Every FPGA is a ball grid array, and the joint under that array is where an FPGA board succeeds or fails. A modern high-end FPGA can carry well over a thousand solder balls on a fine pitch, hidden entirely beneath a package with a large thermal mass. There is no way to see those joints by eye, no way to touch them up casually, and no cheap way to recover if they are wrong, because the device on top may cost hundreds or thousands of dollars. FPGA BGA assembly is the single most demanding step in building FPGA hardware, and it is the step FPGA.io is built around.
This page explains what makes FPGA BGAs so difficult, how a controlled BGA assembly process removes the risk, and what X-ray inspection, rework, reballing and moisture control actually contribute to a reliable board.
What makes FPGA BGAs so challenging
A ball grid array trades visible, inspectable leads for a dense grid of solder balls under the package. That trade buys enormous I/O density, which is exactly why FPGAs use it, but it concentrates several hard problems into one component.
- Very high ball counts. Large AMD (Xilinx) and Altera FPGAs frequently have 900, 1156, 1517 or more balls. Every one of those joints has to form correctly, at the same time, under a part you cannot see beneath.
- Fine pitch. FPGA and companion-device packages run from 1.0 mm down to 0.8 mm, 0.5 mm and 0.4 mm pitch. As pitch shrinks, the margin between a good joint and a bridge shrinks with it, and paste printing and placement tolerances tighten dramatically.
- Package warpage. Large packages flex as they heat and cool during reflow. If the corners lift while the centre stays down, or vice versa, you get opens or the notorious head-in-pillow defect where a ball touches the pad but never coalesces. Controlling warpage is central to a good result.
- High thermal mass. A big FPGA absorbs a lot of heat. The reflow profile has to bring the balls at the centre of the array fully molten without cooking the small passives at the board’s edge, a balancing act that a generic profile rarely gets right.
- Hidden joints. Because you cannot optically inspect under the package, the only way to verify the array is X-ray. Assembly you cannot verify is assembly you cannot trust.
None of these problems is exotic on an FPGA board, they are the everyday reality of the parts, which is why process discipline matters so much more here than on a simple SMT board.
BGA package types we assemble
FPGA hardware brings a wide range of bottom-terminated packages, and each has its own handling considerations. Our BGA line assembles the full range you are likely to design in:
| Package type | Typical use on FPGA boards |
| Standard BGA / PBGA | The FPGA itself and large companion devices |
| Fine-pitch BGA (0.5 / 0.4 mm) | High-density FPGAs, memory, and SoC companions |
| micro-BGA / CSP | Power management, memory, and small logic |
| LGA and QFN / bottom-terminated | Regulators, RF front-ends, sensors |
| Package-on-package (PoP) | Stacked memory-on-processor configurations |
Whatever mix your board carries, the same principle applies: the joints are hidden, so the process and the inspection have to be good enough that hidden does not mean unknown.
Reflow process control: profiles, nitrogen and warpage
The heart of reliable BGA assembly is the reflow profile, and on FPGA boards it is developed per board rather than pulled from a library. The profile has to account for the FPGA’s thermal mass, the copper planes acting as heat sinks, the smallest and most heat-sensitive parts on the board, and the warpage behaviour of the largest packages.
Several controls come together to get it right:
- Board-specific thermal profiling. We profile the assembly with thermocouples so the balls at the centre of a large array reach full reflow while edge components stay within their limits. This is the difference between a joint that coalesces and one that does not.
- Nitrogen reflow. An inert atmosphere improves wetting and reduces oxidation, which helps fine-pitch and high-ball-count devices form clean joints and lowers the risk of head-in-pillow.
- Warpage management. Correct ramp rates and peak control, matched to the package’s known warpage behaviour, keep the array flat enough for every ball to make and hold contact through cool-down.
- Solder paste and stencil control. Fine-pitch BGAs are unforgiving about paste volume. We combine an appropriate stencil design with solder paste inspection so the right amount of paste is in the right place before the FPGA is ever set down.
Get the profile right and a thousand-ball device solders cleanly and repeatably. Get it wrong and you chase intermittent, hard-to-find failures that only X-ray will reveal, which is exactly why the next step exists.
100% X-ray inspection: seeing what you cannot see
Because BGA joints are hidden under the package, X-ray inspection is the only way to confirm them, and on FPGA boards we inspect 100% of BGAs, not a sample. X-ray reveals the defects that optical inspection physically cannot:
- Voids inside the solder balls, which can compromise the electrical and thermal path if they are large or badly placed.
- Bridges between adjacent balls on fine-pitch devices, a short you would otherwise only find when the board fails to power up correctly.
- Head-in-pillow, where a ball and the paste never merge into one joint, an intermittent failure that is extremely hard to diagnose any other way.
- Missing, insufficient, or misaligned balls, and open joints at the corners of a warped package.
For the highest-reliability programs, we can also perform cross-sectioning or computed-tomography analysis to characterise joint quality in depth. The principle is constant: a BGA joint you have not verified is a risk you are shipping, and on a board carrying expensive FPGAs that is a risk worth eliminating outright.
BGA rework and reballing
Even with a strong process, prototypes and field returns sometimes need a device removed and replaced, and on an FPGA board that is delicate, high-value work. A large BGA cannot simply be reflowed off with a hot-air gun without risking the board, the neighbouring parts, and the device itself.
Our BGA rework capability covers the full cycle done properly:
- Controlled removal of the BGA with localised, profiled heating that protects the board and adjacent components.
- Site preparation, cleaning and dressing the pads so the replacement has a clean, planar surface to sit on.
- Reballing, restoring a fresh, uniform ball array to a device that has been removed, so a costly FPGA can be recovered and reused rather than scrapped.
- Precision re-placement with alignment optics and a controlled reflow, followed by X-ray verification of the new joints.
The ability to remove, reball, and re-place a large FPGA reliably is what saves the part when a board needs correction. On a device worth hundreds or thousands of dollars, that recovery is often the difference between a minor rework and a scrapped assembly, and it is a capability generic assembly houses frequently do not have.
Moisture-sensitive device (MSD) management
Large FPGAs and their BGA companions are almost always moisture-sensitive, commonly rated at moisture sensitivity level (MSL) 3 or 4. If a moisture-laden package is reflowed without proper handling, absorbed moisture flashes to steam and can crack the package or delaminate it internally, the failure known as “popcorning,” and it can ruin an expensive device invisibly.
We manage MSD parts to J-STD-033: controlled storage in dry conditions, floor-life tracking once packages are opened, and baking to remove absorbed moisture before reflow when required. On FPGA boards this discipline directly protects the most valuable component on the assembly, and skipping it is a quiet way to lose parts you have already paid a premium to source through reliable channels.
Underfill and long-term reliability
For assemblies that face mechanical shock, vibration, or thermal cycling, in automotive, aerospace, industrial, and rugged applications, underfill can be applied beneath the BGA to bond the package to the board and share mechanical stress across the whole footprint rather than concentrating it on the corner balls. This substantially improves the mechanical reliability of large packages in harsh environments. We advise on whether underfill is warranted for your application and apply it as part of the assembly when it is, because on a big FPGA the corner joints are exactly where fatigue failures start.
Why FPGA.io for BGA assembly
BGA assembly is where a specialist earns its keep. A generic PCBA shop can place a BGA, but FPGA boards demand board-specific reflow development, 100% X-ray verification, and the rework and reballing skills to recover expensive devices when something needs correction, all applied to parts that leave no room for guesswork. That combination is exactly what we concentrate on, and it is why teams building serious FPGA hardware bring their toughest boards here. From a first prototype of a new Altera or Xilinx design to a qualified production line, the BGAs are placed, inspected, and, when needed, recovered by people who do this every day.
Frequently asked questions
What is the finest BGA pitch you can assemble?
We assemble down to 0.4 mm pitch, covering the fine-pitch FPGAs, memory, and companion devices used on modern boards. Very fine pitch places tight demands on paste printing and placement, which our process and SPI are set up to meet.
Do you X-ray every BGA?
Yes. On FPGA boards we X-ray 100% of BGAs, because the joints are hidden and X-ray is the only way to verify them. We check for voids, bridges, head-in-pillow, and open or misaligned balls.
Can you rework or replace a BGA on my board?
Yes. We remove, prepare the site, reball where needed, re-place, and X-ray-verify BGAs, including large FPGAs. This lets a valuable device be recovered rather than scrapped when a board needs correction.
What is head-in-pillow and how do you prevent it?
Head-in-pillow is a defect where the ball and the solder paste touch but never merge into a single joint, often caused by warpage or oxidation. We prevent it with board-specific reflow profiling, nitrogen reflow, and controlled warpage management, and we detect it with X-ray.
How do you handle moisture-sensitive FPGAs?
We follow J-STD-033: dry storage, floor-life tracking after packages are opened, and pre-reflow baking when required, so moisture-sensitive FPGAs are not damaged during assembly.
Can you do BGA assembly for just one prototype?
Yes. We assemble single prototypes as well as volume production, with the same X-ray verification on every BGA regardless of quantity.
Get an FPGA BGA assembly quote
Send us your board files and BOM and we will quote your BGA assembly, typically within 24 hours, with 100% X-ray inspection and a free manufacturability review included, so hidden defects never become field failures.
➜ Request a BGA assembly quote
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