Advanced No-Clean Solder Paste for SIP applications

This paper reports the comparison of two solder pastes made using a no clean flux platform and ultrafine SAC305 powders of Type 7 and Type8+, made using Heraeus’ Welco® technology. The application tests were carried out using 008004 components, the smallest passives used in SiPs. For the paste with Type 7 powder, the application tests complete with 12hrs of stencil evaluation have been reported, whereas for the paste with Type8+ powder, a preliminary work-life evaluation has been reported. Both pastes have been compared for the release performance using area ratios down to 0.35, with both circular and square stencil opening apertures. Cleaning evaluation was carried out with some of the commercially available cleaning agents to assess the compatibility of the flux residue. It has been demonstrated that the no clean solder paste with Type 7 powder has excellent stencil work-life performance until 12hrs of printing, with voids after reflow being less than 10%. The paste with Type8+ shows better release performance vis-à-vis Type 7, down to area ratio of 0.35, for square stencil opening aperture. Results from cleaning evaluation show the leftover contamination can be fully removed.

Low-voiding solder pastes in LED assembly

Purpose This paper aims to investigate voiding phenomena in solder joints under thermal pads of light-emitting diodes (LEDs) assembled in mass production environment by reflow soldering by using seven low-voiding lead-free solder pastes. Design/methodology/approach The solder pastes investigated are of SAC305 type, Innolot type or they are especially formulated by the manufacturers on the base of (SnAgCu) alloys with addition of some alloying elements such as Bi, In, Sb and Ti to provide low-void contents. The SnPb solder paste – OM5100 – was used as a benchmark. The solder paste coverage of LED solder pads was chosen as a measure of void contents in solder joints because of common usage of this parameter in industry practice. Findings It was found that the highest coverage and, related to it, the least void contents are in solder joints formed with the pastes LMPA-Q and REL61, which are characterized by the coverage of mean value 93.13% [standard deviation (SD) = 2.72%] and 92.93% (SD = 2.77%), respectively. The void diameters reach the mean value equal to 0.061 mm (SD = 0.044 mm) for LMPA-Q and 0.074 mm (SD = 0.052 mm) for REL61. The results are presented in the form of histograms, plot boxes and X-ray images. Some selected solder joints were observed with 3D computer tomography. Originality/value The statistical analyses are carried out on the basis of 2D X-ray images with using Origin software. They enable to compare features of various solder pastes recommended by manufacturers as low voiding. The results might be useful for solder paste manufacturers or electronic manufacturing services.

Effect of flux functional group for solder paste formulation towards soldering quality of SAC305/CNT/Cu

Purpose The purpose of this paper is to investigate the wettability and intermetallic (IMC) layer formation of Sn-3.0Ag-0.5Cu (SAC305)/CNT/Cu solder joint according to the formulation of solder paste because of different types of fluxes. Design/methodology/approach Solder pastes were prepared by mixing SAC305 solder powder with different flux and different wt.% of carbon nanotube (CNT). Fourier transform infrared spectroscopy was used to identify functional groups from different fluxes of as-formulated solder paste. The solder pastes were then subjected to stencil printing and reflow process. Solderability was investigated via contact angle analysis and the thickness of cross-sectionally intermetallic layer. Findings It was found that different functional groups from different fluxes showed different physical behaviour, indicated by contact angle value and IMC layer thickness. “Aromatic contain” functional group lowering the contact angle while non-aromatic contain functional group lowering the thickness of IMC layer. The higher the CNT wt.%, the lower the contact angle and IMC layer thickness, regardless of different fluxes. Relationship between contact angle and IMC layer thickness is found to have distinguished region because of different fluxes. Thus it may be used as guidance in flux selection for solder paste formulation. Research limitations/implications However, detail composition of the fluxes was not further explored for the scope of this paper. Originality/value The quality of solder joint of SAC305/CNT/Cu system, as indicated by contact angle and the thickness of IMC layer formation, depends on existence of functional group of the fluxes.