ems with the=0APTVs, but it is not a given. A higher Tg certainly helps= =97and I have been told=0Athat higher Tg materials do NOT carry a cost pr= emium. A lot will depend on the=0Aquality of your PTVs in terms of platin= g thickness, plating uniformity,=0Atensile strength and ductility of the = Cu deposit inside the PTV. You also did=0Anot say whether you have any ma= nual soldering operations (they are worse than=0AHASL or reflow) as well = as the severity of the use environment of your=0Aproduct.=0AYou may want = to take a look at Appendix B in IPC-D-279, 'Design Guidelines for=0ARelia= ble Surface Mount Technology Printed Board Assemblies' for more=0Ainforma= tion. =0AOn hole breakout the necessary information is not yet in. some t= ime ago, there=0Awas an ITRI report and significant discussion on the Tec= hNet on the subject of=0Anon-functional landswhich is a related subjest m= atter and which I am sending=0Ayou below:=0AThis is from the IPC News Rel= eases dated 6/26/97:=0AITRI STUDY: REQUIREMENT FOR ANNULAR RING WASTES MI= LLIONS=0ANorthbrook, IL 6/26/97=0AThe printed wiring board (PWB) industry= loses more than $70 million annually=0Ain boards discarded due to hole-t= o-land misregistration. The Interconnect=0ATechnology Research Institute = (ITRI) created an Improved Registration Project=0ATeam to investigate the= problem, and has just made the report on its findings=0Aavailable for pu= rchase.=0AIn its report, PWB Hole-To-Land Misregistration: Causes and Rel= iability,=0AProject Final Report, the team concluded The requirement for = an intact annular=0Aring at every innerlayer pad is excessively conservat= ive. "This study=0Ademonstrates that the requirement prohibiting breakout= should be changed to=0Aone that maintains a minimum spacing to adjacent = circuits," says Marshall=0AAndrews, Chief Executive Officer of ITRI. "Thi= s change will allow PWB=0Afabricators and their customers to save million= s of dollars while improving=0Aboard routability."=0AThis conclusion culm= inates two years of research by ITRI. The project team=0Acreated a PWB te= st vehicle that was designed to have different degrees of pad=0Abreakout = from none to just a plated hole in a circuit line with no pad. Hole=0Arel= iability tests were conducted by thermal cycling the boards from -65 to= =0A+125 degrees centigrade. No failures due to the line to barrel connect= ion were=0Afound even after 1000 cycles, 10 times the specification requi= rement.=0AFor more information on the report, or ordering instructions, c= ontact Diana=0AHempstead, Administrator, at ITRI at (512) 833-9930, fax q= uestions to (512)=0A833-9925, or e-mail [log in to unmask] is an= industry-led consortium for collaboration among the electronic=0Ainterco= nnection industry, government and academia. Its purpose is to enhance=0At= he global competitiveness of the North America electronics interconnectio= n=0Aindustry by enabling collaboration among its members to accelerate de= velopment=0Aand application of revolutionary and evolutionary technology.= =0ASeeking data/reports to address questions on the risks associated with= Annular=0ARing size. In particular, as the mis-registration of the of t= he mechanical=0Adrill to the PTH Pad moves towards a trace leading into t= he pad the potential=0Afor an 'open' to occur increases. Concerns center= around 'thin' ring passing=0AET, but in field stresses cause fracture an= d crack propagation to 'open'=0Astate.=0AThanks, Chris [Chris_Gardini-ECG= [log in to unmask] (Chris Gardini-ECG005)]=0A=0AChris,=0908/22/97=0AITRI (= The Interconnect Technology Research Institute) recently published=0Arepo= rt that addresses your concerns. In essence they found that a PTH without= =0Aannular ring is as reliable as a pad with a large annular ring. Sampl= es were=0Asubmitted from several PWB manufacturers and the thermal cycle = testing was=0Aperformed by NIST or Crane. Any way I'm sure you can get th= e report either=0Afrom ITRI in Austin, Texas or from the IPC=0ADavid Ariv= ett [[log in to unmask] (David Arivett)]=0ACuplex Inc.=0A=0AHi= Chris,=0AIf you get the ITRI Report 'PWB Hole-To-Land Misregistration: C= auses and=0AReliability, Project Final Report", you may be a little caref= ul in applying=0Athe conclusions. I am not saying that the conclusions ar= e wrong, but that=0Abased on the test performed, the conclusions may be a= stretch. From a=0Areliability point-of-view of the PTH barrel-to-land in= terconnect, the most=0Asevere loading occurs during excursions to solderi= ng temperatures not thermal=0Acycling, even from -65 to +125C. That is be= cause the largest thermal expansion=0Aof the epoxy that causes the radial= barrel compression and land rotations=0Aoccurs only at temperatures abov= e Tg.=0AWerner Engelmaier=0A=0AHi Chris -- I agree with Werner. The Z-ax= is stress is the concern which=0Anormally occurs, above the 125C tg, at s= oldering temperatures, around 260C. A=0Asecond point to consider is the s= olderability issue. The annular ring aids in=0Athe transfer of heat to th= e solder joint especially for hand soldering during=0Aassembly or field r= epairs.=0Aregards,=0AArny Andrade [[log in to unmask]]=0ASandia Labs/= ret.=0908/25/97=0A=0AHi Werner,=0908/27/97=0AYour comments to Chris were = interesting and I agree for the most part, but I=0Ahave a question with r= egard to the comment about radial barrel compression=0Aduring elevated te= mperatures. It is my understanding that as the board expands=0Ain X & Y t= hat the hole will also increase in diameter. Due to the=0Adisproportionat= e difference in CTE I would expect that the barrel would be in=0Atension = and not in compression (a hoop stress). This phenomena has been=0Ademonst= rated in the Physics classroom on many occasions with Ring and Ball=0Aapp= aratus. It's good to see you responding to some of these interesting=0Apr= oblems showing up on Technet. So what do you think about this analysis?= =0ALes Connally [[log in to unmask]]=0A=0AHi Les,=0AI don't know= about the 'Ring and Ball' experiment, but I do know what happens=0Ainsid= e a PWB around the PTHs during heating to solder temperatures.=0A(1) At t= hose temperatures the epoxy is way above its Tg, is very soft, and=0Ashou= ld be considered a high-viscosity liquid as far as behavior is concerned.= =0A(2) For analysis as to what is going on around a PTH, the PWB can be= =0Aconsidered an infinite plane in the x- and y-directions.=0A(3) While t= he epoxy tries to expand in all directions, it is constrained in=0Athe x,= y-directions by the glass reinforcements.=0A(4) Thus, the primary expansi= on is in the z-direction at roughly 3 times the=0Alinear thermal expansio= n, because all the volumetric expansion is funneled=0Ainto the z-directio= n.=0A(5) The PTH hole, however, allows the epoxy to also expand into the = space=0Aoccupied by the PTH if the PTH barrel wall is thin enough to by c= ompressed.=0AThat is why in cross-sections of PTHs with 1 mil of copper p= lating and less,=0Aone sees the PTH barrel bowed inward between innerlaye= r lands, particularly in=0Aprepreg layers (higher resin content, less cur= e) and when there are larger=0Adistances between lands (no non-functional= lands), and sometimes a space=0Abetween the barrel wall and the receded = epoxy. If there were no copper=0Aplating, the hole diameter would decreas= e on heating.=0A(6) Thus, the PTH barrel in tension in the z-direction, w= ith the largest=0Astresses near the PWB center, the PTH barrel experience= s compressive hoop=0Astresses, innerlayer lands experience tensile stress= es at their attachment to=0Athe PTH barrel, and innerlayer lands near the= PWB surface experience bending=0Amoments due to land rotation resulting = from the z-direction expansion of the=0Aepoxy surrounding the PTH barrel.= =0AWerner Engelmaier=0A=0AHi Ken & Richard,=0908/29/97=0AThis has been a = long ongoing debate. =0AThe work done for IPC-TR-579, 'Round Robin Reliab= ility Evaluation of Small=0ADiameter Plated Through Holes in Printed Wiri= ng Boards', indicated a small=0Aimprovement in reliability with the prese= nce of functional and non-functional=0Ainnerlayer lands. This was NOT a m= ajor finding of this study, nor was it a=0Arecommendation for the use of = non-functional innerlayer lands. =0AThe results of the just released ITRI= Report, 'PWB Hole-to-Land=0AMiregistration: Causes and Reliability', giv= e the same indication (Note:=0Aessentially all the failures come from one= PWB manufacturer, primarily from=0APTV barrel cracking, before the test = was stopped at about 1100 cycles; the=0Aother manufacturers show some int= erconnect separations of the innerlayer trace=0Afrom the barrel). The 199= 7 ITRI report also shows the vast improvement in the=0Aquality of PTV str= uctures since the 1988 IPC-TR-579 study. =0AThe ITRI study was done with = temperature cycling from -65<->+125C; thus, the=0Areliability results dir= ectly, on an accelerated basis, relate to the thermal=0Acycling PWBs see = in product operation. However, because no excursions were=0Ataken to sold= ering temperatures, where because of being above Tg of the epoxy=0Asignif= icantly more thermal expansion mismatch occurs and the epoxy is much=0Aso= fter, the results can not be assumed to be representative of what might= =0Ahappen during PWB assembly. It is during solder temperature excursions= that=0Athe compressive hydro-static hoop stresses act on the PTV barrel = and that=0Asurface and innerlayer land rotations occur. These represent q= uite different=0Aloading conditions than -65<->+125C temperature cycling,= and may produce=0Adifferent conclusions.=0ACONCLUSIONS: Non-functional l= ands are not likely worth having, because the=0Asmall potential reliabili= ty gain for high-reliability PTV structures for most=0Aapplications is no= t worth the manufacturing difficulties and costs that have=0Abeen encount= ered. Misregistration and the absence of annular rings are no=0Asignifica= nt reliability threat to PTV barrels. Assuming, that the behavior=0Adurin= g solder temperature excursions is not dramatically different and the PTV= =0Ainterconnect structure survives assembly, misregistration and the abse= nce of=0Aannular rings are no significant reliability threat to PTV inter= connects=0A(Interconnects can be protected from large loads by having a 9= 0 degree trace=0Ajog just before the PTV, i.e. do not approach the PTV wi= th a long straight=0Atrace).=0AWerner Engelmaier=0A=0AWerner Engelmaier= =0AEngelmaier Associates, L.C.=0AElectronic Packaging, Interconnection an= d Reliability Consulting=0A7 Jasmine Run=0AOrmond Beach, FL 32174 USA= =0APhone: 904-437-8747, Fax: 904-437-8737=0AE-mail: [log in to unmask] ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. 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