All About BGAs – Why Are BGA Rework Stencil Kits So Important to BGA Chips?

As chip packing technology goes from one strength to another, BGA (ball grid array) has become the perfect form of packaging for devices manufactured using surface-mount technology (SMT). BGA is now one of the standard packaging techniques in the industry. Anyone involved in the manufacture of electrical chips and devices must know everything about BGAs, including how to rework them when things go wrong.

 

 

A Brief Understanding of the BGA Process  

·         BGA is a surface mount package consisting of arrays of metal-alloy balls at the bottom (usually made of Tin, Silver, or Copper).

·         These metal-alloy balls at the bottom of the package are soldered onto a PCB (printed circuit board) to create functioning electrical connections.

·         The array or grid of metal alloy balls makes this package very space-efficient. It’s possible to create as many connections as the number of metal alloy balls on the package.

·         These interconnection pins are always located below the packages, not on their side. Hence, integrated circuits have more interconnects despite having lesser space on the Printed Circuit Boards (lesser compared to other packaging methods).

·         An Integrated Circuit (IC) created using the BGA technique will consist of chips or processors that are attached to the substrates. The IC’s die is connected through a wire and to the slabs. Solder balls are attached on the opposite side of the substrate. This package is then soldered onto a PCB and ready to be used.

For smaller electrical devices created using SMT (known as Surface Mount Devices or SMDs), BGA packaging is absolutely crucial. BGA surface array packaging techniques have been researched since the 1960s.

However, this SMD packaging technology first took off in 1989 when Motorola and Citizen developed the first plastic SMD packages. Since then, the application of BGA has been significantly encouraged by all industry professionals for various reasons –

 

·         BGA packages are used in most of the world’s telecommunication products, computer systems, and workstations.

·         The average assembly defect rate of BGA chips is only 0.3 parts per million. Even if the assembly defect rate was as high as five parts per million, it would appear as if the entire manufacturing cycle took place with essentially no defects.

·         When BGAs are being soldered onto PCBs, the solder balls only require heating to melt and stay stuck to the PCB. The risks of component damage are minimal, and just the surface tension between the PCBs and the solder balls is strong enough to keep the package strongly attached. In other techniques like pin grid arrays (PGA), the chances of damaging the components are much higher as the soldering process isn’t as straightforward.

·         In the PGA technique, individual pins require a lot of care as they’re fragile and can be easily bent or reshaped. In the BGA technique, solder balls, and solder pads on the PCBs form super-strong connections making the packages extremely robust and reliable to motion-caused damages.

·         Thanks to the tightly-knit grid arrays of all the connections inside BGAs, the connections are shorter. Hence, high-quality performances at super-high speeds are guaranteed.

 

 

However, the metal alloy balls are extremely inflexible, plus BGA packages are, in general oddly-shaped. These factors make BGA package chips far from perfect. If these chips aren’t soldered properly, the risk of short circuits is always large. Here are the drawbacks of BGAs –

 

 

·         The strong bonds between PCBs and the components can often lead to physical stress, which is converted into efficiency issues.

·         Since the PCBs and the components are soldered very tightly, it’s hard to inspect these packages manually. To even detect defects, soldering professionals have to melt the device and replace the BGA.  

·         The average pad size of BGA chips is somewhere between 18 millimeters to 25 millimeters; hence soldering is very difficult.

·         Soldering professionals have to create accurate fiducial marks just for inspection purposes. It’s impossible to inspect the tightly bound solder joints with naked eyes, so the fiducial marks serve as easily readable notifiers.

·         Overuse causes solder joints in-between the chips and the PCBs to loosen, causing short circuits. Such BGA chips either need replacing or upgrades – both are tedious processes.  

·         Some faults, such as the overeating of solder balls leading to the creation of solder bridges are extremely common.

 

All of these risks are why rebelling and rework are two common themes whenever BGA chips are mentioned. Let’s learn about these processes.

BGA Rework – What is It?  

Reworking a BGA involves changing all or some of the soldered balls on the BGA chips. If the balls on BGAs aren’t creating accurate connections between the chips and the PCBs (because of overuse, heating, etc.), the ball solder joints need to be recreated by soldering professionals.

 

 

To carry out BGA rework processes, soldering professionals will need – soldering irons, soldering paste, de-soldering wires, new BGA chip cases, and most importantly – a BGA reworks stencil kit. These kits come with BGA chip stencils that help soldering professionals get the BGA to rework the process started in the most accurate way possible. These stencils (made of high-quality steel) help soldering professionals apply solder paste accurately.