Packaging technology is actually a technology of packaging integrated circuits. Take our common memory for example, what we actually see is not the size and appearance of the real memory, but the product after the memory chip is packaged. This kind of packaging is necessary and crucial for the chip. Because the chip must be isolated from the outside world, to prevent impurities in the air from corroding the chip circuit, resulting in the decline of electrical performance. On the other hand, the packaged chip is also more convenient to install and transport. Because the quality of packaging technology also directly affects the performance of the chip and the design and manufacture of the PCB (printed circuit board) connected to it, it is very important.
At present, although there are various packaging technologies widely used in the industry, 90% of them adopt TSOP (as shown in figure 1), which is called Thin Small Outline Package in English, and it is the representative of the second generation memory packaging technology that appeared in the 1980s. A typical feature of TSOP is to manufacture pins around the packaged chip. For example, SDRAM's IC has pins on both sides, and SGRAM's IC has pins on all sides. TSOP is suitable for mounting wiring on PCB with SMT surface mounting technology, with reduced package size and parasitic parameters, suitable for high-frequency applications, convenient operation and high reliability. Brands that adopt this technology include Samsung, Hyundai and Kingston. At present, TSOP is widely used in the manufacture of SDRAM memory, but with the passage of time and the progress of technology, TSOP is increasingly unsuitable for the new generation of high-frequency and high-speed memory.
Like microprocessors, the technology of memory chips is constantly updated. You may have found that the particles on the memory stick in your hand are gradually changing, becoming smaller and more delicate than before. The changes are not only superficial, but these new chips have made great progress compared with their predecessors in terms of applicable frequency and electrical characteristics. This crystallization should be attributed to the choice of new memory chip packaging technology by those manufacturers. The new chip packaging technology represented by TinyBGA and BLP technology has gradually matured.
First of all, I would like to mention TinyBGA technology, which is a patent of Kingmax. 1998 was successfully developed in August. To understand TinyBGA technology, we must first know what BGA is. BGA is the abbreviation of Ball-grid-Array, namely ball grid array package, which is a new generation of chip packaging technology. I/O terminals are distributed under the package in the form of circular or columnar solder joints. The advantage of BGA technology is that it can increase the number and spacing of I/O and eliminate the production cost and reliability problems caused by high I/O number. It has been widely used in the packaging field of large-scale integrated circuits such as notebook computer memory and motherboard chipset. For example, the well-known Intel 845PE and VIA KT400 chipsets are all products adopting this packaging technology.
TinyBGA means miniature BGA. TinyBGA is called Tiny Ball Grid Array in English, and the ratio of chip area to package area is not less than 1: 1. 14, which belongs to a branch of BGA packaging technology. The application of this innovative technology can increase the storage capacity of DRAM in all computers by 2 to 3 times without changing the volume. TinyBGA adopts BT resin instead of traditional TSOP process, which has smaller volume and better heat dissipation and electrical performance.
TinyBGA packaging technology greatly improves the storage capacity per square inch, and 256M memory can be manufactured on a PCB with the same space as 128M TSOP packaged 144-pin SO-DIMM. For two memory chips of the same size, the capacity of TinyBGA packaging method is twice that of TSOP, but the price has not changed significantly. The data shows that the memory products with TinyBGA packaging technology are only one third of TSOP packaging compared with the same capacity. When the process diameter of the memory module is less than 0.25 m, the cost of TinyBGA package is less than TSOP package.
I/O end of TinyBGA package memory is led out from the center of the chip, and TSOP is led out from the periphery. This effectively shortens the signal transmission distance, and the length of the signal transmission line is only a quarter of that of the traditional TSOP technology, so the signal attenuation is also reduced accordingly. This not only greatly improves the anti-interference and anti-noise performance of the chip, but also improves the electrical performance. TinyBGA package chip can resist the extra of up to 300MHz, while traditional TSOP package can only resist the extra of 150MHz. Moreover, the memory packaged with TinyBGA is not only smaller than TSOP chip with the same capacity, but also thinner (the packaging height is less than 0.8mm), and the effective heat dissipation path from the metal substrate to the radiator is only 0.36 mm, so TinyBGA memory has higher heat conduction efficiency, which is very suitable for long-term running systems and has excellent stability. Repeated tests show that the thermal impedance of TinyBGA is 75% lower than that of TSOP. Obviously, compared with the traditional TSOP packaging method, TinyBGA packaging method has a faster and more effective heat dissipation method.
In addition to TinyBGA, BLP technology is also a common technology in the market at present. The full English name of BLP is Bottom Led Plastic, and the ratio of chip area to package area is greater than 1: 1. 1, which conforms to CSP (chip scale package) potting specification. Not only the height and area are small, but also the electrical characteristics are further improved and the manufacturing cost is not high. Widely used in the manufacture of SDRAM\RDRAM\DDR and other new generation memories. As the price of plastic packaging substrate, the key component of BLP packaging, continues to drop, BLP packaging memory will soon enter the homes of ordinary users.
The packaging method of memory particles has experienced the changes of DIP, SIP, SOJ, TSOP, BGA and CSP, which can be described as ups and downs. Before introducing memory granule encapsulation, let's take a look at three modules of memory.
In the early PC, the memory stick was directly welded to the motherboard, so the capacity of RAM was fixed and it was very troublesome to expand. In order to expand the capacity of RAM, the designer later made the memory stick into a special memory stick and added it when necessary.
Single in-line memory module
Small size, light weight, inserted in the special slot of the motherboard. There is a foolproof design on the slot, which can avoid being inserted backwards. There are metal clips at both ends of the slot, which is the prototype of today's memory. Its advantage lies in the standard pin design, which is compatible with almost all PCs.
Dual in-line memory module
Similar to SIMM, but slightly larger. The difference is that some pins of SIMM are connected back and forth, while each pin of DIMM is separated, so the electrical performance has been greatly improved, which can accommodate more pins without making the module very large, so it is easy to get a larger capacity RAM.
RIMM(Rambus embedded memory module)
It looks a bit like a DIMM, but it is bigger and has better performance, but it is expensive and has higher calorific value. In order to solve the heating problem, each module has a long heat sink.