Determine the Optimum Settings for Maximum Force (F_(max)) on Quad-Flat-Pack's (QFP's) using a Wetting Balance Machine

摘要

Solderability is an extremely important factor for electronics assembly. The majority of solder defects are attributable to poor (insufficient) component solderability. Testing for solderability is necessary. Within many electronics manufacturing companies a lot of focus is aimed at reducing the amount of soldering defects by carrying out sample solderability testing on batches of components using the Wetting Balance test method. Feedback from a variety of component suppliers indicate the main factors that influence the soldering characteristics for the Wetting Balance test are: Solder Temperature, Immersion Depth, Immersion Speed, and Dwell Time. Similar to the Dip and Look solderability test, there are various International Standards with varying settings for the aforementioned factors when trying to evaluate a components soldering ability using a Wetting Balance machine. A review of the International Standards such as J-STD-002C, IEC60068-2-54 and IEC68-2-69 was required to obtain the range of settings used for each of the factors. A matrix of all the settings within the standards was developed and from this a Design of Experiments (DOE) was set-up and conducted. It was decided to investigate the Wetting Balance test in more detail paying particular attention to Quad-Flat-Packs (QFP's). This paper focuses on the Fmax, maximum force reached during the Wetting Balance test. Fmax is one of a number of responses associated with the Wetting Balance test. Others include Tb (time to buoyancy), TFmax (time to reach Fmax), F1 (force after 2 seconds) and F2 (force after 5 seconds). The effect each of the four variables has on Fmax is determined by Main Effects and Interaction Plots. DOE 1 was set-up using Minitab and a total of 48 runs were carried out for the four factors. Each factor had two levels, high and low. A Pareto Chart of the Standardised effects showed all four factors had an affect on the Fmax. Immersion Speed had the largest effect - as the speed increases from 1mm/sec to 5mm/sec the Fmax increases. DOE 2 provided a more in-depth analysis of the four factors. Each factor had three levels, low, medium and high resulting in 81 runs. Again analysis was carried out using Minitab. The investigations and analysis from DOE 2 determined the optimum settings for a high Fmax using a Wetting Balance machine. These settings are Solder Temperature - 230°C, Immersion Speed - 0.5mm/sec, Immersion Depth - 0.5mm and Dwell Time - 4 seconds.