BGA Assembly Services
JHY PCB began offering Ball Grid Array (BGA) Assembly services in 2011. We have very perfect BGA assembly process and advanced BGA assembly equipment. We can provide you with lower BGA assembly price and reduce the BGA assembly cost for you. Over time, we learned techniques and built experience with various types of BGA assembly jobs. Some of these included placing BGAs on both the top and bottom sides of the printed circuit board. We also developed the capability to place BGAs on both sides of the circuit board utilizing tin/lead as well as lead-free solders. Over these many year`s experience BGA assembly with X Ray inspection machine, right assembly procedure, we are very confident to say that we know, and we can build a high quality, good yield rate BGA assembly board. This is a challenging process, but at Yun Industrial, we do it without a problem.
In addition, we not only provide BGA assembly services, but also provide BGA PCB manufacture.
What is BGA Assembly?
A ball grid array (BGA) is a type of surface-mount packaging (a chip carrier) used for integrated circuits. Ball Grid Array packages are used to permanently mount devices such as microprocessors. A BGA can provide more interconnection pins than can be put on a dual in-line or flat package. The whole bottom surface of the device can be used, instead of just the perimeter. The leads are also on average shorter than with a perimeter-only type, leading to better performance at high speeds.
Soldering of BGA devices requires precise control and is usually done by automated processes. BGA devices are not suitable for socket mounting.
Ball grid array packaging is a method for reducing package size and integrating a greater number of functions on a single chip module. BGA (Ball Grid Array) also replaces solder balls on the component underside for SMT mounting. Our assembly capabilities include BGA assembly and rework up to 65mm squared up to 36 layer printed circuit board.
BGA Assembly Capability
Being one of the most well-known BGA assembly services, we are often referred to clients who are looking for experienced partners to materialize their complex designs. The following capabilities have helped us serve such clients efficiently:
Types of Leadless BGAs: We provide assembly for a wide range of leadless parts. We can handle the following types of BGAs and more:
Micro Ball Grid Array (µBGA)
Thin Chip Array Ball Grid Array (CTBGA)
Chip Array Ball Grid Array (CABGA)
Very Thin Chip Array Ball Grid Array (CVBGA)
Very Fine Pitch Ball Grid Array (VFBGA)
Land Grid Array (LGA)
Chip scale Package (CSP)
Wafer level chip scale packaging (WLCSP)
Testing and Inspection: We provide X-ray inspection for several chip packages mentioned above. In addition to this, we provide functional testing and Automated Optical Inspection (AOI) services.
Passive Footprints: The chip packages are provided in passive footprints such as 0201, 01005, POP, Pressfit, 0603, and 0402.
Sizes: The BGA assemblies are available in sizes ranging from 2mm x 3mm/1x1mm to 45mm/50x50mm.
Pitch Sizes: We provide BGA assemblies in minimum pitch sizes 0.4mm and placement accuracy +/- 0.03 mm.
BGA Assembly Services Features
BGA Assembly and Rework: We can rework on circuit boards up to 36 layers with 65mm squares.
The following features will help you understand the BGA assembly process at Sierra Assembly:
The process starts with the development of thermal profile by our experts as it is one of the most important processes in BGA assembly. We review the BGA datasheet and the PCB files provided by you to create a suitable thermal profile for your BGA assembly.
We always keep voids under 25% of the solder ball diameter. This is in adherence to IPC Class II or Class III quality guidelines.
Specialized thermal profiles are designed for leaded or lead-free BGAs to prevent higher temperatures or avoid open ball problems.
We conduct a detailed Design for Manufacturability (DFM) review to ensure the appropriateness. This includes checking maximum warpage, surface finishes, solder mask clearances, and more.
BGA Assemblies Beneficial Features
We provide BGA soldering, reballing, and BGA rework services at competitive prices.
Over the years, BGA packages have gained immense popularity owing to the following advantages:
Reduced Package Sizes: With miniaturization becoming a key trend, BGAs have allowed PCB assembly services like us to fulfill customer demands for miniature devices. These packages allow us to integrate various functions on a chip module by providing several interconnection pins. Leads follow shorter paths, which helps ensure excellent performance at high speeds.
Better Thermal Profiles: BGA packages have better thermal profiles than other packages because they have low thermal resistance. This helps the heat produced by integrated circuits to dissipate easily, thereby preventing the chips to heating.
6 Key Points of SMT Assembly Process for BGA Components
Superior Electrical Performance: These packages have shorter leads, which means they have low lead inductances. This low lead inductance ensures excellent electrical performance in high speed circuit boards. Inductance is the property that generates unwanted signal distortion in high-speed electronics applications.
Although some components with BGA packages are not so sensitive to humidity, all the components are advised to go through baking at a temperature of 125°C because no negative impact has been witnessed on low-temperature baking. That also works for bare PCBs (printed circuit boards) that are ready to go through SMT assembly. After all, moisture can be first eliminated with soldering balls defects going down and solderability improving.
In accordance with my assembly experience, solder paste printing is generally easy to be implemented on BGA components with a pitch of more than 0.8mm and QFP components with a pitch of 0.5mm. Sometimes, however, an issue might be encountered that tin needs to be compensated through manual operation since some solder balls haven't received sufficient solder paste printing, which leads soldering to be displaced or short circuits to occur.
Nevertheless, I don't think solder paste is more easily printed on BGA components with a pitch of 0.8mm than on QFP components with a pitch of 0.5mm. I believe that lots of engineers have been aware of the difference between horizontal printing and vertical printing on QFP with a pitch of 0.5mm, which can be explained from the perspective of mechanics. Thus, some printers are capable of providing 45° printing function. Based on the opinion that printing plays an essential role in SMT assembly, sufficient attention is suggested to being paid.
Based on practical assembly experience, because physical characteristics lead BGA components to feature high manufacturability, they are more easily to be mounted than QFP components with a pitch of 0.5mm. However, the main problem we have to face up with during SMT assembly process is that vibration usually occurs on components when large-scale nozzle with rubber ring is used to get components placed on circuit board with a size of more than 30mm. Based on analysis, it can be believed that it takes place as a result of too high pressure within nozzle due to excessive mounting strength and it can be eliminated after agreeable modifications.
Reflow soldering with hot air is a non-intuitive process during SMT assembly process or it can be defined as a special technology. Although BGA components share equivalent time and temperature curve of soldering with standard curve, it differs from majority of traditional SMDs in terms of reflow soldering. Solder joints of BGA components are under components, between component body and PCB, which determines that BGA components are much more affected on solder joints than traditional SMDs since pins of the latter are placed at periphery of component body. At least, they are directly exposed in hot air. Thermal resistance calculation and practices indicate that solder balls in central area of BGA component body suffer from thermal postponing, slow temperature rising and a low maximum temperature.
BGA SMT is closely associated with solder paste, components, PCB, silkscreen and soldering among which soldering items are the most difficult to be dealt with in reflow soldering process.
Fishbone diagram indicating concerning elements in the manufacturing process of PCB board containing BGA components is shown below.
The key element affecting reflow soldering lies in temperature curve setting. The specific method is to open a hole at the position of some pad at the center of BGA that is at the back side of PCB and then lead thermocouple probe through the hole from the bottom of PCB board with it stuck to backside of pad and fixed with high temperature tape. Next, reflow soldering temperature curve tester with parameters well set is placed into reflow soldering oven together with tray and probe. After times of comparison and analysis, an optimal temperature curve will be obtained.
Reflow temperature curve consists of four phases: preheating phase, heat preservation phase, reflow phase and cooling phase. Heating process and temperature curve should make package reach reflow temperature and then fall back to that of pad after solder balls are melted with intermetallic compound generated with pad. Inconsistent heating will lead packages to unevenly fall or incline towards one side or corner of reflow soldering, causing non-coplanarity and inadequate soldering.
The following two aspects should be emphasized as well in terms of BGA soldering:
Plastic packaging usually absorbs humidity. If a chip is instantly heated after absorbing humidity in the air, moisture diffusion will lead to cavities inside chip. As a result, general baking condition of plastic packages is under 100°C for 6 to 8 hours.
Prior to their applications, BGA components should be inspected to ensure their pins are clean and go through none oxidation.
Due to physical structures of BGA components, visual inspection fails to meet inspection demands of hidden solder joints of BGA components so X-ray inspection is called for to make soldering defects such as voids, short circuits, missing soldering balls, air holes etc. The only disadvantage of X-ray inspection is its high cost.
Along with a wide range of applications of BGA components, plus the popularity of electronics products for personal telecommunications, BGA rework has become increasingly significant. However, compared with QFP components, BGA components can never be used again once they are disassembled from circuit board.
Now that BGA packaging technology has become a mainstream in SMT assembly, its technology difficulty level can never be neglected and key points mentioned in this article should be carefully and correctly analyzed with issues rationally solved. When selecting a electronic contract manufacturer or assembler, professional manufacturing line should be picked up together with full-scale assembly capabilities and assembly equipment.
BGA Inspection Method
a. BGA Defects and Inspection Method
After soldering, BGA components possibly suffer from different defects due to components, assembly equipment, environment and soldering technologies. Leading BGA defects include misalignment, loose soldering, open circuits, cold soldering, bridging, short circuits and cavities. Furthermore, BGA solder balls possibly feature some issues as well such as missing or falling and uneven sizes. When it comes to BGA inspection, it's definitely difficult to judge soldering quality after soldering because solder balls are below chips. Traditional visual inspection fails to determine whether defects or cavities are available inside soldering joints. Professional inspection equipment has to be used to clearly judge the quality of solder joints.
After BGA components are leveraged in SMT assembly, inspection methods that are usually relied on include electrical test, boundary scan and X-ray inspection. Traditional electrical test is capable of scanning open circuit and short circuit defects. Boundary scanning technology, depending on inspection ports designed based on boundary scanning, provides an access to each solder joint on boundary connectors so that open circuits and short circuits can be inspected on components. Although boundary scan is capable of inspecting a wider range of invisible solder joints than electrical test, both methods only test electrical performance without reaching soldering quality inspection. To guarantee and improve the quality of manufacturing process, other methods have to be relied on for soldering quality inspection, especially those invisible solder joints. AXI (Automated X-ray Inspection) can effectively solve the issue and real-time monitoring can be carried out as well to ensure quality and real-time feedback for process control.
b. Optimal BGA Soldering Joint Standard
Optimal BGA soldering joints should be smooth, clear in boundary and void free and diameter, volume, grayscale and contrast should maintain the same among all the soldering joints with full alignment and no soldering balls generated. Compared with standards for optimal BGA soldering joints, qualified BGA solder joints feature lower requirement.
Misalignment. X-ray inspection device is capable of clearly indicating whether BGA solder balls are accurately compatible with pad positions on PCB board. Less than 25% displacement can be allowed.
Loose Soldering Joints. No loose soldering joints are allowed for BGA soldering.
Open Circuits and Cold Soldering Joints. When solder doesn't contact with corresponding pad or solder features bad flowing, open circuits and cold soldering joints will possibly take place. Open circuits and cold soldering joints aren't allowed for BGA soldering.
Bridging and Short Circuits. When solder is excessive or unsuitably placed, bridging and short circuits will possibly take place. As for BGA soldering joints, bridging and short circuits aren't allowed.
Cavity. The issue concerning cavity is a little complicated. X-ray inspection device is capable of demonstrating cavities on BGA components assembly.
The following tips are available as judgment standards:
1). Causes for Cavity Generation
2). Optimal Standard for Cavities
Cavities are available prior to soldering on BGA soldering balls, which possibly derive from solder ball manufacturing or solder paste constituent.
If through holes are designed to be under pad, external air will enter melting soldering balls through holes with cavities formed after cooling.
Pad features bad coating or pad is contaminant on surface.
Reflow soldering temperature curve is unsuitably set.
The air in cavities will possibly generate stress effect of shrinkage and expansion. The place where cavities take place will be stress focus, which is possibly the essential reason for stress cracks. BGA soldering joints with cavities will possibly lead to technical issues such as failure. According to standard regulated by IPC on BGA soldering joints, cavities on pad should not be 10% larger than solder ball area, that is, diameter of cavities should not be larger than 30% of solder ball diameter.
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