BGA, CGA AND
Repair and Rework
At a time like this, where electronics are more and more complex, the grid array devices such as CGA and BGA are becoming increasingly widespread and important.
They often are very strategic and expensive components and they control valuable boards.
In the last few years BGA is rapidly becoming the industry standard for high lead-count microelectronics packaging also in very conservative fields such as aerospace.
They are surface mounted devices (SMD) that have to be solely machine mounted since it’s impossible to perform any manual soldering. They don’t have gull-wing leads such as a Plastic Quad Flat Package (PQFP) in fact, but they have some spheres (balls) or columns connected under the component case that provide the solder connection to the board after the thermal cycle of soldering.
Also among the connectors the needs are consequently increased: next-generation processors need next-generation connectivity to keep pace with the growing demand for bandwidth even as space, weight, and power savings become critical.
Those connectors are commonly referred to as HIGH DENSITY or VITA.
The assembly process is similar to the other grid array devices, in fact they have all the connections underneath the connector case and their terminations are commonly named “solder charged” or “ball equipped” and those either need some special care.
Different for shape and requirements
In order to mount these components therefore some special care it’s required. Three are their defining features:
The reflow process and therefore the forming of the solder joints happen completely under the component case, in a concealed area and the joints also carry the component’s weight. The assembly can be done only using an automatic soldering machinery since the joints cannot be reached by manual soldering;
The joints cannot be inspected with usual vision tools such as AOI (automatic optical inspection) or microscopes. You must have an X-ray machine and a side view video microscope in order to perform all the necessary controls incoming, inprocess and final;
in case of issues, the solder joints cannot be singly reworked since they cannot be reached with a soldering iron. In order to correct them you have to face a thermal cycle or a removal and in the latter case the balls or the columns get lost and you have to replace the component or, restore it through a special process known as REBALLING.
That’s why we like them
Surely they need some special care but they’re worth it. Their particular shape allows an incredible quantity of connections compared to a quad flat package and they provide unparalleled performances. Some BGA have up to 2000 lead in spheres of 0.2mm diameter spaced less than 1mm. HD connectors can have more than 500 pins further expandable and arranged in various arrays. It’s easy to understand how this standard meets the needs for data-intensive processing, for example in the aerospace industries, where both ruggedness and high-speed performance are crucial.
We understand their value and we treat them with passion and care everyday.
What’s the process’approach
In order to get good solder results first of all it’s necessary to characterize the process, planning all the activities and paying special attention to some key features such as: the alloys involved, the starting condition of the components, the PCB landing status e.c.
The process should be planned carefully: a FPC (Factory Production Control) plan must rule all the steps and a special care should be paid to all the set ups and toolings that can affect the solder paste screen printing or the component placement since the small size of the balls leave very small room for mistakes.
Also the reflow profile should be validated using a spare piece if possible. Sometimes when that’s not possible then skill and experience become vital along with consolidated procedures for every component shape and footprint in order to minimize varying process conditions and strike the correct profile in one go.
The importance of inspections
In order to maintain a good control over the process the inspections are a huge part of the strategy.
Since the area of interest is in this case, invisible to the naked eye and also to the common visual tools, special equipment is needed.
The components should be checked first of all during incoming controls. In this phase a microscope can do the job, the better if it has great magnification and good measuring tools such as our digital microscope KEYENCE VHX-7000.
In the process an X-ray machine is imperative instead. It serves to check the correct placement and alignment during setups and during production sampling and at the end it’s necessary in order to verify that the reflow has been successfully completed.
In order to pull the correct information from an X-ray analysis a good machinery is needed to obtain good images but the skill and training of the operator can make the difference in their evaluation. With the right knowledge the greyscale can give much information besides the simple remark of voids and short circuiting. It can tell a lot in fact about the quality of the reflow process, the thickness of the intermetallic compound and the general reliability of the connections.
The importance of visual checks
After years of experience we noted that sometimes a visual inspection can be complementary to the X-ray inspection for some sort of issues such as “head in pillow” defect. For this peculiar kind of inspection related with the connection with the PCB landings we use a digital video microscope with side lenses specially designed for BGA inspection that allows us to appreciate some features not immediately noticeable during an X-ray inspection.
The synergy between technical skills, appropriate tools and machinery paired to a great passion and commitment it’s the key for an assembly service whose aim is customer satisfaction.