What is a micro-BGA?
The µBGA is a package that uses much smaller bumps than the traditional BGA. Usual solder balls are 500 to 700µm in diameter with a 400 to 500µm pitch, while a µBGA pitch is much smaller, reaching 150µm or less. µBGAs are key for industries where miniaturization is a driver such as automotive, mobile phones and computers. In the medical device industry too, more functionalities and enhanced power in reduced form factors is setting the trend in the race for innovative portable, wearable, and connected applications.
Pitch size is defined as the distance between consecutive balls on a BGA package, measured from center to center.
Why is Flip-Chip preferred over Wires in µBGA bonding?
The term “flip-chip” refers to an IC that is mounted directly onto a substrate or board in a “face-down” manner. Electrical connection is achieved through conductive bumps built on the surface of the chips, which is why the mounting process is “face-down” in nature. During mounting, the chip is flipped on the substrate or board with the bumps being precisely positioned on their target locations. Because flip chips do not require wire bonding, their size (both lateral and vertical) is much smaller than their conventional counterparts.
Scheme of a µFCBGA
What are the challenges with µFCBGA assemblies?
Because of the BGA’s very fine pitch, very small pad sizes, and high I/O count, extremely accurate placement is necessary to achieve maximum mechanical contact and minimize assembly defects. Assembling a printed circuit board (PCB) with ball-grid array (BGA) requires the utmost precision, especially in the case of micro-BGAs. Component placement tolerances must be very tight to obtain highly reliable solder joints. Accurate solder paste stencils, the choice of the right solder paste, and finetuning of the reflow process also play a critical role in avoiding solder defects such as voiding. And last but not least, adapted test solutions are required for such high-density components. Besides the required X-Ray inspection, a strategy has to be implemented for electrical and/or functional tests.
Next Issue – Valtronic Case study
Manufacturing of Micro-FCBGA with 2100 connections and a pitch of 150µm.