Hi Bill,
I have been advised by Enthone in the past not to bake boards as it
removes the organic coating...even at 80 deg. C for 2 hours is
detrimental.... This was in relation to Entek 106A
Marcelo
> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Friday, December 05, 1997 2:36 PM
> To: [log in to unmask]
> Subject: Re: [TN] entek plus process
>
> 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.
>
> 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.
>
> 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.
>
> 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.
>
> 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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