Almit’s LFM 48 N dipping paste is a powerful alternative to gel pastes traditionally used in BGA PoP (Package-on-Package) stacked device applications and is ideal for holding larger area devices that often exhibit warpage during reflow. The new paste is a combination of ultra-fine solder spheres and a flux vehicle optimised for a long open time in a dipping tray. It offers reliability advantages to board assemblers at both solder melt and peak reflow temperatures. LFM 48 N is expressly designed to deliver consistent dipping transfer characteristics coupled with a strong tack performance to hold large devices firmly in position on high speed Pick & Place systems. It deploys the company’s proven low-voiding, thermally stable flux technology to guarantee a strong wetting force between molten solder and pad areas. This force is maintained throughout the entire reflow cycle to eliminate de-wetting tendencies and thereby eliminate the likelihood of open circuit interconnections arising from the warping force of the package.“Increasingly in BGA PoP applications, we see the devices are getting thinner to minimise overall component height, and this makes them more prone to warping during reflow,” explains Peter Martin, MD of Almit. In PoP assembly, the first device is placed into wet solder paste on the PCB. The next device to be stacked is typically dipped into gel flux and then placed on top of the first. Here, LFM 48 N delivers superior performance and greater reliability, especially where warpage during reflow of the first device impacts the ability of the solder balls on the underside of the second device to reflow successfully across an enlarged gap. “Using a dipping paste rather than just a flux simply adds more paste to the process and guarantees a better joint,” Martin points out. Almit’s new no-clean, lead-free LFM 48 N dipping paste formulation comprises Sn96.5/Ag3.0/ Cu0.5 with a solder powder size of 4 to 24 microns. It features a designed Open Time in a dipping tray of eight hours (at 23 °C & 50 % RH) and up to eight hours process window time between dipping and reflow.
EPP Europe 426
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