Playstation 4 has a major component called APU, it hosts CPU and GPU inside of itself. This component is the powerhouse of your game console and processes all the information. It is soldered onto the board using multiple connections. This type of SMT mounting is called BGA.

What is PS4 reballing?

Playstation 4 has a major component called APU (Accelerated Processing Unit), it hosts CPU and GPU inside of itself and is developed by AMD in cooperation with Sony. It is actually manufactured by TSMC using 28nm manufacturing process. This component is the powerhouse of your game console and processes all the information as well as acts as graphics card for your PS4 to output all the video on your screen.

It is soldered onto the board using multiple connections, which sit in between the APU integrated circuit and the board. These connections are made out of solder and serve 2 purposes: provides physical mounting to the component as well as electrical connectivity to the board. This type of SMT mounting is called BGA, it stands for Ball Grid Array. As this ball grid array is made completely out of hundreds tiny solder alloy connections they tend to fail from time to time, mostly due to a such high population of them and due heat cycles your PS4 is exposed to during gaming.

This APU is extremely powerful and we all know powerful components on circuit boards do tend to run quite hot. APU is cooled down by a heatsink and fan, however, within itself it still operates at temperatures up to 90C. The problem lies when the substrate temperature is raised and the material expands, however, when console is powered down temperature reduces and all the components retract back to their original positions. Of course, we are talking micro levels here and you won’t see this actual expansion happening. This expansion and retraction isn’t healthy for solder joints and once we add factors, such as moisture accumulation in the air as well as dust contamination these little solder spheres tend to fail by developing micro cracks within ball grid array.

Even if any one of these connections fail, and there are hundreds of them, APU loses its connectivity to the circuit board and your PS4 usually does not turn on at all or malfunctions. Sometimes this will produce artefacts on the screen or video freezes during gaming session.

Playstation 4 reballing procedure means we replace all these solder joints between SoC (System on Chip) and printed circuit board. New fresh solder spheres re-establish that lost connection and obviously the game console comes back to life. During reballing procedure we remove the component, in this case PS4 APU, clean all the old solder from circuit board and component, place new spheres on and solder it back on board. These are the essential steps of any BGA reballing procedure.

However, to do it professionally and ensure the process is scale-able we have ensure factors such as moisture sensitivity, environmental temperature and ESD precautions are taken into consideration when working with developing complicated soldering procedures. We also have to ensure the process is carried out in the clean environment as any kind of dust particles can interfere with soldering process. It is also recommended to introduce numerous quality control steps during the BGA reballing procedure as this will provide additional verification in case of errors, such as solder mask damage, solderability or contamination issues.

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Step 1 – Prebaking

Playstation 4 Reballing Procedure - Prebaking
Playstation 4 Reballing Procedure - Prebaking

Before we do any kind of soldering work on flip-chip design components, or actually any BGA, QFN, CSP devices that require complete reflow, it is required to carry out procedure known as pre-baking. The mentioned devices are sensitive to moisture, and we don’t mean they will fail if submerged in water… The built up of moisture adsorbed from environment is crucial to understand. As it is a well-known fact from physics that water turns into gas when heated and changes in volume. This exact effect, at micro levels, happens inside the substrate layers of printed circuit boards and Playstation 4 ASICs (Application Specific Integrated Circuits). As we need to melt the solder alloy, in order to remove PS4 APU, the temperatures will have to be increased to nearly 250C, which is way above water boiling temperature. We somehow have to eliminate this moisture as if trapped inside and heated it will expand in volume and look to escape. This will crack the substrate and damage the component or even a circuit board. This water boiling, changing its volume when turning into steam and cracking the structure is known as delamination. Also called “popcorning” as you can actually hear it making an audible sound, similar to the popcorn popping.

To get rid of this of this risk we have to eliminate the moisture completely from the board. That’s when pre-baking comes in. It is a process when we increasingly raise the temperature of the board and components just above water boiling temperature and keep it there for extending period of time. This allows moisture to be eliminated at controlled / slower pace. The process is usually completed within environmental ovens for a period between 24 and 48 hours.

Once we have the board prebaked we have 8 hours to carry out all the necessary work before we would have to pre-bake the board again. It is not, however, suggested to pre-bake the boards multiple times as this reduces ENIG surface solderability.

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Step 2 – De-soldering and cleaning board and IC

To refurbish BGA connections we have to remove the component completely from the board. We do this by targeting BGA and raising temperature of that solder alloy to its melting point so we could remove it while it’s liquid. As all of these connections are hidden away underneath the component, it means the whole component will have to be heated to around 225C in order to melt these joints. Now we can’t just apply heat directly to this area as it will damage the APU component. This is where reflow soldering profiles come into play. We have to use a rework station, which can run a soldering profile meaning it can heat up the targeted component at a pre-programmed pace. This will ensure the least amount of stress is caused to the substrates.

The soldering profile usually consists of 4 stages with different rates of heat radiation. It has to be fast enough to minimise the time component spends at extreme temperatures, however, long enough to safely raise the temperature for solder alloy to become liquid, the key point here is safely. This soldering profile is custom and has to be developed before it can be integrated into production level repairs. It means we most likely cannot re-use these soldering profiles for different rework stations or different boards. There are, however, some guidelines of what usual reflow profile can look like. Lead free solder alloy profile would have 4 stages: preheat, soak, reflow, cooling. These stages all have different rates of raising the temperature of the targeted area so we could reflow BGA solder spheres.

In order to remove the component we have to mount the board on the rework station. It has to be mounted and supported to avoid sagging or bowing during heating stage. If we leave the board unsupported, heated circuit board fiberglass will flex and could develop cracks on other component solder joints, which would be hard to identify and rectify.

Once mounted, the board will be heated from the top and bottom. We will be heating the board from underneath to around 160C to as this will help to control inner copper planes expansion levels. Keeping substrate expansion levels at the same rate across the whole board will help to avoid delamination. Once we have the board preheated we increase the intensity of the top heater to target the area where BGA is located and completely melt the solder alloy. We then have a 10-15s window to pick up the component. This is done using vacuum suction system. Monitoring the whole process using camera helps to ensure that solder spheres have melted all around the actual BGA site. Great care has to be taken when lifting component. In an attempt to pick up the component while not all solder spheres are liquid will cause serious damage to BGA pads, which most of the time are not economical to repair.

Cleaning all that residual old solder requires specialised soldering equipment. To clean the board we would use the soldering iron tip with wide tunnel type tip. To ensure we do not cause stress, it is recommended to preheat the board temperature to around 140C and keep it within this range, whilst cleaning. The skill during cleaning is to minimise the temperature and the amount of strokes it requires to completely clean BGA pads and re-tin them to revive that solderability back into these oxidized pads. De-soldering wick is usually used to adsorb all the solder from the pads. Once the solder is removed the excess flux is cleaned using variations of de-fluxers and IPA.

Playstation 4 Reballing Procedure - Cleaning BGA Site

Same procedure has to be performed for a PS4 APU, which in this case has to be mounted in a special jig. To help remove residual solder we can use another alloy with possibly lower melting point, which will allow easier flow of that lead free solder. Once residual solder is removed, it is safe to clean PS4 ASIC using ultrasonic cleaner as it is flip-chip design IC unlike wire-bond technology ICs.

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Step 3 – Reballing and IC reflow

Now that we have removed PS4 APU and cleaned the board, the IC is ready for actual reballing procedure. This process will place new solder spheres on the component and reflow them on the component side. This is done using reballing fixtures, stencils and dedicated reballing oven. We are using 0.5mm solder preforms to reball this ASIC and place them using a stencil. This stencil is specifically designed to fit reballing fixtures and has apertures wide enough to accommodate solder spheres. The stencil also has to be thick enough to ensure pre-forms roll into place and stay there, however, thin enough to ensure it does not act as a heatsink during reflow.

Playstation 4 Reballing Procedure - Reballing
Playstation 4 Reballing Procedure - Reballing

Once all spheres are placed and inspected they have to be soldered on to the component. The process actually melts all these little solder spheres on the BGA pads. Again, same rules apply, the profile has to be created considering new solder alloy properties as well as component heat absorption rates. These reballing ovens act as mini rework stations and create safe and repeatable environment around the component, which is crucial when working on such complicated soldering procedures. Using this method allows us to automate reballing process and ensure we achieve successful result each and every time.

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Step 4 – Placement and soldering

At the next stage we introduce the first quality control step, which evaluates the condition of the PCB and reballed PS4 APU to ensure no damage or contamination occurred up until now. Things we look for are:

  • Discoloured pads, which can cause solderability issues;

  • Foreign particles, such as dust or lint;

  • Solder mask damage, which causes solder joint starvation;

  • Cratering on the solder spheres, caused by overheated alloy;

  • Alignment of ball grid array, as even slight misalignment can cause solder bridges later.

The inspection is carried out under microscopes.

Once we are happy with all the inspection results and the condition of the solder mask of both BGA sites, we are ready to place and solder the component on the board. Board is mounted on the soldering rework station in the same way as during the removal of APU. Now, in order for us to mount the PS4 ASIC on BGA site precisely we need to use a mechanism called split vision positioning system.

Playstation 4 Reballing Procedure - IC Inspection
Playstation 4 Reballing Procedure - Soldering
Playstation 4 Reballing Procedure - Soldering

This system consists of 2 different cameras and a monitor. Having 2 feeds from the bottom of the component and the top of the PCB allows us to align component precisely on the BGA pads using micro adjustment levers. We can also zoom in and adjust the contrast of each image to really get in there and align it perfectly.

Once aligned, the component is automatically lowered into place using vacuum suction system. The sensors within rework station allow easy placement, as it automatically stops when force-back is detected.

When it comes to reflowing / soldering component back into place, we most certainly cannot use the same reflow profile we used during removal. New soldering profile has to be developed, which runs according to the characteristics of the new solder spheres placed on the APU BGA. Once profile is running we are able to monitor the process on screen with cameras at macro level. This allows us to really see how the solder behaves and we can actually see when component finishes reflow as it levels itself into place once all solder is liquefied. Again, during development of this soldering profile we have to make sure factors, such as environmental exposure and already existing heat cycles are taken into consideration to ensure the profile is safe enough to carry out the soldering procedure successfully.

Cooling of the soldered board cannot be overlooked either and has to be completed at recommended 5C per second down curve to minimise thermal shock, as this can cause solder joints to become brittle and develop cracks.

As we have used flux to help with oxidation when soldering, it has to be carefully cleaned. And we always like to make any of our soldering procedures presentable and tidy.

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Step 5 – Prism inspection

Playstation 4 Reballing Procedure - IC Inspection

Post-reball quality inspection is one the most important steps during quality control. We inspect the BGA solder spheres using prism microscope, which allows to actually see underneath component and into the array. Factors, such as:

  • coplanarity,

  • solder ball shape,

  • bridges,

  • missing spheres,

  • bleeding,

  • solder mask damage

are evaluated to confirm PS4 BGA reballing went successfully.

Step 5 – Assembly and soak test

After that last step of quality control is finished the console is serviced by cleaning every single part and finally assembled back to go through a soak test. This soak test puts it under stress, whilst we monitor the temperature, which ensures we have successfully fixed the fault.

Once it passes stress testing it is then released to customer collection with our standard 3 months warranty.

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