Bill and Matthew !
As manufacturer of ENTEK finished boards I would like to add some comments :
> At 11:36 05/12/97 -0800, you wrote:
> Matthew:
> From my perspective, the question that needs to be addressed FIRST is
> where in the process is the ENTEK applied to the board.
>
> 1) ENTEK BEFORE or AFTER Bare Board Test
>
> By itself, ENTEK is an insulator. Therefore, if it is applied PRIOR
> to bare board testing, the bare board test probes can create "false
> opens" due to residue buildup on the tips of the probes. This
> might indicate that ENTEK AFTER bare board test would be better.
If ENTEK finished board will be tested with ENTEK on it , the bare board
tester will damage the the coating at contact points ( otherwise there will
be no contact ) , therefore all contact points will not be protected anymore
. During soldering strange things might happen .
>
> On the other hand, a mild microetch is used to prepare the surface
> prior to ENTEK application. If the dip process is used and the
> microetch is fresh (i.e. strong solution), excessive etching can
> result. This can result in circumferential barrel voids at the
> knee of the holes, where the copper is the thinnest. If ENTEK is
> applied AFTER TEST, this type of defect will not be discovered
> until the board has been populated with expensive components.
>
> Some people subscribe to the policy "NO chemical operation shall be
> performed AFTER bare board testing". Each vendor's process and
> controls must be evaluated to assess the likelihood for this type
> of failure.
Hold Your horses ! Normal microetch applied before ENTEK application should
remove 1 to 1.5 microns . I someone is manufacturing boards of such quality
, that the boards can be damaged by such microetch , I will make no
difference , because the boards will end up without copper in the holes or
knee . Just imagine what will happen with such copper thickness during
solderig - simple crack . Juct to finish this point : I don`t know what is
worst : uncontrolled microetch or very thin and poor copper distribution .
From the point of the end user it will not make a big difference .
>
> 2) In-line vs. Batch
>
> In my opinion, in-line would be better and more repeatable, if the
> total volume of boards that the vendor processes warrant the
> equipment expense. Properly managed, the dip process will work.
Unproperly managed in - line and dip will be similar . The only diference is
, than those from in line will more consistently out of spec than from dip
process .
>
> 3) "Spotted" Boards:
>
> Another "problem" to look out for is moisture spotting during
> shipment. ENTEK uses a DI rinse in the process and, if vias are
> small (0.013" dia.), moisture can be trapped inside the barrel of
> those vias. Placing the "drip-dried" board in a plastic bag for
> shipment, can result in residual moisture STILL residing in the
> bag. Shipment of the boards to the final destination (shipping
> vibration, change in temperature, etc.) causes the moisture to
> migrate to the inside surface of the bag and, in turn, back onto
> the board. The thickness of the ENTEK on the board will be reduced
> where there is intimate moisture contact. The appearance looks like
> "water spots" on a drinking glass. They COULD result in localized
> ENTEK "voids" and potentially cause solderability problems, if the
> boards are left on the shelf for an extended period of time.
>
> One test for "dryness" of a board is a deceptably simple one:
>
> a) Take a piece of colored construction paper (or the cardboard
> stiffener on the back of a pad of paper) that will darken when
> exposed to water and place it on a flat surface (e.g. table).
>
> b) Take a "dry" board and firmly slap the face of the board onto
> the cardboard. If it shows dark spots on the cardboard when the
> fab is removed, the fab is NOT dry and could caule spotting
> during shipment.
>
> My suggestion is to have the boards BAKED after ENTEK to eliminate
> this potential problem.
Be carefull about baking . ENTEK change degree of polimerisation after
baking resulting :
a ) reduction in numbers of soldering cycles that ENTEK is able to stand
b ) different behaviour regardind fluxes and solder pastes .
Ask ENTONE advice .
>
> I advocate the use of ENTEK for fine pitch QFP designs, because of the
> resultant pad flatness, as compared with HASL. However, it does have
> some "side effects" to watch out for. It is NOT the "panacea for all
> ills", but it is better than some of the alternatives in certain
> designs.
>
> The above opinions are my own, etc.,etc., etc.
>
> Good Luck!
>
> Bill Fabry
> Plantronics, Inc.
> (408) 458-7555
>
> e-mail: [log in to unmask]
>
>
>______________________________ Reply Separator
_________________________________
>Subject: [TN] entek plus process
>Author: "TechNet Mail Forum." <[log in to unmask]> at INTERNET
>Date: 12/5/97 9:58 AM
>
>
>I am getting confusing responses from a board vendor that
>uses in-line process, and from a board vendor that uses
>dipping process to coat boards with Entek Plus.
>
>What are advantage/disavantage using either process?
>
>What are problem associated with boards that were
>fabricated using dipping process?
>
>Does in-line processing provide better consistent and
>controllable coating (typ: 0.35um) than dipping process?
>
>Is there any other coating thickness measurement technique
>used by board vendors other than the sampling method
>specified by Enthone using UV spectrophotometer?
>
>What are some of inspection method employed by board
>vendors to check boards are coompletely dry prior packaging
>and shipping?
>
>advance thanks
>regards
>Matthew
>
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>
Edward Szpruch
Eltek Ltd - Israel
Tel 972 3 9395050
Fax 972 3 9309581
E-mail : [log in to unmask]
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