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Papers about slump

• Engineering Solder Paste Performance Via Controlled Stress Rheology Analysis

  by Dr. Anu Maria, K. P. Rangan, Rajkumar B. Raj, Dr. Ning-Cheng Lee, Dr. Xiaohua Bao

  Rheology of a solder paste has a significant effect on its stencil printing, tack, and slump performance. This paper describes a series of tests designed to investigate the rheological properties of a suite of solder pastes and fluxes, and the correlation with the solder paste performance prior to reflow. Data indicate that 1) print defect is proportional to the compliance (J1 and J2) and inversely proportional to the elastic properties (G’/G’’ and Recovery) and meta-rigidity (Yield Stress); 2) slump resistance is proportional to elastic properties (Recovery), solid characteristics (Stress [G’=G’’]), and rigidity ( êG* ê); 3) high elastic properties (Recovery), low compliance (J1 and J2), and low solid characteristics (Stress [G’=G’’]) are required in order to achieve high tack value. Good correlation between fluxes and solder pastes are observed for Yield Stress and Recovery only, suggesting those two properties are primarily dictated by fluxes.

  lead-free, pb-free, viscosity, flux, tack, slump, print, rheology, solder paste, soldering, solder

  [Permanent Link to this Paper]

  Posted on 1 Jan 2009

• Prospects of Solder Paste in Ultra Fine Pitch Era

  by Dr. Manchao Xiao, Kevin J. Lawless, Dr. Ning-Cheng Lee

  The 12 mil pitch processing is achievable with solder paste. It may also be the limit of solder paste printing technology, mainly due to the scooping problem associated with thin stencils. With decreasing pitch size, both smear and insufficiency rate increase. Tapering of stencil aperture helps thick stencil prints, but hurts on thin stencil printing. Aperture with orientation parallel to squeegee movement results in a higher print defect rate. Overall, use of fine powders is the most effective means to meet most challenges. It helps on achieving high performance in printability, tack, and non-slump, with acceptable trade-off in rheology and tack time. Solder balling may be the primary hurdle. The problem may be resolved by using inert reflow atmosphere or via flux chemistry improvements. A metal load of 90.5 to 91% seems to be the optimum for most properties.

  lead-free, pb-free, solder balling, slump, print, Fine Pitch, solder paste

  [Permanent Link to this Paper]

  Posted on 9 Mar 2010

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