[introduction]As electronic equipment more and more advanced, integrated circuit encloses dimension to also become smaller and smaller, but this is to increase the density that cite a base not just. The higher density that cite a base is very important to having a lot of interrelating advanced systems, but in more advanced network parts of an apparatus, still having a main reason is to should be what move in these systems to interrelate limitation of bandwidth of set of parts of an apparatus. 224G system and IP are transferring from the concept commercial product, this means the bandwidth that encloses a design to need to satisfy these systems to ask.

As electronic equipment more and more advanced, integrated circuit encloses dimension to also become smaller and smaller, but this is to increase the density that cite a base not just. The higher density that cite a base is very important to having a lot of interrelating advanced systems, but in more advanced network parts of an apparatus, still having a main reason is to should be what move in these systems to interrelate limitation of bandwidth of set of parts of an apparatus. 224G system and IP are transferring from the concept commercial product, this means the bandwidth that encloses a design to need to satisfy these systems to ask.

In enclosing ” tall bandwidth ” not be a new idea, and enclose design personnel to know how compose builds what can leave the job in extremely high frequency rate to interrelate. For example, in MMIC, interface can with offerring high frequency rate relative to higher power, although be enclosed without high density,also can accomplish this. These enclosing is not burgeoning thing, they had used a few years in certain example.

224G system and the challenge that the prospective generation product of these systems faces are, need implementation arrives from dc extremely high-frequency tall bandwidth. This means BGA to enclose, enclose the substrate, design that encloses intermediary layer and interior to enclose wiring must can be in the mode transmission of lowermost rank moves below the mechanism.

Of high speed interface enclose wiring means

Of framework of center of new generation data move normally cannot leave to be enclosed correctly, this kind is enclosed can support basic (the ultrahigh frequency mode below TEM) mode travels. According to transmission line theory, in transmission line design, assume relevant signal travels with TEM mode, this asks to fall in the lowermost bandwidth of channel still applicable. These elements can affect signal especially the transmission behavior in enclose:

• Enclose the span between bottom BGA Bump

• The span between the Bump on semiconductor grain

• The wiring that encloses interior (cross a wiring namely)

  Redistribution layer (the measure that the interior in RDL) takes a line

Right every part of internal wiring in enclosing undertakes an analysis, can discover these elements are in where convergent, with deciding enclosed bandwidth is restricted. Want to know, the any in these elements can restrict limitative total bandwidth, restrict thereby from the frequency that encloses PCB or connector.

Consider the bandwidth of 224G channel is restricted, should use what solder ball span does not exceed 0.8 Mm to enclose dimension to support channel of 56 GHz broadband. The emulation data that this and Intel company provide and the photograph of primary consideration result that had used the integral cavity area that overshoots Kong Zhou is surrounded to reach be identical.

The solder ball that uses a bottom department is arranged undertake simple calculation, can the frequency limitation of mode of TEM of appraise cipher out. Computational process is as follows

Above all, the solder ball span of the quadrate area that uses ball of solder of X 3 of 4 solder ball, dielectric constant that encloses base material and 0.8 Mm is restricted, reach half wavelengh ends frequency:

F = (true aerial velocity of light) / [Sqrt(Dk) * 0.8mm * 2 * 2]

If substrate material is ABF, criterion Dk = 3.5, end approximately frequency is F = 50 GHz. This and the estimation value in the emulation data of 802.3 working groups and test data are similar, the cut-off that they enclose 0.8 Mm span frequency set is 59 GHz.

To enclosing interior, can use similar computational method to decide first-order (TE or TM) mode —

Assume we are divided in difference right as banding as what fluctuation uses to make an appointment with 40 micron each between ground connection plane line, what use 120 micron between enclosed barrier crossing aperture is banding line. These are banding the TEM of the line ends frequency is about:

F = (true aerial velocity of light) / [Sqrt(Dk) * 0.12mm * 2]

The result that reachs from this is 667 GHz. The actual wiring that encloses interior wants a few more complex, but the tall bandwidth that this estimates basically to the value says palpability encloses a design to be able to support. In this simple case, although banding line and the space that accept ground level are large an amount class, also can support 224G PAM-4 signal easily.

Enclose how to achieve bandwidth to restrict

Next two in, how do we achieve detailed introduction the frequency restriction that afore-mentioned TEM mode transmit.

Enclose the TEM in transmission line and blame TEM mode

Transmission line (what be used at enclosing wiring especially is banding line) size is very small, can realize very tall TEM mode bandwidth to end frequency. Next graphs are the typical wiring means of these transmission line; Include to had been in between aperture barrier among them wiring (it is poor distributinging line normally) , provide screen in order to install circuit impedance between around circuitry.

What in be being enclosed certainly, use is banding line bandwidth ends the parameter of frequency.

Using at what enclose banding in the line, decision odd root is banding bandwidth of mode of the TEM in the line ends the element of frequency applies to poor cent likewise banding line. Will poor cent is banding the line is used at speed extremely tall 224G passageway, it is to make enclose won’t from enclose substrate brim to produce intense radiation. Because the dimension of W is lesser (make an appointment with 0.1 Mm) , TEM bandwidth limitation is very tall, so the tradition is enclosed below high frequency rate to also can work well.

The TEM that solder ball span causes is restricted

In enclose, solder ball span also can produce similar bandwidth to limit effect. Because advanced processor and FPGA are tall,this is of data rate interface enclose can bring a foot to cite signal the foot to wrap inclose with ground connection. These bring a foot to be in enclosed bottom to form a coaxial to differ cent to be opposite. Bring a foot typically to arrange following plan institute to show, mark cites a base redly is the ground connection join with PCB.

Enclose solder ball typically to arrange.

Enclosing every bottom signal to cite a base is the one part with poor right cent. Signal brings the distance is the closest ground connection all round the foot to bring a foot to be in charge of deciding TEM mode ends frequency, resemble a rectangle closing it seems that because of the area all round these signal solder balls cavity, so to lesser cavity, the cut-off of mode of its lowest resonance frequency normally lower. Because cross the action of aperture to had been similar to aperture barrier,this is, they have two kinds of functions:

• signal power limitation has been in all round aperture, in order to reduce string of faze

• Influence join is enclosed and the poor cent of PCB crosses the impedance of aperture

Once signal bandwidth exceeds TEM to end frequency, partial signal will with high-ranking mode (TE or TM mode) transmission, this mode will be in different a certain weaveform appears all round the conductor that encloses area. Above all, in the area that cross a layer, every may be put in TEM mode all round root copper cash, signal of meeting block up has this kind of pattern in the bandwidth in 56 GHz above the broadband travels. In the solder ball area that encloses bottom, may put in mode of a kind of TEM, be located in enter PCB solder dish all round didymous solder ball. the contemporary ASIC with poor to be being used below 224G right cent, these two kinds of cases are not quite good.

How to evaluate enclose bandwidth

Afore-mentioned computation are a kind of rough calculation method only, will banding line or enclose Bump rectangular to be approximately wave guide. But because cross aperture / the influence of solder ball span and central conductor, enclosing wiring do not work with this kind of means actually.

The only method of electromagnetism field is to use electromagnetism field to seek solution all round affirmatory signal behavior and signal conductor implement. Use field seeks solution implement the data that computation gives, every part that encloses for 224G builds emulation model. The primary technological process of these emulation tools is as follows:

1. Consideration of use electromagnetism field is enclosed certainly as a result interrelate (Bump-to-bump) is departmental the S parameter of cent

2. Return to S parameter the network in the linear network of departmental cent

3. Can revise the linear network that extracts from inside S parameter data, in order to optimize channel model

4. But will other factor (be like balanced the transmission line that goes up with PCB) in adding a model

Can pass observation intensity mode (it is the chromatic intensity graph on 2 dimension plane normally) will observe from TEM behavior goes to those who be not TEM behavior to transfer. Next graphs are the simple give typical examples of wave guide of a rectangular medium, among them electromagnetic wave entered two kinds of different pattern (TE and TEM) .

Anyhow, interrelate in the design when geometrical structure, enclose design personnel to want to consider small loss not only, consider tall bandwidth even. Current, the main factor that limits channel bandwidth is the solder ball span that seals mount. This is meant according to rub Er is mensurable, if bandwidth increases one times again, enclose dimension to achieve a tradition possibly to enclose the limit of production technology. In think when enclosing a design, should right whole interrelate the process undertakes emulation, from enclose the Bump-to-bump inside to begin.

Enclosing is the last pace that ensures parts of an apparatus moves normally. If your design group needs understanding to enclose,design interrelate with what involve PCB and connector the interaction between, cadence Allegro X Advanced Package Designer (Allegro X APD) enclose for integrated circuit provided advanced design and analytic tool, can be designed and emulate 224G PAM-4 system, use at realizing efficient down-lead bond to design technology, tie to feel substrate to interrelate design and interrelate in detail extraction, build model and signal integrality / power supply analysis, at the same time compositive the much physics field that is used at heating up an analysis seeks solution implement, personnel of the design that help strength is active test and verify is coming loose the chip of severe exacting of hot field requirement and enclose a design.

Article origin: Cadence model ascend PCB to reach enclose resource center

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