Package on Package (PoP) is an integrated circuit packaging technique to allow vertically combining discrete logic and memory ball grid array (BGA) packages. Two or more packages are installed on top of one another, i.e. stacked, with a standard interface to route signals between them. This allows higher density, for example in the mobile telephone / PDA market.
Contents[hide] 1Typical configurations2Benefits3JEDEC standardization4Other names5External links |
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解比
[edit]Typical configurations
There are two widely ud configurations for PoP:
Pure memory stacking (two or more memory only packages are stacked on top of each other)Logic (CPU) package in the bottom, memory package on top. For example, the bottom could be an application processor for a cell phone. The logic package goes on the bottom becau it requires many more BGA connections to the motherboard.
感动的事情Benefits
The most obvious benefit is motherboard space savings. PoP shares this trait with stacked-die packages. However there are veral key differences between stacked-die and stacked-package products.
The main financial benefit of package on package is that the memory device is decoupled from the logic device. Thus:
女性艺术摄影The memory package can be tested parately from the logic packageOnly "known good
" packages are ud in final asmbly (if the memory is bad only the memory is thrown away and so on). Compare this to stacked-die packages where the entire t is thrown away if either the memory or logic is bad.The end ur (for example cell phone maker or digital camera maker) controls the logistics. This means memory from different suppliers can be ud at different times without changing the logic. The memory becomes a commodity to be sourced from the lowest priced supplier. This particular point is also a benefit compared to PiP (package in package) which requires a specific memory device to be designed in and sourced upstream of the end ur.Becau the construction is like Lego, any mechanically mating top package can be ud. For a low-end phone, a smaller memory configuration may be ud on the top package. For a high-end phone, more memory could be ud with the same bottom package. This simplifies inventory control by the OEM. For a stacked-die package or even PiP (package in package), the exact memory configuration needs to be known weeks (or months) in advance.Becau the memory only comes into the mix at final asmbly, there is no reason for logic suppliers to source any memory. With a stacked-die device, the logic provider would need to buy wafers of memory from a memory supplier.
Electrically, PoP offers benefits by minimizing track length between, for example, a controller and a memory. This results in better electrical performance of the devices, since the shorter routing of interconnections between circuits results in faster signal propagation and reduction in noi and cross-talk.
公司要做Omap4的第三方软件合作商，看了下pandaboard的结构与布局，发现这个POP memory 与CPU 堆叠在一起。这样整起来对于传统的焊接工艺是个很大的挑战！
有一句比较有意思的话：It has been suggested that this article or ction be merged with System in package. （意思是说POP封装某种意义上应该是SIP系统级封装的一种形式），关于SIP的文章文章比较多，大家用System in package为关键词在百度或老毛桃怎么用谷歌里面就能搜索到很多文章。摘抄上述网址的部分内容参考：漂亮的女生>美好的瞬间
Typical configurations
There are two widely ud configurations for PoP:
1、 Pure memory stacking (two or more memory only packages are stacked on top of each other)
2、 Logic package in the bottom, memory package on top. For example, the bottom could be an application processor for a cell phone. The logic package goes on the bottom becau it requires many more BGA connections to the motherboard.
谈回到这个具体的案例，通过与国基工程师的交流，他们也是在评估此工艺，以前也没有接触过POP底填工艺。在去之前我们给他们推荐了韩国元化学WON的WE-1007NBLA，但是也没有在POP上成功实施的经验。他们目前经过评估暂定了Loctite公司的3536型号，据说是在POP上有成功的应用。其实3536之前我就有接触过，请参看此篇文章《LOCTITE 3536 UNDERFILL》。而之前接触的此材料实际上就是直接应用在二道condary underfill里面的。据此而知POP上的underfill与传统的condary underfill差异应该不大。但有两点需要注意的地方，首先其粘度不能太大，类似乐泰3515和韩国元化学的WE-1007NBLA的粘度都在4000cps左右， 两层同时填充的话估计有一定的难度。而类似乐泰UF3800及道尔DU986系列的粘度在200至400cps，由于流动性太强，估计难以上下两层都进行均匀填充。而目前的3536粘度大约为2000cps左右，介于两者之间，应该是比较适合POP底部填充的。这是当时在上海与客户直接交流的初步结论，但对于POP封装与传统BGA对underfill胶水有什么更多不同其实也不是太了解。其实如果据此简单推论的话，那么韩国元
化学的WE-3008应该也能适用于POP的封装，因为其粘度也大约在2000cps左右，后来咨询了一下韩国元化学的金社长，果然他们的WE-3008在三星手机上面就有用于POP底部填充的。
其实后来思考了一下，其实粘度不应该是简单决定是否适合POP封装的必要条件，因为后面在电子胶水论坛网友讨论zymet公司的underfill时，其中有一段是这样写的“Zymet公司日前推出新的可维修的底部填充胶CN-1728，这一产品是专为POP工艺的组装而设计的。POP的底部填充胶工艺与BGA的工艺有相当大的不同，与以前的同类产品相比，CN-1728有更低的热澎涨系数和较高的玻璃转换温度(Tg)，与助焊剂有更好的兼容性，这些都使其具有卓越的热循环性能表现。 CN-1728是具有快速流动的竹荪蛋的做法毛细管效应底部填充胶，其黏度为900 cps,可以在150 °C的温度下一分钟完成固化。这种特性使得CN-1728可以适应生产线上的高速大批量生产。 维修可以通过提高温度到170°C -180°C后，移除PoP周围的胶材。然后加热至焊锡熔融温度后移除BGA，再回到170°C -180°C，并轻易的去除剩余的胶材”，后来在网上找到了CN1728的TDS资料，其粘度只有900cps。所以当时在上海的结论也未必是正确的。
不过最终可以确认的一点是POP用的underfill与传统BGA下使用的underfill差异应该不是特
别大，而且也远没有上升到一道underfill的要求（例如对填料里面的射线要求等），毕竟POP 也是将封装好的IC进行叠加，而不是直接用裸芯片进行叠加，底填材料不直接接触硅晶片，当然也不需要一道underfill那么高的要求了。另外关于POP封装的返修应该要比BGA返修更麻烦一些， 在网上找到了一份OKI返修台针对POP封装的返修指南，大家可以参考一下！北京万圣节活动
