[introduction] IGBT module basically is formed by a certain number of IGBT chip that mix couplet, electric join comes true through aluminous lead between chip. Standard IGBT is enclosed in, individual IGBT still is met and have diode of follow on current, be in then fill of chip upper part with many silicon gel, enclose with plastic carapace.

1, IGBT module structure

IGBT module basically is formed by a certain number of IGBT chip that mix couplet, electric join comes true through aluminous lead between chip. Standard IGBT is enclosed in, individual IGBT still is met and have diode of follow on current, be in then fill of chip upper part with many silicon gel, enclose with plastic carapace, structure of IGBT unit pile is like graph 1-1 place to show.

From go up under it is ordinal by chip, DBC (Directed Bonding Copper) and metallic heat sink (choose copper normally) 3 parts composition. DBC is formed by three-layer material, fluctuation is metallic layer two layers, intermediate layer is layer of insulation pottery and porcelain. Compare underlay of Yu Tao porcelain, the function of DBC more get the better of one prepare: It has lighter weight, better heat conduction performance, and dependability is better.

2, of IGBT enclose failure mechanism

The dependability of power parts of an apparatus is to point to fall in rated condition, parts of an apparatus finishs the capability that provides a function, express with service life normally. Because semiconductor device basically is the switch that uses implementation electricity, can produce bigger power loss, accordingly, the heat management of system of electric power electron already became the Chongzhongzhi in the design to weigh. In the working process of power electronic parts, what should answer above all is hot issue, it includes stable state temperature, temperature circulates, temperature gradient, and enclose what material falls in working temperature to match a question.

Because IGBT was adopted,fold a layer to enclose a technology, this technology not only rose to enclose density, also shortened at the same time between chip the interconnection length of lead, raised the moving rate of parts of an apparatus thereby. But also because used this structure, the dependability of IGBT got oppugn. Imagine not hard, IGBT module encloses the invalidation of class to basically happen in the joint that combines a line, chip weld, base piece weld and base piece wait for the position.

Be in normally in power loop or temperature loop, chip, solder layer, base piece, motherboard and the temperature that enclose crust to be able to experience different layer spend reach temperature gradient. Hot coefficient of expansion (CTE, coefficient Of Thermal Expansion) is the index of a main function of material, those who point to is in the temperature inside constant temperature limits every lift 1 degree, the addition of line dimension is measured be in with its the ratio of 0 degrees of length when. Graph 1-2 is the hot coefficient of expansion that middling of IGBT pile structure uses data, because the hot coefficient of expansion of respective material is different, the thermal strain between different when temperature changes material is different, because thermal stress is fatigue,the joint between mutual join layer can arise loss. Accordingly, the structural be closely bound up that the hot behavior of parts of an apparatus and module enclose. Investigation makes clear, working temperature every rise 10 ℃ , the failure rate that causes by temperature increases one times.

Graph 1-3 tagged IGBT module the dot of incidental in working process fatigue loss, specific have:

Of aluminous joint lead break away from

The diameter of the aluminous joint lead inside IGBT is 300-500um normally, their chemical composition because of the manufacturer different. However, fall in all circumstances almost, the alloy of one thousandth is joined in aluminium, for example silicon magnesium or silicon nickel alloy, aluminous hardness can promote greatly consequently corrosion resistance is able to control. As a result of the disproportionate with length and slight the temperature that depends on underlay, the voltaic capacity of joint line can drop somewhat. what the ohmic fuel factor that dc electric current gets oneself of lead of be confined to brings is fused. Because aluminous joint line is to be received directly,go up in chip or pressure bumper, can bear bigger temperature changes, and IGBT module is by different heat the material of coefficient of expansion is formed, during the job, inevitable meeting has apparent hot exhaustion. This kind of exhaustion is met the elapse as working hours, the ohmic effect of lead oneself becomes more and more evident, produce crack in ministry of bond line root eventually.

Of aluminous lead reframe

In hot loop test, of hot coefficient of expansion do not match can cause bond to the surface squashs periodicly and play litre of effect, and the adjustable limits that this kind of action is head and shoulders above material itself. Here the circumstance falls, pressure can be released through different kind, if diffuse,wriggle, grain glides, the form such as amlposition. The aluminous meeting that weigh model brings about interface of valid area decrease, bring about the addition of diamonds resistor thereby. This also explained why as periodic test, vce also shows the trend that linear raises.

Solder exhaustion and solder are interstitial

Because the solder layer between chip and underlay heats up the crack of the different generation of coefficient of expansion to be able to increase the osculatory resistance of lead, the addition of resistor can bring about the buildup of ohmic effect, make a present of of such temperature positive and negative can make crack acts more jump over intense, bring about the invalidation of parts of an apparatus eventually. The empty meeting inside solder layer affects temperature to heat up a loop, of parts of an apparatus medicinal powder hot property is reduced, this also can promote the rise of temperature, accelerate the attaint of module thereby. And, there is sluggish to answer a phenomenon between stress and meet an emergency, the loop is spent in constant ground temperature in the center, the appearance of material produces a change in real time, this increased the hot exhaustion of soldering tin again. In addition, the hot loop in the process is working during the empty meeting that technology issue introduces in soldering tin is affected, cause local temperature exorbitant, this also is a of module invalidation main reason.

Brilliant circle reachs crack of pottery and porcelain

In IGBT7 layer structure, because of heating up coefficient of expansion do not match can give each to bring very great mechanical stress. Below the circumstance of temperature difference, the deformation of each material differs somewhat, what and be the same as the difference that the different share of a material also can be distributed because of temperature cause deformation rate is different, put inevitably in local stress to pass big question so, bring about the craze of material thereby.

 

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