SMT007 Magazine

SMT-Apr2015

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28 SMT Magazine • April 2015 no-clean. The first part of the study [1] focused on printing performance. The pastes were character- ized using standardized tests and internally de- veloped tests: dynamic viscosity, tackiness, slump and solderballing. The influence of accelerated storage at elevated temperature, the influence of time and conditions between printing and reflow and the influence of continuous shear according to time were shown. The printing performances were also evaluated in a printer. Although the number of pastes studied was restricted, the wa - ter-soluble pastes generally yielded results below the no-clean pastes with more sensitivity to tem- perature and humidity, tendency to slump dur- ing preheat and narrower printing window. Wa- ter-soluble solder pastes must be stored, handled and used with more caution before reflow. In the second part of the paper, the reflow properties will be compared: wettability, reflow rEliaBiliTy aSSESSMENT OF NO-ClEaN aND WaTEr-SOluBlE SOlDEr paSTES, parT ii continues FeAture process window, anti-graping properties. Final- ly the residue cleanability with water, then with water and detergents will be examined. The cleanliness will be assessed using visual inspec- tion, ionic contamination and surface insula- tion resistance tests. Experiments The pastes used for this evaluation were all made of SnAg3Cu0.5 (SAC305) alloy with type 3 (25/45 microns, -325/+500 mesh) particle size. The selected water-soluble pastes are named A, B and C and the no-clean pastes are named D, E and F. Metal content and flux designation ac- cording to J-STD-004A are given for each solder paste. A summary is done in the Table 1. The wetting properties of the pastes were assessed using on cleaned copper coupons, on copper finish FR-4 substrates, on test boards Table 1: Solder pastes characteristics. figure 1: Hotplate thermal profiles.

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