-
- News
- Books
Featured Books
- smt007 Magazine
Latest Issues
Current IssueBox Build
One trend is to add box build and final assembly to your product offering. In this issue, we explore the opportunities and risks of adding system assembly to your service portfolio.
IPC APEX EXPO 2024 Pre-show
This month’s issue devotes its pages to a comprehensive preview of the IPC APEX EXPO 2024 event. Whether your role is technical or business, if you're new-to-the-industry or seasoned veteran, you'll find value throughout this program.
Boost Your Sales
Every part of your business can be evaluated as a process, including your sales funnel. Optimizing your selling process requires a coordinated effort between marketing and sales. In this issue, industry experts in marketing and sales offer their best advice on how to boost your sales efforts.
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - smt007 Magazine
Reballing Rework: The Bright New Future
December 31, 1969 |Estimated reading time: 5 minutes
By Kris Roberson, MIT, BEST Inc.
Components are always evolving. One of those evolutions brought our industry the BGA. Add in the advent of the RoHS and WEEE directives, and BGA rework becomes an exciting topic. To rework, e.g. remove and replace, a BGA, or in some cases to simply install a BGA on a lead-free assembly, one process stands out as necessary: reballing. Here, we look at the history and the why and how of reballing, specifically examining a reballing technique that could increase operator ease and assembly reliability.BGAs evolved to fill a need. Components were getting more complex yet smaller at the same time. Electronic assemblies also shrank, leaving smaller total board real estate in which to work. Lead pitch gradually reached the limit of solderability without bridging. Enter the area array packages. By moving leads to the bottom of the component, available space for connections was increased significantly (3050% increase) without increasing package size. Component designers quickly realized the potential of area array packages and moved to implement them in the electronics industry. In a perfect world, the area array package specifically the BGA would solve all the electronic industry's component real estate problems and would never need to be removed or replaced. Since we live in a less-than-perfect world, BGAs are removed and replaced with regularity.
Why Reball?When a BGA is removed, replaced, or in some cases before it is placed the first time, its solder balls must be replaced. Let's address the last case first. BGAs manufactured for a tin/lead assembly operation would have to be reballed if the component is to be used in a lead-free assembly. There is a flip side to that issue as well. Many component manufacturers are streamlining their operations and making all products lead-free. For electronic assemblers dealing with medical or military applications, lead-free components create a problem. In some cases, the customer may require a small amount of lead in the final assembly; for example, there are contracts from the U.S. Department of Defense (DOD) that state that a minimum of 1% lead must be present in the solder used for electronic component attachment. In these cases, a pure lead-free-balled BGA will need to be reballed with leaded solder balls before initial placement on the electronic assembly. The other reballing scenario remove and replace will require reballing of the device if the BGA is to be reused in an electronic assembly.
To understand the how of reballing, it is useful to understand what happens to the BGA connections when removing the BGA from the assembly. In this example, the removal process uses a stand-alone rework station incorporating a nozzle, hot gas reflow, and automated removal probe. To remove the BGA, there must be a time/temperature profile (TTP), the set of instructions used by the reflow oven or rework station that defines how long to heat the device at what temperature. The goal of the TTP is to melt the solder alloy particles within the solder paste or BGA ball without overheating or damaging the electrical components. Use the same TTP created to place the BGA onto the original assembly as a starting point to develop the correct TTP BGA removal.
As the assembly heats, the balls of the BGA will reach a point where the solder alloy will change to its liquid form. Above the liquidus state of the solder, the BGA package can be removed without damage to the BGA or the circuit board. Some of the solder balls will adhere to the circuit board, some will split between the circuit board and the device, and still others will adhere completely to the BGA's substrate. This is the first reason why the device must be reballed before attempting to place it on another assembly. BGA balls must be even across the surface of the BGA to ensure that the device is parallel to the circuit board in the final assembly. The removed device also must be reballed because the solder now has been heated multiple times, which causes material breakdown. The bonds formed with the "old" solder are not as strong and therefore not as reliable as newly formed solder connections.
The ProcessYou now have a device that is either removed from an assembly and has old, uneven solder balls, or a new device that has been manufactured with tin/lead solder balls, which cannot be used in a lead-free assembly (or vice versa). From this point, the how of reballing is the same.
First, the solder balls must be removed from the bottom of the BGA. This procedure is as simple as cleaning a circuit land in preparation for component placement. One method is to use a soldering iron with an appropriately sized tip, flux, and solder wick to remove the solder balls from the bottom surface of the BGA.
Next, the device must be cleaned. Use isopropyl alcohol, or another cleaning process as approved for the specific assembly operation, and a lint-free cloth to wipe off the BGA device pads (Figure 1).
To replace the solder balls, select an appropriately sized and configured single-use reballing platform. Single-use reballing platforms can be customized to any BGA size and ball configuration (Figure 2). Apply paste flux to the bottom of the BGA device and align the device to the single-use reballing platform preform.
Next, reflow the device using either a reflow oven, rework system or other heat source set to the appropriate temperature. Temperature and heat time parameters depend on the device. Check with the device or solder ball manufacturer for the proper TTP of the BGA device.
Figure 3. Polyimide tape is removed prior to cleaning the newly reflowed BGA.
When the device has completely cooled, peel the polyimide tape away from the device (Figure 3). Clean the BGA as before. The BGA device now is reballed and ready to be placed on an electronic assembly (Figure 4).
ConclusionThe BGA has come a long way in a short time. It has gone from the "new kid on the block" to a widely used solution to the ever-shrinking assembly. With the proper time/temperature profile and single-use reballing platform preforms, reballing of the BGA isn't a thing to be feared. BGA reballing now has a bright future.
Kris Roberson, MIT, senior technical instructor, BEST Inc., may be contacted at (847) 797-9250; kroberson@solder.net.