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
>
>
>
>
>

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