Having a pitch of 0.5mm and more, generally, we recommend that you use non-solder mask define pads for your ball grid arrays. This pad will ensure better adhesion as regards the ability of the solder to hold the copper sides as well as the topmost surface. With respect to BGA 0.5 mm pitch, majority of part manufacturers still prefer to use NSMD pass.
If granted, there is a need to ensure that the fab house has the ability to perform well when it has to do with mask registration. There’s nothing good about having pads which are part (half) NSMD and part (half) SMD. Of course, we have seen that.
As soon as you reach the BGA 0.4 mm pitch, things will likely get different. Of course, we have started seeing more of these happening. In some wafer scale package (WSP) or chip scale package (CSL), LGA and BGA parts have started showing up in the BGA 0.4 mm pitch, and some larger parts such as the OMAP processor
Furthermore, at this size, you’ll start seeing more risks associated with solder bridging with respect to NSMD pads. With small geometries, routing the escape traces on the topmost layer will not be possible as well. The pad has to be a solid metal with no exceptions. Avoid making use of a solder mask in capping the vias present at this pitch too. Make sure it is all metal.
Breaking out a BGA 0.4 mm Pitch
One thing all designers of printed circuit boards will agree on is that breaking out a BGA requires discipline and precision. When breaking out a ball grid array, you are applying a fanout solution. Then you will route the traces from the fanouts to the device’s perimeter before the PCB’s general routing. Below are two illustrations on a BGA 0.4 mm pitch breakout.
BGA 0.4 mm Pitch Breakout
To become a printed circuit board master for HDI begins with gaining knowledge on the breaking out of a BGA. Note that ball grid arrays (BGAs) are known to possess the largest density of array pins and I/O connections on a specific device. Regarding the layout, this part is very complex.
Since breaking out a BGA can be done in many ways, we will be teaching you with an example the process involved in breaking out a BGA 0.4 mm pitch. To ensure a great design practice, there’s a need to handle the layout systematically. You have to ensure that you can fanout, as well as connect the pads with the BGA. Drawing of short tracks is another great design practice.
Before you go ahead with breaking out a BGA 0.4 mm pitch, you have to consider the overall size as well as the pin out of that part. This way it becomes possible to make use of a technology that is very cost efficient.
To fan out a BGA 0.4 mm pitch, this geometry doesn’t work out to help you route traces in-between the pins. Furthermore, the gaps and traces are usually very small to reach enough layers and then get the pins all fanned out.
Therefore, for a BGA 0.4 mm pitch, you will need a buried and blind vias. The routing of the pins present on the BGA’s outermost row will be on Layer 1, while those on the following row will be on Layer 2. The way in which the BGA pins out determines the routing of the BGA.
Example 1: Breaking out a BGA 0.4 mm Pitch
This is a standard BGA 0.4 mm pitch. The most appropriate way of fanning it is making use of a blind and buried vias. You begin by adding the layer 1 to the layer 2 blind via on the entire BGA’s GND pins. Now you have completed the job with the GND pins, and so there is no need to do the routing.
Drill and Pad Sizes for BGA 0.4 mm Pitch
Traces will be absent between the top layer pads. So, these pads could be 10 mils and then feature between them a 5.7 gap. Concerning the larger pads, allow the manufacturer to drill a laser drill of 4 to 5 mil for the blind and buried vias.
Also, the distance in-between the layers of the board have a huge role to play in the drill size. This will make it possible to shut the hole and then produce a flat pad to work with the BGA.
Sequential Lamination
Now, let’s say this board has 8 layers. You will laminate the second to the seventh layer together. From layer 2 to layer 3, you can make use of laser drill. Note that this will be your two to three 3 buried via. Also, take note that it is possible to use a buried via of layer seven to six. This also holds for layer two to layer 7. However, there’s a need for the two to seven to have a larger pad and drill.
The first and eighth board layers will now undergo lamination on the board. Also, you will conduct a laser drill from the first layer to the second layer. If needed, you can also do the tenth to the ninth layer.
Example 2: Breaking out a BGA 0.4 mm Pitch
Here, we are dealing with a BGA 0.4 mm Pitch on a 6 by 6 matrix. Its space/trace is 4 to 5 mil, with 8-mil pads and 4-mil lasers. Furthermore, the routing strategy features staggered and stacked vias.
Also, the PCB features 4-mil vias. Furthermore, the thickness of the material between the first and second layers has to be a maximum of 4 mils. The rule for the aspect ratio requires a dielectric of 4 mils between the first and second layers. Also, you must keep the stackups symmetrical.
Conclusion
We hope we have explained to you how to breakout a BGA 0.4 mm pitch. To have a full understanding, we advise that you read it over again. Please feel free to ask you questions if you have any.
