(800) 806-440R E-mail: Web:

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