Introduction to BGA Packages
BGA (Ball Grid Array) is a surface mount IC packaging method that utilizes a grid of solder balls on the underside of the package as electrical and mechanical connections. BGA packages offer several advantages:
- Higher input/output (I/O) density than other packaging types
- Smaller footprint than peripheral leaded packages
- Shorter electrical paths for improved performance
- Entire underside can be used for solder balls
However, BGA packages also introduce challenges for PCB rework and repair compared to through-hole components. This article provides an in-depth look at BGA rework and reballing processes and services.
BGA IC Package
Applications of BGA Packages
BGA packages are widely used for:
- Microprocessors and GPUs
- ASICs and FPGAs
- DSPs, microcontrollers and other ICs
- Memory chips including flash, DRAM and SRAM
- RF/microwave components
- High pin count logic and interface devices
- Automotive electronics
The high I/O density makes BGA an ideal package for complex ICs.
Challenges of BGA Rework
While BGA provides benefits, it also introduces unique repair challenges:
- Solder joints are hidden underneath package
- Small 0.5 to 1mm pitch between balls
- PC board pads are not accessible
- Not practical to repair individual solder joints
- Requires hot air or other specialized rework tools
- Risk of collateral damage around component
- Repair complexity increases with smaller BGAs
Professional BGA rework tools and services are often required to successfully replace or remove these components.
Reasons for BGA Rework and Removal
Common situations that require removing or replacing BGA components:
- Fixing defects introduced during PC board assembly
- Replacing damaged or faulty BGA components
- Upgrading firmware on a BGA microcontroller or flash IC
- Changing crypto keys on secure memory and controller chips
- Removing soldered components from circuit boards
- Salvaging components from discarded electronics
- Reworking prototype PC boards
Both repair facilities and electronics manufacturers routinely require BGA rework capabilities.
BGA Rework Process Overview
BGA component rework involves safely removing the component and then soldering the replacement using specialized tools and procedures.
Key Steps in BGA Rework Process
The overall BGA rework process consists of:
- Removal of defective BGA component from PCB
- Cleaning and preparation of board site
- Reballing the replacement component
- Precise soldering of new component
- Inspection and testing
Each step demands proper tools and techniques for reliable, damage-free rework.
Example BGA Rework Process
BGA Handling Dangers
BGAs require very careful handling to avoid damage:
- Never touch solder balls or board pads with fingers
- Avoid surface contamination or oxidation
- Prevent mechanical damage to solder spheres
- Use proper ESD procedures when handling ICs
- Keep components secured when transporting boards
Mishandling risks ruined solder joints or scratched pads resulting in rejection.
Proper tools, training and procedures are mandatory when reworking these sensitive components.
BGA Removal Methods
Removing an existing BGA involves heating to reflow the solder joints so the component can be lifted off without damage. Common removal methods include:
Hot Air Tool
A temperature-controlled hot air tool evenly heats the entire underside of the component simultaneously to avoid stressing the solder joints. Nitrogen protects against oxidation. The device is then vacuumed up.
Infrared Preheat + Hot Gas Tool
A combination of top-side infrared heating to bring the whole board up to temperature, supplemented with a hot gas nozzle to flood underneath the BGA provides very even, reliable heating for removal.
Conductive Hot Gas Tool
Instead of blowing hot air, nitrogen gas gets ionized into plasma which conducts heat into the board and component. This allows more heat while using lower temperatures to protect sensitive components nearby.
Vapor Phase Soldering
Condensing vapor phase heaters boil a liquid to create an even vapor blanket that envelopes the whole board and component to simultaneously reflow all joints.
In general, even, gentle heating is essential to avoid damaging boards or components during BGA removal.
Site Preparation and Cleaning
After removing the BGA, the board site must be cleaned and prepared for the new component:
- Removal of solder residue – Any solder left from the original joints should be cleared with solder wick and flux.
- Pad examination – Inspect for any scratches or damage to pads. May require pad repair.
- Reinforcement – Mechanical reinforcement of thinner boards around the BGA site may help avoid warping.
- Cleaning – Thoroughly clean site to remove all contaminants and debris for fresh soldering.
- Solder mask – Replace or repair any damaged solder mask areas around the site.
- Flux application – Flux should be applied to pads just before new component is placed.
Thorough preparation of the board area helps ensure successful replacement soldering.
BGA Reballing Methods
Before soldering, replacement BGAs often require “reballing” to attach new solder spheres using specialized equipment. Common reballing approaches include:
Solder Paste Stencils
Solder paste is screened or dispensed through a metal stencil matching the BGA footprint. The spheres adhere after placement and reflow.
Solder Jet Printers
Tiny solder droplets can be jetted onto each pad site. Allows very fine pitch placement. Reflow attaches balls.
Solder Ball Attach Tools
Pick and place tools can precisely attach individual pre-formed solder balls to the BGA footprint.
Flux Dip + Solder Bath
The BGA is dipped in flux and then upside down in a solder bath. Surface tension forms the ball grid array.
Reballing ensures proper solder spheres are present for forming connections to the new board.
BGA Placement Methods
Accurately aligning and placing the BGA component onto the board is critical for a successful rework. Common techniques include:
High Precision Optical Alignment
Machine vision cameras with optical magnification allow precise alignment of BGAs within +/- 0.02mm or better. Superior for ultra-fine pitch ICs.
Split Prism Alignment Tools
A split prism optical tool helps manually align the component to the board fiducials along both X and Y axes. Provides simple, low cost alignment.
Pick and Place Machines
Automated pick and place equipment can position BGAs very accurately by calibrating to board fiducial markers. Efficient for batches.
Adhesive Tacking
A small spot of flux or adhesive tack applied to the board center can hold the BGA in place during soldering.
Accurate alignment is essential to achieve the uniform solder fillet heights required for reliability.
BGA Attachment Methods
Proper heating and reflow methods are required to solder the new component without damaging boards or adjacent components. Common BGA attachment techniques:
Convection Oven
A thermal oven heats the entire board assembly to solder multiple components. Lower thermal gradients help avoid warping or cracking. Slow process.
Hot Air Soldering Tools
Focused, temperature-controlled hot air jets heat from the top side while a plate or jets heat underneath the BGA. Rapid, safe for nearby components.
Infrared Preheat + Hot Gas Tool
Combination of board preheating with infrared panels and pinpoint hot gas jets from below achieves fast, repeatable BGA soldering.
Vapor Phase Reflow
Boiling fluorinert liquid creates an inert vapor that completely and evenly envelopes the assembly for uniform soldering.
Laser + Underfill Preheating
A scanned carbon dioxide laser preheats the board while a secondary laser heats the substrate below the component. Underfill can be pre-applied.
Careful process control is mandatory during BGA attachment to form reliable solder joints without damage.
X-Ray Inspection
After reballing and soldering BGAs, x-ray inspection should be performed to validate solder joint integrity underneath the component:
X-ray image showing BGA solder joints
X-ray inspection can detect:
- Insufficient or excess solder
- Solder voids
- Poor wetting
- Misalignment issues
- Broken joints
- Foreign objects
- Solder balls missing or merged together
Catching defects under the package allows corrections before equipment leaves the factory.
BGA Rework Challenges
While essential, BGA rework and repair presents multiple challenges:
- Very tight pitch between balls, down below 0.4mm
- Small package sizes down to 5mm x 5mm
- Dense PCB and components obstruct access
- Nearby components sensitive to damage
- Warping of thin pc boards during heating
- Inspection only via x-ray for hidden joints
- Repeatable process control difficult
- High equipment and training costs
- Risk of collateral soldering damage
Extensive experience, training and the proper tools are required to successfully rework BGAs.
Advantages of Using a Rework Service
Given the equipment expense and technician skills required, specialized rework services can provide important advantages over attempting in-house:
Experienced Technicians – Consistent, high quality work only comes through extensive rework experience. Technicians must demonstrate proficiency across the wide variety BGA packages, board types, and unsoldering methods.
Specialized Equipment – Hundreds of thousands of dollars of tools like thermal profilers, microscopes, x-ray imagers, hot gas systems, and more. Impossible for low volume rework.
Process Validation – Documented procedures must be qualified through test vehicles with phase change analysis, shear force testing, and electrical verification.
Special Handling – Skills in handling tiny components, board warpage mitigation, ultra-fine pitch alignment, and micro soldering.
Economical – For lower volumes, utilizing services is far more economical than major equipment investments and tech training.
For companies without regular BGA rework, utilizing an expert service provider often proves the smartest option.
BGA Rework Process Checklist
The following checklist summarizes the key steps in a professional BGA rework process:
- Visual inspection of the board area and component
- Selection of proper removal method based on board and components
- Gentle, even heating of entire component and board to reflow for removal
- Vacuum pickup of removed component without damage
- Cleaning of board site with wick, cleaning solvents
- Inspection of pads for damage. Repair if needed.
- Flux application to pads just before new component
- Precise alignment of replacement component on board
- Reflow attachment soldering with even, thermal profile
- X-ray inspection of all solder joints under component
- Final visual inspection and as-needed rework
- Electrical testing for proper function
This rigorous process helps maximize first-pass rework success rates.
Establishing a BGA Rework Process
Companies establishing internal rework must consider several factors:
Staffing and Training
- Budget for dedicated, skilled BGA rework technicians
- Extensive hands-on training and certification
- Ongoing skills assessment
Facilities Requirements
- ESD-controlled workspace
- Thermal and humidity controlled
- Fume extraction
- Soldering tools require utilities
Equipment Needs
- Hot air soldering station with microscope
- X-ray imaging for inspection
- Soldering materials and chemicals
- Board holders, flip trays, tweezers
Process Definition
- Documenting processes for each BGA package and board type
- Creating fixture and test vehicle designs
- Shear force, thermal profiling, and electrical testing
BGA rework requires thorough planning, training and investment to meet the high reliability demands.
Frequently Asked Questions
Question 1: Can damaged BGA solder pads be repaired?
Yes, it is possible to repair damaged BGA pads using a variety of techniques including solder masking, copper tape inserts, or pad plating. Care must be taken to achieve the required flatness and precision for BGA mounting. Rework technicians have the skills to assess pad damage and execute repairs in many cases.
Question 2: How many times can a BGA component be reworked?
For standard eutectic and SAC alloy solder balls, BGAs components can typically be reworked 1-2 times reliably. The solder metallurgy undergoes structural changes during each process that degrade joint integrity after multiple cycles. For high-reliability applications, once removed BGAs are generally discarded and replaced.
Question 3: Can BGAs be reworked with a standard soldering iron?
It is extremely challenging to successfully remove and replace BGAs using only a soldering iron. The inability to heat all solder joints simultaneously risks damage. And inspection is limited without x-ray imaging. Basic rework stations with thermal control, optics, and imaging are considered the minimum tools for reliable BGA work.
Question 4: How are very small 01.00mm pitch BGAs reworked?
Ultra-fine pitch BGAs below 0.8mm demand advanced techniques like sequential multipoint flux printing and hot gas nozzles to control process variation. Microscopic optical alignment helps position components accurately. The process requires expert technicians with proper micro-rework tools.
Question 5: Can BGAs be removed and replaced by heating in an oven?
Baking boards in a standard solder reflow oven risks damage to other components on the board that may have lower temperature limits than BGA alloys require for reflow. The broad heating also can warp boards. Precision hot air tools localize heat only where needed.
Summary of BGA Rework
- BGA packages offer advantages but introduce rework challenges versus leaded components.
- Rework is required to remove faulty BGAs and replace components.
- BGA removal utilizes various heating methods to gently reflow all joints simultaneously.
- Site preparation and reballing prepare the new component for attachment.
- Precision alignment and controlled reflow solder the new BGA without damage.
- X-ray inspection validates hidden solder joint quality.
- Experienced technicians with specialized tools are mandatory for reliable rework.
- Services provide high quality BGA rework for companies without capabilities.
BGA rework and reballing allows repair of these sensitive components to avoid the high costs of remanufacturing complex and expensive PCB assemblies.
