Folks, For those interested, I will be updating my article on MLB material selections and constructions. I've asked Daan if he would post it with my MLB ESSENTIAL STUFF. My reason for doing this simply is because too many good folks suffer at the hands of a lack of concurrence between themselves and their MLB suppliers. As I've said before, I get most of my simple jobs fixing very costly mistakes that are easily preventable using DFM/CE. In a way, I'm really tired of this kind of crap but it's a living. Anyway, for give me Peter, the following really prompted me to do this. Hope it helps: Peter, High praise in deed from someone I respect highly. First, I always get involved at the front end with "rookies" needing to learn the talk so they can walk the walk. So, it all starts with clearly defined requirements concerning what they must demand of their "qualified" suppliers (of course, I do the qualification as well). Master drawing notes, and attendant graphics and tables, not specifications, are the fundamental, key instruments supporting any contract for PCB's. Then, acceptance specifications, as IPC 600F - whatever class required, are the next requirement clearly indicating what the board shop must look for, as a function of master drawing requirements, and the methods used to determine whether drawing requirements are met. X-sectioning is one very important key for me and all I do and Section 7.0, in my notes, clearly call out this requirement and its deliverables. All this applies with rookies when I have to go in to fix a mess, which is most oftent the case these days. Concerning glass styles, you may have read one of my articles clearly indicating the importance of this critical area. The tables I sent are not revolutionary. They, along with whatever material matrix I need at the time, ensure only specified materials and constructions are used to ensure dimensional stability, bond strength, laminate integrity, and electrical performance requirements are met - exactly as I specify. If you don't have this article, I'll get it to you. As I qualify my suppliers, I have a concurrent relationship established as a function of the master drawing FIRST. If a supplier has a problem with anything on the master drawing, we discuss it. If resolution is not forthcoming, in my favor, that supplier is not qualified. This includes my dictating what glass styles and resin contents are required in each dielectric thickness as well as all the rest of the master drawin notes and graphics. Simply, with even the most qualified shops with no discredit to them, there must be no room for misinterpretation when high reliability/cost MLB's are concerned. I demand concurrence, and always get it, from our first conversations concerning a new design. With all the foregoing, I never tell or dictate to a supplier how to manage its processes though I, as part of the qualification process, know exactly what is required in accordance with the master drawing. When it comes to line widths, the supplier and myself know what is required as a function of impedance, as one example, as well as other factors such as image, etch, etc.. The latitude I allow concernis minor adjustments we both agree on before starting the fab process. I allow little lattitude concerning materials and constructions, but trace width may vary to meet a requirement though other compromises may be made as well as long as we are both clear and the requirement shows up in writing on the master drawing for that particular board. One of my most highly qualified board shops appeared to be having a solderability issue as his x'd out boards wouldn't/couldn't meet my solder wetting requirement. The "good" boards worked fine. Non wetting, it turns out, was the reason for xing out the defective boards. The master drawing notes you now attempt correcting some horrific issues on some incredibly bad designs at the most rooky of companies. I had to do something underneath the BGA's to prevent solder bridging from wave soldering operations. This is a temporary fix until we go to blind vias on this board. However, the notes clearly indicated what must be done as worked out concurrently between the shop and myself. For the reasons you stated, I am an anti tenter. I will use whatever path or process necessary to prevent using tenting and there are many alternatives - usually. The difference between core and foil lamination comes down to additional layers/costs, and a much more favorable process for most all suppliers. It is much easier and less costly to foil laminate as certain process management issues are resolved as is surfact quality with fewer pits and dents, as examples. The key is process management. If someone has never done foil lamination, don't expect them to be capable of doing anything but core processing. Quality conformance test circuitry, and the coupons comprising it, are a key element in my scheme of things. I cannot function without knowing what is in the Z axiis where 90% of the board is hidden without x-sectional analysis in accordance with IPC 6012 qualification requirements and 650 test methods indicated therein. I insist on photomicrographs before and after thermal stress. I correlate, again, all findings with master drawing reqirements thus ensuring my requirements are met and I can take the board into production expecting identical results. There's so much more but so little time. I always enjoy talking with you and learn much from your postings as well. Let me know if I can be of more assistance, Earl ----- Original Message ----- From: <[log in to unmask]> To: "Earl Moon" <[log in to unmask]> Sent: Thursday, April 25, 2002 5:34 PM Subject: Re: [TN] PREPREG > Hi, Earl, > > Very many thanks indeed for the copy of you MLB Fab spec, although it is > for class 2 boards, where mine are class 3. I am happy to see that much of > my own fab spec reflects what you have built up for yours, although mine > still lacks some of the detail you have included. > > I know little about glass styles or their properties, so have never dared > to mention requirements in my specs. How important is it to specify glass > styles that may not be used (e.g. 7628) - i.e. can that not be left to the > good sense of the fabricaor? What is te problem with7628? Is it a low resin > glass, or is there something else that makes it unsuitable for certain > aplications? > > Sorry to bug you with questions, but I would love to have greater insight > to some of this stuff. How different is a Cu-Core-Cu construction from a > foil laminated construction in terms of the end nett result? I specify the > former, but am aware that at least one fab house actually makes the boards > with foil lamination, at least for some layers. Should I be worried about > this? The boards seem to have performed OK. > > You specify the same specs for different aspects throughout your spec, > whereas I specify the specs to be complied with at the beginning of my > spec, unless otherwise stated elsewhere in the spec. Have you found it > necessary to re-state the specs for each aspect, or do you do so just to be > absolutely certain they're adhered to? Or are there options within the > specs you specify for those aspects, and you're stating your requirement or > preference? > > I have never stated what the trace widths and spacings should be, allowing > the Gerber data to speak for itself. Should I be stating them in writing as > well? > > Aren't etchback and desmear "givens" these days, or should they still be > stated in Black and White? > > I haven't requested test coupons or other proof of compliance apart from a > C of C, mostly because we have no facilities here for checking them > ourselves. Only when we have a known fab problem will I ask for these. Nor > have I thought to specify solderability requirements, and proof thereof. > (You see, I do have a bit to learn!) > > I see you use tenting - I mention this only because of the debates that > arise on TN frequently about this with regard to contamination entrapment > and reduced cleaning effectiveness with this method. I have considered > tenting inadvisable for Class 3 boards, have specifically recommended to > the design team that it not be used (not that they know to specify it one > way or the other anyway). In your experience, tenting is obviously not a > problem, or has particular benefits or you wouldn't be including it in your > notes. Can you tell me the rationale behind using or not-using tenting, > apart from not losing solder down holes and minimising the risk of "double > reflow" (that phrase so hated by the redoubtable Sir GW)? > > Large respect > > Peter > > > > "Earl Moon" <[log in to unmask]> 25/04/2002 08:54 PM > > To: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group@ST > Domain > cc: > Subject: Re: [TN] PREPREG > > > > > --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------