The most important and difficult aspect of printed circuit board (PCB) designs using fine pitch BGAs is the layout of their lands and fan-outs. Pitch is defined as the space between the center of one BGA ball to the center of the next one. Micro BGAs with 0.3 mm pitch BGAs are found in virtually every smartphone. And 0.2 mm ultra-fine pitch BGAs are steadily moving into next generation products.
PCB lands are where device balls sit and get soldered to. Fan-outs are traces from the device lands to adjacent via. A via is required to distribute the I/Os, powers and grounds from the device to the peripherals and typically there is one via per land, as shown in Fig. 1.
Solder-masked-defined (SMD) pads are used for devices that have 0.5mm or finer pitches. Design missteps incurred at PCB layout when the designer innocently takes the 0.5mm pitch design route can have adverse effects on board fabrication and assembly. The reason is 0.5mm pitch design guidelines differ from fine pitch design guidelines.
A wide range of issues arises in those areas to include problems associated with stencils, solder paste, and pick and place, among others. In particular, the designer must be aware of the current manufacturing capabilities in addition to the PCB’s electrical requirements.
Read our EE Times article for more details.
In the meantime, here are some tips and hints to get you better acquainted with fine pitch BGA design.
- For 0.5mm pitches or greater, non-solder-mask-defined (NSMD) pads for devices are generally preferred.
- In the case of 0.3mm pitch devices, if the same guidelines are used, it can lead to potential failures during manufacturing or in the field.
- Solder-masked-define (SMD) pads for 0.3mm pitch devices allow more solder areas on the BGA pad so that solder shorts are less likely.
- Routing guidelines for PCBs populated with fine pitch BGAs represent a key area demanding special layout consideration.
- SMD pads benefits include solder mask protection to any traces routed between the lands.
- For 0.2mm ultra-fine pitch BGA design, it is strongly advised to use via-in-pad technology since there is no room to perform a dog-bone type fan-out.
It is safe to predict there’s an increasing need of more processing power in products like wearables, IoT devices, and embedded medical devices. Even though phones and tablets may have stabilized in size and the trend is more toward system on chip (SoC) than it is toward more shrinking, we definitely will be seeing more chips with pitches of 0.3mm and less.