How to Reball and Test BGA Chip
Thursday, April 05, 2007
By this time, every memory module manufacturer should have a whole drawer full of pulled DDR2 chips and do not know what to do with them. For the past year, module manufacturers have been pulling chips out of non-working modules and replaced them with new memory chips to make the module work. Yet, they have no way to confirm that the pulled chip is really bad or just a bad solder joint. To do that verification, they would have to reball the BGA chip, test it and then reuse it on a new module. To most memory module manufacturers, reball is a new process to them. They neither have the equipment nor the know how to do it. Yet, they do have to seriously think about that when the accumulation has gone beyond control.
BGA芯片如何重新植球和测试
目前每个内存条制造商都有成抽屉的拔下来的DDR2芯片，不知如何处理。过去的一年里，内存条制造商从不能用的内存条取下坏芯片换上好的来修复内存条。目前他们还无法确定是取下来的芯片坏了还是虚焊。为了验证芯片好坏，他们不得不做芯片重新植球、测试并把芯片重新投入使用。对于大部分制造商重新植球是新鲜事，他们既没有设备也不知道如何去做。当取下的芯片堆积失去控制的时候，他们的确在认真考虑这个问题。
The Professional Reball Process
The proper reball process is listed in the flow chart:
专业重新植球加工过程
流程图列出恰当的重新植球加工过程
作者: 张先生 时间: 2007-5-16 07:25 标题: 显微检查 Visual Inspection
Visual Inspection is normally done under a magnifying scope. The operator should be looking for hairline solder bridges, hairline cracks, and also burnt marks. All those are indicators of damage chips that would be a waste of time on repair.
目测检查
目测检查一般在显微镜下实施。操作人员寻找极细的焊桥、裂缝及烧痕。所有这些都提示为损坏的芯片，修理他们是浪费时间。
作者: 张先生 时间: 2007-5-16 07:26 标题: 清除植球 Ball removal
The old balls must first be removed. Soldering iron and solder wick is the best method. Flux are added to help the melting temperature and the easy flow and easy pick-up of the old solder residues. Sometimes hot air supply with the proper size nostril would also help.
清除植球
旧的球必须被先清除掉。用烙铁加吸锡带是最好的方法。加助焊剂的好处是降低熔点、增加流动性以及容易去除焊锡残留物。用适当大小的出气孔加热空气也对处理过程有益。
作者: 张先生 时间: 2007-5-16 07:26 标题: 烘干与测试 Once it is cleaned, the chip should be baked to dry. This is to eliminate the bubbling effect that might happen on the substrate. The baking process should be 24 hours under 70 degree C.
一旦清除完毕，芯片需要烘干以便消除可能发生在底层上的气泡效应。烘干过程为摄氏70度24小时。
Test without balls
At this point, the chips should be functionally tested to take out the electrically bad chips. Since these are pulled chips, multi-test pattern test should be applied to weed out the hidden bad cells and non-functionalities. Since the balls have been removed at this point, the test socket should be of pogo-pin type to ensure contact on a flat surface (no ball). Only the good chips are put forth for the physical reball process
测试无球芯片
至此，应该对芯片进行功能测试以便剔除电气损坏的芯片。因为是拔下来的芯片，所以要用多种模式测试，以便发现隐藏的坏单元和功能失效。又因为锡球已经去除，测试座应该是簧片型的，便于接触平坦的触点。当选出好的芯片时就可以投入重新植球的加工过程。
作者: 张先生 时间: 2007-5-16 07:35 标题: 刷粘性助焊剂 The Physical Reball Process
The reball process consist of 3 procedures: the solder paste screening, the placement of balls and the temperature reflow.
First, a thin layer of fresh solder paste is screened onto the ball pads. This solder paste acts as an adhesive agent for the ball and also supply extra flux to the joint. A cavity fixture must be used to hold the chip and the stencil for proper screening. Multi-chip fixture that can screen a dozen chips at the same time is used to speed up the operations.
作者: 张先生 时间: 2007-5-16 07:36 标题: 植球过程 The next step is to screen the ball spheres onto the chip. A vacuum ball pickup/deposit fixture is used to pickup the spheres from the tray and release them onto the chip. The balls should sit properly and are loosely adhered to the pads after this process.
下一步是用钢网把球放到芯片上。用一个真空拾球/存储器从盘子里拾球并放到芯片上。处理完成后锡球的放置要合适，松松的粘在触点上。
作者: 张先生 时间: 2007-5-16 07:36 标题: 回流焊 Next is the reflow process. The reflow process relies on the temperature profile setting. The temperature setting also depends on the construction of the spheres (ball), whether they are leaded or no lead.
接着是回流焊。回流过程依赖于温度曲线的设定。温度的设定还依赖于锡球的构造，不管有铅还是无铅。
作者: 张先生 时间: 2007-5-16 07:36 标题: 芯片分选测试和封装 Final Test and Package
Once the balls are paked onto the chips, final electrical test would be applied. This is generally done with functional DRAM tester with tuning fork type of socket. The tuning fork contact is a U shape forceps designed to grab hold of the solder ball for electrical contacts. Since different manufacturer have different chip package dimensions, different size inserts have to available to test the different package sizes
最终测试与封装
一旦植球完成，就要做电气测试。 一般用有音叉型座的DRAM功能测试仪完成。音叉触面是一个U型簧片，用来抓住锡球作电气接触。因为不同的制造厂商的芯片封装大小不同，必须有不同尺寸的插座来测试封装不同大小的芯片。
作者: 张先生 时间: 2007-5-16 07:37
Since solder balls do oxidize quickly and builds an oxide coat that reduces the soldering characteristic of the ball, the chips should be vacuum sealed shortly after the reball process. The chips are usually put into trays and the entire tray is vacuum sealed into an anti-static bag. This completes the many steps of reballing the DDR2 memory chips.
因为很容易氧化并且形成一个氧化层覆盖会降低锡球的焊接特性，所以在重新植球加工后应尽快真空封装。芯片通常放在一个碟子里并真空封装在抗静电袋里。这就完成了DDR2内存芯片重新植球的整个过程。
Complexity of the Setup
An investment of tools is required in the DDR2 reball. Since DDR2 DRAM package comes in 20 different physical sizes, different fixture is required for each of the sizes. This includes the solder paste stencil, the cavity chip holder and the ball screening stencil. The ball pickup/deposit head would also need to be customized to each chip size for consistent performance.
起步的复杂性
要对DDR2重新植球需要对工具的投资。因为DDR2 DRAM有20种不同尺寸的物理封装，每种都需要不同大小的固定器。包括焊膏钢网、凹型夹持器以及求的漏网。球的捡拾/放置头也要适用于每种芯片的尺寸，以便保持连续使用的性能。
Since test is an important step to ensure the reball chips will work, electronic microscope is required for visual inspections. A set of chip tester with pogo pin BGA sockets will be required for testing chips that had the balls removed. A tuning fork socket tester is also needed to do final test without damaging the balls. Since the chips are in different sizes, full set of 20 some socket inserts (size limiter) are required.
因为测试是确定芯片能否工作的重要步骤，目测需要电子显微镜（实际上是放大后可在计算机上显示的设备）。一组弹簧针脚测试座用来测试无球的芯片。还有不会损坏植球的音叉测试座用来作最终测试。由于芯片的尺寸不同，全部20种左右插座都是用得着的。
There is also the skill labor required. I have heard of 30 minutes process for reballing each chip. Yet, with the proper equipment and fully trained labor, this task can be achieved in an average of 10 minutes.
还要有熟练工人。我听说每个重新植球的芯片需要30分钟完成。但是，有恰当的设备，非常熟练的工人，这一任务平均在10分钟完成。
Price Cost Ratio for Reball
Whether an in-house DDR2 BGA reball would pay is purely based on simple mathematics. The first thing is to look at equipment amortization. What does it take to gather all the equipments, space and the training? How many chips can an operator do in a day? You then divide the cost of equipment and labor to per chip cost. If that is still attractive, you will then be able to come out ahead.
重新植球的价格成本比
内部的DDR2 BGA重新植球无论怎样花费都是由简单的数学公式决定的。首先要看设备的装备情况。所有的设备、场地和人员训练加在一起是多少？一个操作工一天可以完成多少芯片？你把设备和劳动力成本用芯片成本来除。如果结果是有吸引力的，那你就去做这个生意。
On the other hand, there is also a time/price risk factor involved. As DRAM prices fluctuates daily, your DRAM might lose its value while in inventory getting reballed. Yesterday抯 256Mbit DRAM might no longer fetch the same amount as today抯 inventory or vise versa.
另一方面，还有时间/价格风险因数。DRAM价格天天在变，当你要去投资重新植球的时候，你的DRAM可能失去价值。昨天的256M位可能不如今天的了。投资或者放弃。
In House process vs Subcontract
When the labor and equipment investment cost is over the cost of subcontract repair, it is time to consider whether to do it in-house or just subcontract it out to some lower labor country. Use of off shore labor in this labor intensive process may allow substantial saving. It will avoid capital investment as well as long term maintenance and training.
However, you are also trading quick turnaround with a turn around of 1-2 weeks
内部加工还是转包合同
当劳动力和设备投资成本超过转包合同维修，这就是考虑内部加工还是转包到劳动力成本低的国家的时候了。在劳力密集型工作中使用离岸劳力可能有实质性的节省，可以避免资金投入、长期维持和训练。
然而，你还要保持1~2周周转一次的快速交易。
