ASM Assembly Systems
The advance in technology and its relentless development is delivering yet anothersurface mount assembly challenge. To meet the market demand for products with higher functionality whilst reducing the overall product size, the next generation of chip package isbeing readied upon the surface mount community. The Metric 0201 will have dimensions in the order of 0.25mm x 0.125mm, as a result the entire assembly process will be questioned as to its ability to deliver high volume/quality product.
This paper will look at the challenges of assembling the M0201 component in a high-volume manufacturing environment. The investigation will start with the printing process, with close attention to the impact of aperture and pad designs. The placement and reflow process will likewise be studied in detail.The resultant assemblies will be reviewed todeterminetheir suitability for a high-volume manufacturing environment. Discussion and conclusions will be directed at possible Metric 0201 assembly rules and the future challengers that exist.
From this investigation several findings have been gained. Industry guidelines and general rules of thumb claim that a finer particle paste will produce an enhanced print quality. However, it has been observed through this investigation that although a finer grain Type 6 solder paste material has produced a fuller print deposit for both pad designs, the resultant process capability has not followed this prediction. Both the printing and placement process have been negatively affected by the inclusion of excessive solder paste volume.
Within the printing process the excessive volume has caused the solder paste to saturate its designed area, thus causing the solder paste to merge into a neighbouringregion. Within the placement process an excessive volume of solder paste caused the pressure of the placement processto squeeze out the solder paste beneath the component’s termination. In the interspace examples of 50µm and 75µm this deformation of solder paste caused enough movement to form a solder paste bridge.
The Type 5 solder paste was not exempt from process issues andthe variation between deposits was still observed.However, the volume of solder paste was compatible with the application of Metric 0201 assembly.The main observation was a reduction of bridging errors on the finer interspaces.The inclusion of a conjoined track (P2 design) also added an additional challenge to the investigation. The track provides a path for the liquid elements of the printed solder paste andreflowed molten solder to migrate. The increased volume produced by the finer grain Type 6 solder paste material resulted in an increased propensity of bridging along the tracks from both the printing and reflow process. The additional issue with reflowed generated bridging is the tendency for the molten solder to alter the position of the components. This is due to the surface tension of molten solder overcoming the mass of the Metric 0201 component. The lower volume delivered by the Type 5 solder paste material produced lesssolder paste and reflowed bridging.
Within this investigation the assembly of Metric 0201 components have been accomplished with area ratios as low as 0.45, interspaces down to 50µm, a 60µm conjoined track and pad dimensions of 100µm x 115µm.The material selection for successful Metric 0201 assembly is as follows: 60µm fine grain stainless steel foil with a polymer coating and Type 5 grain sized solder paste.
Initially Published in the SMTA Proceedings