乡亲们
罗布前往瓜达拉哈拉解决QFNvoiding 问题......
As Rob sat on the airplane, he was excited to go to GDL (Guadalajara, Mexico) to help solve the voiding problem.He knew Patty would be a little peeved that he asked for Pete to come along, but she was gracious, recognizing that Rob would benefit from a success in this effort.
当飞机盘旋着准备降落时，罗布正在为有点滑稽的海关之旅做准备。他一直认为，用红灯/绿灯来判断是否要搜查行李的方法很不寻常。
从机场驱车约 40 公里，穿过 GDL 繁忙的交通到达工厂。罗布过去曾与米格尔共事过，对他这位工艺工程师非常尊敬。米格尔告诉他们，已经安排好与现场总经理，一位名叫格兰特-威尔逊（Grant Wilson）的美国同事举行启动会议。
会议开始后，罗布用西班牙语向威尔逊做了自我介绍。
"哇，"威尔逊笑着说，"当被问及我是双语、三语还是美国人时，我不得不说我是美国人。"不过，我正在上西班牙语课，"他接着说。
罗布看了米格尔一眼，见他翻了个白眼。但罗伯认为，威尔逊上西班牙语课至少是个不错的表示。
"罗布建议说："也许有人可以告诉我们已经采取了哪些行动，现状如何。
"米格尔，你能给罗布介绍一下我们现在的位置吗？"威尔逊问道。
Miguel began, “The warranty send back rate is 5% on Druid phones.Almost all of these failures have been traced to high powered QFNs that have significant voiding under the thermal pad.The voiding percentage is about 50-70%.About a week ago we obtained Derrick Herron, Dr Yan Liu and Dr Ning-Cheng Lee’s recent paper, Voiding Control at QFN Assembly, at SMTAI2011. We changed our stencil design, as suggested in the paper, to allow for venting of the solder paste volatiles and voiding went down to 30 to 50%.”
“What level of voiding would be acceptable?” Rob asked.
"我们不确定。"米格尔回答。
“So it seems we have two issues, one is to determine if 30 to 50% voiding is OK and the other is to see if we can reduce it further,” Grant Wilson reasonably commented.
“My sense is that we need to be in the less than 30% range,” Rob added. “This may require that we use solder preforms.Voiding is caused by outgassing but also by insufficient solder,” Rob finished.
"威尔逊命令道："好，你们两个去解决问题，然后给我三天时间。
Rob, Pete, and Miguel headed off to get started on their assignment.Rob was really glad Pete was there. He was an expert in setting up and optimizing the component placement machines that were at this site. Fortunately, Rob had also brought some solder preforms with him, expecting that they would be required.A call to the QFN vendor confirmed that less than 30% voiding should be the target.Rob looked at the data and x-ray images of the work that Miguel and his team did to reduce the voiding by improving the venting of the flux volatiles.He was impressed.But he didn’t think it would be enough.
(对话译自西班牙文）
“Miguel, I’m almost certain that we will need to use solder preforms on the two most critical QFNs,” Rob began.“There are two major reasons for voiding, the first is flux volatiles forming voids, the second is solder starvation.Most people don’t realize that solder paste is only 50% by volume metal.In cases like this, where we really need low voiding, often the only path to success is to use solder preforms to add solder metal,” he finished.
Rob then showed Miguel Seth Homer’s SMTAI 2011 paper Minimizing Voiding in QFN Packages Using Solder Preforms.This paper describes the process steps needed to achieve a successful QFN solder preform process.Rob and Miguel spent the better part of a day setting up one assembly line to assemble with the solder preforms using this paper as a guide.They assembled 100 phones and the voiding level was 10.5%.
第二天一大早，他们就见到了格兰特-威尔逊。
"从你们俩脸上的笑容来看，我猜你们都成功了？"威尔逊问道。
Rob went on to explain how they determined that solder preforms were needed.He explained the process and waited for questions.
“What do solder preforms cost?” Grant asked.
"罗布回答说："它们的数量约为 0.02 美元（美国），但要知道，现在每 200 美元手机的保修成本至少为 10 美元（0.05×200）。
"威尔逊问道："你必须放慢处理速度吗？威尔逊问道。"我一直很喜欢你和帕蒂-科尔曼为教授所做的工作，你们让我相信了吞吐量的重要性。
“The Professor has pointed out that almost never is a line completely balanced.Your flexible placers were waiting four seconds for the chip shooters.We put the preforms on the flexible placer and tuned up both machines by optimizing the feeder placement. The cycle time is now 1.25 seconds faster for the 3 phone per PCB card,” Rob answered.
"我很好奇，最大的挑战是什么？"格兰特问道。
“Rob pointed out that the correct placement of the preform on the solder paste deposit for the heat sink part of the QFN is critical.We needed to assure that the preform was pushed into the paste far enough to leave a ring of paste around the preform to assure good mating with the QFN. We couldn't have done this without Pete, he really knows the placement machines,” Miguel answered.
米格尔随后向威尔逊展示了塞斯-霍默论文中的一幅图片，展示了这种情况。
“Guys thanks for the great work.I have to admit that I didn’t really know anything about solder preforms, before today.In certain cases it is obvious that they can be lifesavers!” Grant summed up the situation.
"为了庆祝你的成功，今晚我请客，地点是圣土狼餐厅，我们 7 点在那里见。"威尔逊提议道。
"谢谢，"罗布、皮特和米格尔异口同声地说。
Santo Coyote 是罗布在瓜达拉哈拉最喜欢的餐厅，但也是帕蒂最喜欢的餐厅。
后记：三个月后，保修退回率接近零。米格尔因为参与解决了这个代价高昂的问题而被提升为高级工程师。
干杯
罗恩博士
