晶圆级芯片级封装的背面保护

Wafer-level chip scale packages (WLCSPs) certainly rank among the key enablers of smaller, thinner,  higher functionality devices that are driving advances in mobility, integration and expansive connectivity  (IoT). Undoubtedly, the mobile phone and tablet markets have been the primary catalyst for the growth  in WLSCP packages in recent years, though there are several other applications that benefit from the  thinner, higher-density ball count capabilities of modern-day WLCPS. No doubt mobile phones and tablets  will remain important consumers of WLCSPs, but the trend toward prolific connectivity through wearable  devices, among other technologies, will help fuel the 6-7% [1] annual growth rate projected for WLCSPs  over the next five years.

With the decreasing dimensions and finer ball pitches come increasing wafer processing and handling  challenges. Die chipping, die cracking, wafer warpage and package damage during the SMT placement  process onto the PCB substrate are all potential obstacles that have to be overcome for high-yield WLCSP  production. Recent advances in film technology have resulted a class of materials that help alleviate  some of the traditional WLCSP handling and reliability challenges. Backside protection (BSP) films offer  packaging subcontractors a technique that helps reduce mechanical damage, while improving laser  marking performance and reliability.

Some of the more notable semiconductor packaging film innovations in recent years have come from  Henkel. The industry’s first conductive die attach films were introduced by the materials leader almost a  decade ago, while other significant film successes include thermal formulations and non-conductive die  attach materials. Leveraging the company’s know-how in film formulation, Henkel has developed a series  of Backside Protection (BSP) films to enable production of today’s WLCSP devices. With advantages over  other commercialized BSP materials, Henkel’s LOCTITE ABLESTIK BSP 1000 is facilitating production of  today’s highly miniaturized (< 5 mm x 5 mm) WLCSP devices.

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Currently available in three different standard thicknesses* -- 25 µm, 40 µm and 100 µm – LOCTITE  ABLESTIK BSP 1000 can accommodate various bondline requirements and helps eliminate the need for  subsequent mold compound processes. The material is black in color, which not only promotes high  visibility of laser markings, but also serves to block light and provide surface protection, helping to keep  the circuit surface free from any handling damage.

One of LOCTITE ABLESTIK BSP 1000’s primary competitive advantages is its excellent reworkability on both  8” and 12” wafers. In the event that the film needs to be removed from the wafer, LOCTITE ABLESTIK BSP  1000 is easily peeled off the wafer, leaving no residue. The packaging subcontractor can then reapply the  film as per the process noted above. In testing, competitive materials -- particularly with respect to 12”  wafers -- have shown removal difficulty which can result in wafer damage or the requirement for  subsequent cleaning steps.

As for its laser marking clarity, LOCTITE ABLESTIK BSP 1000 has exhibited excellent laser marking  performance both prior to cure and after reflow, as shown below. This is critical, as the device ID is  essential to inventory management, quality control and process tracking.