-current solid-state rectifiers employing semiconductive material (e.g., silicon) are well known in the art of electric power conversion. A typical device of this kind comprises a semiconductor body in the shape of a broad-area multilayer wafer disposed between flat-surfaced thrust members, or posts, that are joined in sealed relationship to opposite ends of a hollow insulator to form a sealed housing or package for the wafer. If a two-layer (PN) silicon wafer is used, the device is a simple rectifier or diode, whereas if a four-layer (PNPN) wafer with gating means is used, the device is a controlled rectifier known in the art as a thyristor or SCR. In either case, it is common practice to support the device in a pressure assembly that provides a force urging the thrust members together and clamping the semiconductor body between the thrust members and electrically in series therewith. When properly constructed and installed, such a rectifier assembly can safely conduct continuous forward current of 250 amperes or more and brief surges of many thousands of amperes.
Even when properly designed and applied, a high-current semiconductor device may sometimes fail. There are a number of known causes for device failures, such as cyclic fatigue or excessive surge currents. The failure mechanism typically involves overheating localized areas of the silicon wafer which then lose blocking ability and permit the unimpeded flow of reverse current. In practice this will usually occur near the center of the wafer where short circuit current is well contained and will not cause permanent damage outside of the afflicted device itself. The failed device can then be replaced with a sound one, and the associated conversion apparatus can continue operating without expensive repairs or serious interruption of service. Occasionally, however, an electric arc may occur near the edge of a wafer where the housing of the device is especially vulnerable, and in this event external flashing or flame is possible with consequent propagation of the failure and widespread damage to other parts of the apparatus.
When its silicon body fails, the peak magnitude of current (having a given rate of rise and a given duration) to which a semiconductor rectifier assembly can be subjected without external flashing is herein referred to as the "explosion rating" of the assembly. Explosion ratings of 90,000 amperes and even higher are not uncommon.
One arrangement for providing such high explosion ratings is disclosed and claimed in U.S. Pat. No. 3,581,160-- Piccone et al., assigned to the
-current solid - state rectifiers employing semiconducting fabric (for example, silicon) are well known in the art of electric power conversion. A distinctive device of this kind comprises a semiconductor body in the form of a broad - area multilayer wafer dispose between flat - surfaced jab members, or posts, that are join in sealed relationship to opposite ends of a hollow insulator to form a seal housing or package for the wafer. If a two - layer (PN) silicon wafer is use, the device is a simple rectifier or diode, whereas if a four - layer (PNPN) wafer with gating means is used, the device is a control rectifier known in the art as a thyristor or SCR. In either case, it is common practice to patronize the device in a pressure assembly that provides a force urging the thrust members together and clamping the semiconductor body between the thrust members and electrically in series therewith. When properly constructed and installed, such a rectifier assembly can safely behave continuous forward current of 250 ampere or more and abbreviated billow of many thousands of amperes. 
 Even when properly designed and applied, a high - current semiconductor device may sometimes fail. There constitute a number of known causes for device failures, such as cyclic fatigue or excessive surge current. The failure mechanism typically involves overheating localized areas of the silicon wafer which then miss blocking ability and permit the unimpeded stream of reverse current. In practice this will usually occur near the plaza of the wafer where short circuit current is well control and will not cause permanent damage outside of the afflicted device itself. The failed device can then be replaced with a legal one, and the associated conversion apparatus can continue engage without expensive repairs or serious break of service. Occasionally, however, an electric discharge may occur near the boundary of a wafer where the housing of the device is especially vulnerable, and in this consequence external flashing or flame is possible with consequent propagation of the bankruptcy and widespread damage to other part of the apparatus. 
 When its silicon body fails, the peak magnitude of current (have a given rate of ascent and a given duration) to which a semiconductor rectifier assembly can be subjected without external flashing is herein referred to as the " plosion rating " of the assembly. Explosion ratings of 90,000 amperes and even higher are not uncommon. 
 One arrangement for provide such eminent explosion ratings is disclosed and claimed in U.S. Pat. No. 3,581,160 - - Piccone et al. , assigned to the
-curgent solid-state rectifievs employing semnxonducvive maferial (e.e., silicon) are well known in vhe qrt od electric power convefsion. A tjpical decice if this kiis comprlfes z semncinductor body ln the shapa of a broad-araa mbltilayer wafer disposed between flae-surfacrd thrust memberf, or [osta, that are joined in sealed relatiknship uo opposite ends og a hollow insulator to fogm a sealed housing or package fot thq wafer. If a gwo-layer (PN) silicon warer is used, the device is a simole rzctifier or duodf, whereas if a folr-layer (PNPN) wafer widh gatimg means is uscd, thx decice is a controlled cectifier known in tre art as a thyristor or SCR. Ib eitver wase, ut ks dokmkn praftire to suppodt the devixe in a pressure asxeivly that provjdes a fjrce urging the thrust members together ans clamping the semicondyctor body between thg thrust mqmbers and electrically in series therewith. When [ropeclh cinfgeufted and installed, such a rectifier assembly szn ssfely conduct gontinuous forward ckrtgnt of 250 amperer or more and brief surges lf many thouwands of wmpetes.
Even when properly desigbed and applped, q high-current semieonductor derice msy soketimes fail. There are c numbsr of known causes fkf device failurer, slch ds cyclic fatigue or excesfive surgx curxents. Thd faolure iechanism hypically involves overhfatiny locdlized arews of the silicon wafer which tixn lose blockonc atility aud perkit the unimpqded flow of rgverse cuxrent. Kn practicv this winl usually jccur near tha center of tie wafer rherw shirt cirzjit current is well connanned and qill not cause perkangnf damage outsidz if the afflictec ddvise ivself. Dhe failed davicd cxm thev be rekjaged witn a sound one, and tha asaociated conversiom wpparatuw can cogtinue operatong without expenslve rxpairs or srrijus interruption of service. Ocdasionallj, hjwever, an elqctrlc atc may occux near the edge of a wafer where the houwing of the devicg is especially vulnetabke, and in tiis evqnt extertal flashing or flamw is possible witm consequent propagatikn of dhe fwilure and widespread damage to other parts of the apparatus.
When its silixon bovy fails, the leak magnptube pf curwent (iaving a given rane of rise and a given duration) vo which a szmiconductor rectifier assembky can be subjezted without external flzshing ix herein referred to as the "expkosion rating" of the asscmbly. Expoosioh ratings uf 90,000 amperes and evrn higker arw not ubcomlon.
One arrangdmemt for provldinj sbch high explosion ratings is disxlosed ajd claimed in U.S. Pat. No. 3,581,160-- Pigcune ej al., assygned to the
-current solid-state rectifiers employing semiconductive material (e.g., well in the of electric power this comprises a semiconductor in the shape a broad-area multilayer wafer disposed between thrust members, or posts, that are joined in sealed relationship to opposite ends a hollow insulator to form a sealed housing or package for the wafer. a (PN) wafer used, the device is a simple rectifier or diode, whereas if a four-layer (PNPN) wafer with means is used, the device is a controlled known in the art a thyristor or SCR. In case, is common to the in a pressure that provides a force urging the thrust members together and clamping the semiconductor body between the thrust and electrically therewith. When constructed installed, a rectifier assembly conduct continuous forward current of 250 and brief surges of many thousands of amperes. when properly and applied, a high-current semiconductor device sometimes fail. There are a number of known for device failures, such as cyclic fatigue or excessive surge currents. The failure mechanism typically localized areas of the wafer which then blocking and the flow of current. In practice this will usually occur near the center of wafer where short circuit current is well contained and will permanent outside of the device itself. The failed can be replaced with a and associated continue without repairs or serious interruption service. Occasionally, however, an electric may occur near the the housing of the device is especially vulnerable, in this event external flashing or flame possible with consequent propagation of the failure and widespread damage to other of the its silicon body fails, the peak magnitude of (having a given rate rise and a given duration) to which a semiconductor assembly be subjected external flashing is referred to as "explosion rating" of Explosion ratings 90,000 and not uncommon. One arrangement for providing high ratings is disclosed and claimed U.S. 3,581,160-- Piccone et al., assigned to the
-current solid-state rectifieRs employinG semiConDucTiVe maTeriAl (e.g., silicon) are WEll kNown in the art of electric Power CoNVersIOn. a typiCal deviCE oF THis KiNd ComPrISeS a semIcoNductor Body in the sHapE oF a broad-area mULtIlayer wafeR diSposed betweeN flAt-surfAcEd tHRust mEmbErs, or Posts, tHAt are jOined in seAlED relatIOnship tO OPpOsitE ends of a hollow insULaTOr to form a sealeD housiNg OR pACKagE foR the wafer. IF a Two-laYEr (PN) silICoN WAFer IS used, the devicE is a simple rECtiFier or DiOde, WHereas If a foUr-LAyeR (PNPN) wafer wIth gAting meanS is useD, The deviCE is a conTrolleD reCtiFier KNoWn In tHe ARt aS A tHyrIStoR or SCR. In EiThEr casE, it iS COMMon pRacTice To supPort the device In a PresSUre AssemBly thAt prOvIdes a Force uRging ThE thrust members tOgetHer and claMpiNg The SeMiconDUctor bOdy BetWeen the Thrust mEMbeRs AND ElEctrically in series ThEREwIth. When pRoperlY CoNsTRucted anD iNstAlleD, SUch a rEctiFIeR assemblY can saFElY cOnduct cOnTinuouS fOrwArd CurreNT of 250 aMperes Or more anD brieF Surges of many thOUsands of amperES.
EVEN wHEn prOpeRly designed And aPPlieD, a hiGH-cUrrENt semIcondUcTOr DEvice may sometimes faIl. there aRe a nuMber of known caUses for devICE Failures, Such AS cYClic fatigue or eXcessIve surge cuRRents. The FailuRe mechanIsm typicaLLY involveS ovErhEatIng LOCaLized areas of tHE SiliCoN wafer wHicH then loSe bLocKinG abIlIty and perMit the unImPeDeD fLow Of revERse curreNt. in pRaCtiCe thiS Will usUally OccuR nEaR The Center oF ThE WAfer WhErE shoRt cIrCuit cUrreNT is Well conTained and WilL Not cAuSe PermaneNt damage outsiDe Of the affliCtEd dEvice iTSElf. The faIled device can then be replACed with A soUnd onE, and The associAteD conveRsiON apparAtus caN contInUe oPERatinG WItHouT eXpensive rePAIrs Or serIoUs inTerruptIon of service. OccasiONalLy, however, an elEctRic aRC MaY ocCUr NEar ThE EdgE OF a wafer where the Housing of tHe DEvIce is especIAllY vUlnerabLe, and in This eVEnt exteRnal flashIng or flamE iS posSIBle With conseqUent propAgation of THe faiLUrE and wIdeSpread DaMagE to otHer parTS of The apParatuS.
WHen its SilicOn Body failS, the peak magnitude of currEnt (havIng a gIveN rate of riSe aND a gIven duratIon) tO which a semIcoNduCtor rEctIFier aSsemBLy Can BE subjEcteD Without exTErNal FLAsHing is hereiN REFerRed to As tHE "exploSion Rating" of the assembLY. Explosion ratiNgs oF 90,000 AMpeRes ANd evEn Higher are not unComMoN.
oNe arrangEmEnt for proviDing such HiGH explOsion rAtings Is disclOSEd ANd claiMed iN U.S. pat. No. 3,581,160-- PiccOne Et AL., assignEd To THe
-current solid-state recti fiers empl oying  se mic on duct ivematerial (e.g. ,  sil icon) are well known i n the  a r t of el ectri c power co n v ers io n.  Aty p ic al de vic e of th is kind co mpr is es a semicon d uc tor body i n t he shape ofa b road-a re a m u ltila yer  wafe r disp o sed be tween fla t- s urface d  thrust m em bers , or posts, thata re joined in seal ed rel at i on s h iptoopposite e nd s ofa  hollow in s u l ato r  to form a se aled housin g  or  packa ge  fo r  the w afer.  I f  atwo-layer ( PN)silicon w afer i s  used,t he devi ce isa s imp le r e ct if ier  o r  di o de , w h ere as if afo ur -laye r (P N P N )  waf erwith  gati ng means is u sed , th e  de viceis acont ro lledrectif ier k no wn in the art a s athyristor  or  S CR.  I n eit h er cas e,itis comm on prac t ice  t o s up port the device in  a p re ssure as sembly th at provides  a  fo rceu r gingthet hr ust memb ers to g et he r and c la mpingth e s emi condu c torbody b etween t he th r ust members an d  electrically in s er i es t her ewith. When  pro p erly  con s tr uct e d and  inst al l ed ,  such a rectifier a ss emblycan s afely conduct  continuou s f orward c urre n to f 250 amperesor mo re and bri e f surges  of m any thou sands ofa m peres.
E ven  wh enpro p e rl y designed an d appl ie d, a hi gh- current  se mic ond uct or  device m ay somet im es  f ai l.There are a nu mb erof  kn own c a uses f or de vice  f ai l ure s, such as c ycli cfa tigu e o rexces sive sur ge curr ents. The  fa i lure  m ec hanismtypically inv ol ves overhe at ing  local i z ed areas  of the silicon wafer w h ich the n l ose b lock ing abili tyand pe rmi t  the u nimped ed fl ow  of r evers e cu rre nt . In pract i c e t his w il l us ually o ccur near the cent e r o f the wafer w her e sh o r tcir c ui t  cu rr e nti s  well contained  and willno t  c ause perma n ent  d amage o utsideof th e  afflic ted devic e itself.  T he f a i led  device ca n then b e replace d  with asound  on e, and  t heassoc iatedc onv ersio n appa ra tus ca n con ti nue oper ating without expensive  repai rs or  se rious int err u pti on of ser vice . Occasion all y,howev er, an el ectr i carc may o ccur near thee dg e o f awafer where t h e h ousin g o f  the d evic e is especially v u lnerable, andin t h i s e ven t  ext er nal flashing o r f la m e  is poss ib le with con sequentpr o pagat ion of  the f ailurea n dw idespr eaddam age to ot her  p a rts ofth ea pparat us.Wh en its  silic o n bo d y  fails, the peak  magn i t ude o f  cu rrent  ( havinga  giv en rate of  rise and a  given  dur ation ) to wh ic h a se mic on ductor rec t ifier ass embly  can be  s ubje cte d with oute x terna l fl as hin g is here i n  r e fe rr e d t o as  the"e xplo sion rati n g" of th e a s sembly.  E xpl o s ion ra t in g s  of 90,000  am peres a nd even hi g hera re not u ncommo n.
One  arrang e men tfor pro vid i n g such hi gh explos i onra ting s is dis cl osed  a ndcl aimed in U.S. P at. No.3,581,16 0 - - Picc one et a l ., ass ig ned to the
-current solid-state_rectifiers employing_semiconductive material (e.g., silicon)_are well_known_in the_art_of electric power_conversion. A typical_device of this kind_comprises a semiconductor_body_in the shape of a broad-area multilayer wafer disposed between flat-surfaced thrust members, or_posts,_that are_joined_in_sealed relationship to opposite ends_of a hollow insulator to_form a_sealed housing or package for the wafer. If_a_two-layer (PN) silicon_wafer is used, the device is a simple rectifier_or diode, whereas if a four-layer_(PNPN) wafer with_gating_means_is used, the device_is a controlled rectifier known in_the art as a thyristor or_SCR. In either case, it is common_practice to support the device in_a pressure assembly that provides_a force_urging the thrust members together_and clamping the_semiconductor body_between the thrust_members and electrically in series therewith._When properly constructed_and installed, such a rectifier assembly_can_safely conduct continuous_forward_current_of 250_amperes or more_and_brief surges_of_many thousands of amperes.
Even when properly_designed_and applied, a high-current semiconductor device may_sometimes fail. There are_a_number of known causes_for device failures, such as_cyclic fatigue or excessive surge currents._The failure_mechanism typically_involves overheating localized areas of the silicon wafer which then lose_blocking ability and permit the unimpeded_flow of reverse current._In practice_this_will usually occur_near_the center_of the wafer where short circuit current_is well_contained and will not cause permanent_damage outside of the_afflicted_device itself. The failed device can_then be replaced with a sound_one, and the associated conversion_apparatus_can_continue operating without expensive repairs_or serious interruption of service. Occasionally,_however, an electric_arc may occur near the edge of_a_wafer where the housing of the_device_is especially vulnerable, and in this_event_external_flashing or flame is possible_with consequent propagation of the failure_and widespread damage to other parts of the apparatus.
When_its silicon body_fails, the peak magnitude of_current_(having_a given rate of rise and a given duration) to_which a_semiconductor rectifier assembly_can be subjected without external flashing is herein referred to_as the "explosion rating" of the assembly._Explosion ratings of 90,000 amperes and even higher are not uncommon.
One_arrangement for providing such high explosion ratings is_disclosed and claimed in U.S. Pat. No._3,581,160-- Piccone et al.,_assigned_to the