Choosing the Right BGA Reballing Stencil

Ball grid arrays (BGAs) are an essential and complex component of electronics. They provide crucial thermal conductivity, package density and resistance to interference. Unfortunately, when they malfunction, they can be difficult to repair.

Contact between a chip and a PCB is often lost due to thermal damage or mechanical issues. In this case, the best way to restore BGA pins is through reballing. After the BGA is removed from the PCB, reballing is the process of putting all the pins on the BGA with the help of a soldering station. Once it has been reballed, the faulty chip may be used again, or the pins can be put on a new chip.

BGA stencils are critical tools for making the reballing process run smoother. They are designed to simplify the array device placement to save you as much as 50% of the time you would otherwise spend reworking your BGA.

Below, we've provided more information about how to select and use the right BGA reballing stencil for your unique needs.

Types of BGA Stencils

BGA stencils are essentially plates, typically made of metal with small holes in it. The size of the holes corresponds to the diameter of the BGA solder balls, and the spacing between the holes corresponds to the spacing between the pin surfaces of the chip. BGA stencils are available in two different types: specialized and universal.

Universal stencils are square matrices with holes that are all the same size. They're ideal for reballing chips with the same pitch and diameter as the stencil.

Specialized stencils are also square matrices, but their hole alignment is the same as the arrangement of pins on the chip. They are most often used in cases where the same type of chip must be regularly reballed.

Most reballing kits include a universal stencil, which tends to be the more popular stencil type.

How to Choose the Best BGA Reballing Stencils

You should keep several key considerations in mind when you're choosing your BGA stencils. First, you'll want to consider how resistant the stencil is to deformation during the heating process. Many stencils used for reballing computer chips are not heat-resistant, which means they should only be used for placing the balls, and they should be removed when the chip is heated.

You also need to know the sizing requirements for the BGA you're using so that you can ensure the solder balls are properly secured. These sizing requirements include the dimensions and thickness of the BGA.

How to Use BGA Stencils

To properly secure and use a BGA stencil, follow these steps:

1. After you've removed the BGA from the PCB, clean and prepare the stencil and your BGA stencil rework station. You can use isopropyl alcohol and a lint-free wipe to get rid of any dust or other contaminants.
2. Peel the adhesive off the back of the stencil and place it. To properly apply the stencil, align its holes with pins on the chip. Place the stencil down at one corner and work slowly to the opposite corner. Once it's been placed, gently smooth it down.
3. Next, you'll apply the solder paste. You should allow the solder paste to reach room temperature and stir it before applying. To apply, use a miniature squeegee or brush tool. Hold the tool at a 45-degree angle to the stencil and use just enough force to ensure that the solder paste sticks to the chip through the holes in the stencil.
4. Using your BGA stencil rework station, apply hot air to solidify the solder paste. This process will form solder balls that stick to the chip.
5. Remove any excess paste with a lint-free wipe, then inspect the work to ensure that the solder is evenly distributed.
6. Clean the chip with acetone or an IPA solution and remove it from the stencil.
7. The BGA can now be soldered back onto the PCB. Place the chip on the PCB and apply heat.

Benefits of Using BGA Stencils

With BGA stencil reballing, you will streamline the repair process and save yourself time. You can expect a low-cost repair method with precise results, even in tight or irregularly shaped areas.

When you use a BGA stencil that is correctly sized for your BGA, you'll improve your first-pass yields for greater overall accuracy and reduced scrap costs. The time required to align and place the device will also drop significantly.