Any coming loose the target of hot solution is to ensure the working temperature of equipment does not exceed the security that its manufacturer provides to be restricted to be worth. In electronic industry, this job temperature is called the “ knot lukewarm ” of parts of an apparatus. For example, in processor, what point to on this term literal is electric energy changeover writtens guarantee for caloric semiconductor.

 

To hold the job, quantity of heat must written guarantee with ensuring lukewarm rate pours out of semiconductor acceptabilitily. When the knot that encloses from whole parts of an apparatus when thermal current is in shift, this kind of thermal current encounters resistance, like resistance is being faced when shedding lead like the electron. In thermodynamic respect, this kind of resistor calls electric resistor, divide composition by a few ministries. Begin from node, quantity of heat can flow to the housing of component, can place radiator. This is called ΘJC, or the knot comes the thermal resistance of housing. Quantity of heat also can be poured out of from the coping surface of package and flow into board in. This is called to written guarantee circuit board resistor, or ΘJB

 

ΘJB definition arrives from node only to should heat up method when circuit board, node is mixed the difference in temperature between circuit board is divided with power. To measure ΘJB, the coping of parts of an apparatus is insulation, cold board receive circuit board brim repeatedly (graph 1) . This is true thermal resistance, this is the character of parts of an apparatus. Only question is, in applying actually, people did not know to transmit how many power from different method.

 

Graph 1: Cross section pursues annular cold board RΘJB 2.

 

ΨJB is to use many conduct heat the magnanimity of the difference in temperature when method, for example the flank of package and coping board of directors. These much method are some of the solid in effective system, must use carefully measure.

 

Because there is many to conduct heat inside package method, singular resistance cannot be used at mathematical calculation the knot is lukewarm. Arrive from the knot environmental thermal resistance must farther fractionize is resistor network, in order to improve a tie lukewarm the precision that forecast. Simplifying resistor network is shown 2 times like the graph.

 

Graph 2: The knot comes environmental resistor network.

 

The person such as Joiner 1 finished previous work ΘJMA and circuit board temperature is relevant couplet (see formula 1) . ΘJMA is to be in evaluate all conducting heat the total thermal resistance that the environment goes to from the knot when method. Below this kind of circumstance, ΘCA expresses by the interfacial resistor between radiator thermal resistance and parts of an apparatus and receiver.

 

Watch 1 listed the JEDEC parameter of typical BGA component. These in computation of the following give typical examples using:

 

The node of thermal resistance of ΘJMA= mobile air

 

ΘJB= knot comes the thermal resistance of circuit board

 

ΘJC= knot comes the thermal resistance of housing

 

Thermal resistance of ΘCA= Case environment

 

TBA = circuit board temperature rise

 

Parameter specification is worth – of unit ΘJC thermal resistance

 

The knot arrives – of crust 0.45°C/WΘJB thermal resistance

 

The knot comes lukewarm 105°C of highest knot of 20 W Tj of power of hot design of circuit board 2.6°C/W TDP

 

Express 1: Typical heat encloses norms

 

As circuit board layout becomes more and more concentrated, need design be sent on a diplomatic mission is spent and likely of little space optimize medicinal powder hot solution. In short, the radiator that allows excessive design without surplus has close together component span. The influence of consideration board coupling is this kind of optimized substantial. In the consideration only bear case arrives of housing conduct heat existence of the ability when method uses the possibility that exceeds large size radiator.

 

The 105°C written guarantee that issues in 55°C environment temperature to ensure is lukewarm, typical component (see a table 1) the radiator resistor that needs 2.05°C/W (if oversight circuit board guide) . When the consideration circuit board guides when connecting, suppose circuit board temperature and air temperature are identical, concrete ties Wen Ke can be low to 74°C. This states carbon fin is more than necessary temperature.

 

Can see from this example, what must consider to come from component to connect contact is all conduct heat method. Use ΘJC and ΘCA value to may be brought about only be more than first-rate radiator, and likelihood cannot accurate forecast the job the knot is lukewarm. The dependency of use proposal also can forecast the knot from circuit board temperature is informed in the experiment lukewarm, if pursue,3 are shown.

 

Graph 3: Circuit board temperature is elevatory lukewarm to the knot influence.

 

When be put in many component, the situation becomes more complex than using the discrete component on circuit board only much. Existence conducts coupling between the package that adopts PCB, and the radiate between package and photograph adjacent card and convection coupling. Pursue the 4 simple PCB that showed one contains two element. The power comsumption of two component assumes for P1 and P2, and assume we are negligible radiation conducts heat. The circuit below every parts of an apparatus board temperature is Tb1 and Tb2 respectively. We still assume the transverse resistor between on circuit board two component is θb1b2.

 

Graph 4: Have the simple principle plan of the PCB of two component.

 

Graph 5: Have the simple resistor network of the PCB of two component.

In node J1, j2 place applies energy balance, b1 and B2:

 

 

Have 4 equation and 4 unknown number: Tj1, tj2. Tb1 and Tb2. Unknown can pass the simultaneous equations that seek solution to decide. This simple case makes clear, through conducting method coupling two component, find a form lukewarm meeting becomes complex much. In applying actually, should encounter the many package that have different and electric plane and when many PCB, the case is more complex than afore-mentioned give typical examples much, all electric plane are passed conduct, convection and radiation interaction.

 

To achieve reasonable result, stylist must use reasonable project judgement to differ approximately the coupling between package. This can pass the following method to come true:

Methodological 1 – uses the analytic model that controls bulk law or resistor network model. Need of this kind of method is excessive simplify problem; otherwise the solution becomes very complex and highbrow.

 

Methodological 2 – is in simplify CFD is used on geometry, like Guenin [4] be narrated. This method shows the equivalent of package expresses an area to be:

 

 

Among them the equivalent that An is package occupies an area, pn is the power comsumption of package, PTotal is total power comsumption, ATotal is the total area of PCB. After computational equivalent occupies an area, can use CFD imitate to have the simple PCB of the discrete component that occupies an area An and power comsumption to be 1 tile. This process can be calculated effectively circuit board temperature and environmental temperature (θBA) the poor value between, power comsumption is 1 tile. Graph the 6 CFD simulation that showed a such cell, graph the 7 function that showed θBA regards PCB as dimension. Graph 7 can use at the θBA that through simple calculation its cover an area of an area effectively to decide other component. Assume all component are had occupy an area identically.

 

Graph 6: The CFD imitate of single component on PCB

 

Graph 7: The ΘBA that regards PCB dimension as the function of 4 distributings.

 

Circuit board temperature can calculate as follows:

 

 

Written guarantee Wen Ke is with computation:

 

 

Among them ψJB is diagnostic parameter.

 

Methodological 3 – if PCB is usable, measure TB of circuit board temperature through the experiment, use formula 8 will search a knot lukewarm. Same, this is approximation, because coupling of parts of an apparatus arrives,the condition of PCB may check with JEDEC board use condition is completely different.