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Deionized Water - Cleaning PCBs

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  • Syd Levine (AnaLog)
    I discoverd my problem, I think. I have been trying to use grocery store (Wal-Mart) distilled water to wash these dern PCBs. At 150C, the ionic residue is
    Message 1 of 10 , Feb 28, 2003
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      I discoverd my problem, I think. I have been trying to use grocery store
      (Wal-Mart) distilled water to wash these dern PCBs. At 150C, the ionic
      residue is causing trouble. Where can I find good DI water in bottles? I
      hate to invest in a machine when I need maybe a gallon or two per week. I
      suspect I need water that is close to the chip making standards (18
      megohm/cm).

      Syd H. Levine
      AnaLog Services, Inc.
      Phone: 270-276-5671
      Telefax: 270-276-5588
      E-mail: analog@...
      URL: www.logwell.com


      --
      Author: Syd Levine \(AnaLog\)
      INET: AnaLog@...

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    • Fred Townsend
      The over the counter variety is probably only single distilled if distilled at all. Laboratory water is triple distilled. Sounds like you are really buying DI
      Message 2 of 10 , Mar 1, 2003
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        The over the counter variety is probably only single distilled if distilled at
        all. Laboratory water is triple distilled. Sounds like you are really buying
        DI water instead of distilled. Sometimes the bottle says something like "For
        all distilled water uses" meaning it is a substitute.

        There are simple DI cartridges that can be coupled to your tap. They are
        cheap. Simple softeners do not remove the light metals. Be sure to get what
        is called a double ion exchange resin. I think I got mine from Vanwaters
        Rogers.

        BTW do you bake your PCBs after you wash them?

        Fred Townsend


        "Syd Levine (AnaLog)" wrote:

        > I discoverd my problem, I think. I have been trying to use grocery store
        > (Wal-Mart) distilled water to wash these dern PCBs. At 150C, the ionic
        > residue is causing trouble. Where can I find good DI water in bottles? I
        > hate to invest in a machine when I need maybe a gallon or two per week. I
        > suspect I need water that is close to the chip making standards (18
        > megohm/cm).
        >
        > Syd H. Levine
        > AnaLog Services, Inc.
        > Phone: 270-276-5671
        > Telefax: 270-276-5588
        > E-mail: analog@...
        > URL: www.logwell.com
        >
        > --
        > Author: Syd Levine \(AnaLog\)
        > INET: AnaLog@...
        >
        > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
        > San Diego, California -- Mailing list and web hosting services
        > ---------------------------------------------------------------------
        > To REMOVE yourself from this mailing list, send an E-Mail message
        > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
        > the message BODY, include a line containing: UNSUB CHIPDIR-L
        > (or the name of mailing list you want to be removed from). You may
        > also send the HELP command for other information (like subscribing).


        --
        Author: Fred Townsend
        INET: fred@...

        Fat City Network Services -- 858-538-5051 http://www.fatcity.com
        San Diego, California -- Mailing list and web hosting services
        ---------------------------------------------------------------------
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        also send the HELP command for other information (like subscribing).
      • Syd Levine (AnaLog)
        These are getting baked after washing as part of the testing routine. These boards have to be able to go to 150C, and really need to go to 175C. Would
        Message 3 of 10 , Mar 1, 2003
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          These are getting baked after washing as part of the testing routine. These
          boards have to be able to go to 150C, and really need to go to 175C. Would
          soaking them in the distilled water help get the ionic residue off em. I
          don't seem to be able to get rid of all of it.

          > BTW do you bake your PCBs after you wash them?
          >
          > Fred Townsend
          >
          >
          > "Syd Levine (AnaLog)" wrote:
          >
          > > I discoverd my problem, I think. I have been trying to use grocery
          store
          > > (Wal-Mart) distilled water to wash these dern PCBs. At 150C, the ionic
          > > residue is causing trouble. Where can I find good DI water in bottles?
          I
          > > hate to invest in a machine when I need maybe a gallon or two per week.
          I
          > > suspect I need water that is close to the chip making standards (18
          > > megohm/cm).
          > >
          > > Syd H. Levine
          > > AnaLog Services, Inc.
          > > Phone: 270-276-5671
          > > Telefax: 270-276-5588
          > > E-mail: analog@...
          > > URL: www.logwell.com
          > >
          > > --
          > > Author: Syd Levine \(AnaLog\)
          > > INET: AnaLog@...
          > >
          > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
          > > San Diego, California -- Mailing list and web hosting services
          > > ---------------------------------------------------------------------
          > > To REMOVE yourself from this mailing list, send an E-Mail message
          > > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
          > > the message BODY, include a line containing: UNSUB CHIPDIR-L
          > > (or the name of mailing list you want to be removed from). You may
          > > also send the HELP command for other information (like subscribing).
          >
          >
          > --
          > Author: Fred Townsend
          > INET: fred@...
          >
          > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
          > San Diego, California -- Mailing list and web hosting services
          > ---------------------------------------------------------------------
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          > the message BODY, include a line containing: UNSUB CHIPDIR-L
          > (or the name of mailing list you want to be removed from). You may
          > also send the HELP command for other information (like subscribing).
          >


          --
          Author: Syd Levine \(AnaLog\)
          INET: AnaLog@...

          Fat City Network Services -- 858-538-5051 http://www.fatcity.com
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        • Kai Klein
          Hi, may I missed something, has someone made a test with a ultrasound cleaner and the cleaning liquids. and made a ultrasound cleaning machine by him self ? I
          Message 4 of 10 , Mar 1, 2003
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            Hi,

            may I missed something, has someone made a test with a ultrasound cleaner
            and the cleaning liquids.

            and made a ultrasound cleaning machine by him self ? I need a schematic for
            such a machine.

            Kai Klien

            ----- Original Message -----
            To: "Multiple recipients of list CHIPDIR-L" <CHIPDIR-L@...>
            Sent: Saturday, March 01, 2003 12:59 PM


            >
            > These are getting baked after washing as part of the testing routine.
            These
            > boards have to be able to go to 150C, and really need to go to 175C.
            Would
            > soaking them in the distilled water help get the ionic residue off em. I
            > don't seem to be able to get rid of all of it.
            >
            > > BTW do you bake your PCBs after you wash them?
            > >
            > > Fred Townsend
            > >
            > >
            > > "Syd Levine (AnaLog)" wrote:
            > >
            > > > I discoverd my problem, I think. I have been trying to use grocery
            > store
            > > > (Wal-Mart) distilled water to wash these dern PCBs. At 150C, the
            ionic
            > > > residue is causing trouble. Where can I find good DI water in
            bottles?
            > I
            > > > hate to invest in a machine when I need maybe a gallon or two per
            week.
            > I
            > > > suspect I need water that is close to the chip making standards (18
            > > > megohm/cm).
            > > >
            > > > Syd H. Levine
            > > > AnaLog Services, Inc.
            > > > Phone: 270-276-5671
            > > > Telefax: 270-276-5588
            > > > E-mail: analog@...
            > > > URL: www.logwell.com
            > > >
            > > > --
            > > > Author: Syd Levine \(AnaLog\)
            > > > INET: AnaLog@...
            > > >
            > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
            > > > San Diego, California -- Mailing list and web hosting services
            > > > ---------------------------------------------------------------------
            > > > To REMOVE yourself from this mailing list, send an E-Mail message
            > > > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
            > > > the message BODY, include a line containing: UNSUB CHIPDIR-L
            > > > (or the name of mailing list you want to be removed from). You may
            > > > also send the HELP command for other information (like subscribing).
            > >
            > >
            > > --
            > > Author: Fred Townsend
            > > INET: fred@...
            > >
            > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
            > > San Diego, California -- Mailing list and web hosting services
            > > ---------------------------------------------------------------------
            > > To REMOVE yourself from this mailing list, send an E-Mail message
            > > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
            > > the message BODY, include a line containing: UNSUB CHIPDIR-L
            > > (or the name of mailing list you want to be removed from). You may
            > > also send the HELP command for other information (like subscribing).
            > >
            >
            >
            > --
            > Author: Syd Levine \(AnaLog\)
            > INET: AnaLog@...
            >
            > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
            > San Diego, California -- Mailing list and web hosting services
            > ---------------------------------------------------------------------
            > To REMOVE yourself from this mailing list, send an E-Mail message
            > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
            > the message BODY, include a line containing: UNSUB CHIPDIR-L
            > (or the name of mailing list you want to be removed from). You may
            > also send the HELP command for other information (like subscribing).
            >

            --
            Author: Kai Klein
            INET: Kai.Klein@...

            Fat City Network Services -- 858-538-5051 http://www.fatcity.com
            San Diego, California -- Mailing list and web hosting services
            ---------------------------------------------------------------------
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            also send the HELP command for other information (like subscribing).
          • TQuiroz@aol.com
            I don t know the difference between de-ionized water and mineral-free water, but I just bought PEAK mineral-free water for batteries and radiators at my local
            Message 5 of 10 , Mar 1, 2003
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              I don't know the difference between de-ionized water and mineral-free water, but I just bought PEAK mineral-free water for batteries and radiators at my local Pep Boys auto parts store. The jug label does not have any specs.
              Hope this helps,

              Tony
            • Syd Levine (AnaLog)
              Interesting, I will check that out. Thanks! ... From: TQuiroz@aol.com To: Multiple recipients of list CHIPDIR-L Sent: Saturday, March 01, 2003 9:43 PM
              Message 6 of 10 , Mar 1, 2003
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                Interesting, I will check that out.  Thanks!
                ----- Original Message -----
                Sent: Saturday, March 01, 2003 9:43 PM
                Subject: Re: Deionized Water - Cleaning PCBs

                I don't know the difference between de-ionized water and mineral-free water, but I just bought PEAK mineral-free water for batteries and radiators at my local Pep Boys auto parts store. The jug label does not have any specs.
                Hope this helps,

                Tony
              • Fred Townsend
                Syd, I think you raise a number of issues. My studies way back in the early 1970s showed FR4 started out gassing and changing composition at 130C. Some of the
                Message 7 of 10 , Mar 2, 2003
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                  Syd, I think you raise a number of issues. My studies way back in the early
                  1970s showed FR4 started out gassing and changing composition at 130C. Some of
                  the breakdown products were very acidic. Perhaps this is a decomposition issue
                  rather than an ionic contamination issue. Are you using high temperature
                  laminates or ordinary FR4?

                  BTW much later studies in the late 90s showed that polyamide boards were
                  slightly lower in leakage at room temperature but considerably better at high
                  temperatures. I don't recall at how high a temperature I tested.

                  "Syd Levine (AnaLog)" wrote:

                  > These are getting baked after washing as part of the testing routine. These
                  > boards have to be able to go to 150C, and really need to go to 175C. Would
                  > soaking them in the distilled water help get the ionic residue off em.

                  I'm inclined to believe that long term soaking is not a good idea. Most
                  contaminates go into solution quickly so soaking is probably not necessary. A
                  lot would have to do with the quality of plated through holes (PTH) in the PCB.
                  If the holes are rough the plating may have voids or fissures that could trap
                  contaminates in the glass fiber within the PCB. When the board is heated these
                  fissures will spread the contamination back on the board surface.

                  There is another issue. Ions conduct but so do metals and carbon, silicon etc.
                  Do you know for sure you have an ionic contamination issue?

                  Still another issue. DI water is free of ions but not necessarily free of
                  organic compounds. Distilled water is free from both ions and organic material
                  but very quickly turns acidic when exposed to air due to CO2 absorption. I used
                  DI water in combination with alcohol to remove both ionic and non polar
                  compounds.

                  I used a three step cleaning process. After cleaning with all ordinary PCB
                  cleaning techniques I did a high presser wash with DI water to remove the polar
                  contaminates. Then I chased the water with ultra pure isopropinal to suck out
                  any remaining water and remove the non polar contaminates. Finally an overnight
                  bake out at 108C. All handling was done with rubber gloves (no talc please) and
                  forbad assembly by assemblers who smoked tobacco.

                  The banding of smokers was the result of spectrographic research I discovered
                  showing fingerprints on disk wafers made by assemblers wearing rubber gloves.
                  Nothings is as good as you think it is when you go for ultraclean.

                  My procedures resulted in a successful process but I was not dealing with high
                  temp or even high voltage. BTW my assembly department was not very happy with me
                  and would shortcut my "silly" procedures at every opportunity.

                  Fred Townsend

                  > I
                  > don't seem to be able to get rid of all of it.
                  >
                  > > BTW do you bake your PCBs after you wash them?
                  > >
                  > > Fred Townsend
                  > >
                  > >
                  > > "Syd Levine (AnaLog)" wrote:
                  > >
                  > > > I discoverd my problem, I think. I have been trying to use grocery
                  > store
                  > > > (Wal-Mart) distilled water to wash these dern PCBs. At 150C, the ionic
                  > > > residue is causing trouble. Where can I find good DI water in bottles?
                  > I
                  > > > hate to invest in a machine when I need maybe a gallon or two per week.
                  > I
                  > > > suspect I need water that is close to the chip making standards (18
                  > > > megohm/cm).
                  > > >
                  > > > Syd H. Levine
                  > > > AnaLog Services, Inc.
                  > > > Phone: 270-276-5671
                  > > > Telefax: 270-276-5588
                  > > > E-mail: analog@...
                  > > > URL: www.logwell.com
                  > > >
                  > > > --
                  > > > Author: Syd Levine \(AnaLog\)
                  > > > INET: AnaLog@...
                  > > >
                  > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
                  > > > San Diego, California -- Mailing list and web hosting services
                  > > > ---------------------------------------------------------------------
                  > > > To REMOVE yourself from this mailing list, send an E-Mail message
                  > > > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
                  > > > the message BODY, include a line containing: UNSUB CHIPDIR-L
                  > > > (or the name of mailing list you want to be removed from). You may
                  > > > also send the HELP command for other information (like subscribing).
                  > >
                  > >
                  > > --
                  > > Author: Fred Townsend
                  > > INET: fred@...
                  > >
                  > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
                  > > San Diego, California -- Mailing list and web hosting services
                  > > ---------------------------------------------------------------------
                  > > To REMOVE yourself from this mailing list, send an E-Mail message
                  > > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
                  > > the message BODY, include a line containing: UNSUB CHIPDIR-L
                  > > (or the name of mailing list you want to be removed from). You may
                  > > also send the HELP command for other information (like subscribing).
                  > >
                  >
                  > --
                  > Author: Syd Levine \(AnaLog\)
                  > INET: AnaLog@...
                  >
                  > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
                  > San Diego, California -- Mailing list and web hosting services
                  > ---------------------------------------------------------------------
                  > To REMOVE yourself from this mailing list, send an E-Mail message
                  > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
                  > the message BODY, include a line containing: UNSUB CHIPDIR-L
                  > (or the name of mailing list you want to be removed from). You may
                  > also send the HELP command for other information (like subscribing).


                  --
                  Author: Fred Townsend
                  INET: fred@...

                  Fat City Network Services -- 858-538-5051 http://www.fatcity.com
                  San Diego, California -- Mailing list and web hosting services
                  ---------------------------------------------------------------------
                  To REMOVE yourself from this mailing list, send an E-Mail message
                  to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
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                  also send the HELP command for other information (like subscribing).
                • Syd Levine (AnaLog)
                  We are testing prototypes with garden variety 140C FR4 from PCBexpress. Production models will be high temp 175C or 200C FR4. Polyimide (polyamide is nylon, I
                  Message 8 of 10 , Mar 2, 2003
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                    We are testing prototypes with garden variety 140C FR4 from PCBexpress.
                    Production models will be high temp 175C or 200C FR4. Polyimide (polyamide
                    is nylon, I think) has been the standard in my industry for a couple of
                    decades, but I hate the stuff. It is especially bad about absorbing
                    moisture and contamination.

                    Performance of the present PCB is ENTIRELY related to cleaning. In fact
                    performance improves after prolonged "cooking" in the test oven. The PCB I
                    am testing now has turned a pretty brown color (actually looks like
                    polyimide), but is working great. So whatever decomposition products are
                    being generated sure are not hurting things. The well browned PCBs may
                    actually perform better than the new ones.

                    Boiling the PCB in DI water is one technique I an using at present. Just
                    letting the PCB soak for a few hours in DI water after an ethanol (denatured
                    alcohol) scrub to remove flux residue works almost as well as the boiling
                    procedure. What I am struggling with now is the best standardized cleaning
                    procedure.

                    Of course, I do not know how much cleaning the production PCBs will require,
                    but I suspect some prior to potting.

                    ----- Original Message -----
                    To: "Multiple recipients of list CHIPDIR-L" <CHIPDIR-L@...>
                    Sent: Sunday, March 02, 2003 12:23 PM


                    > Syd, I think you raise a number of issues. My studies way back in the
                    early
                    > 1970s showed FR4 started out gassing and changing composition at 130C.
                    Some of
                    > the breakdown products were very acidic. Perhaps this is a decomposition
                    issue
                    > rather than an ionic contamination issue. Are you using high temperature
                    > laminates or ordinary FR4?
                    >
                    > BTW much later studies in the late 90s showed that polyamide boards were
                    > slightly lower in leakage at room temperature but considerably better at
                    high
                    > temperatures. I don't recall at how high a temperature I tested.
                    >
                    > "Syd Levine (AnaLog)" wrote:
                    >
                    > > These are getting baked after washing as part of the testing routine.
                    These
                    > > boards have to be able to go to 150C, and really need to go to 175C.
                    Would
                    > > soaking them in the distilled water help get the ionic residue off em.
                    >
                    > I'm inclined to believe that long term soaking is not a good idea. Most
                    > contaminates go into solution quickly so soaking is probably not
                    necessary. A
                    > lot would have to do with the quality of plated through holes (PTH) in the
                    PCB.
                    > If the holes are rough the plating may have voids or fissures that could
                    trap
                    > contaminates in the glass fiber within the PCB. When the board is heated
                    these
                    > fissures will spread the contamination back on the board surface.
                    >
                    > There is another issue. Ions conduct but so do metals and carbon, silicon
                    etc.
                    > Do you know for sure you have an ionic contamination issue?
                    >
                    > Still another issue. DI water is free of ions but not necessarily free of
                    > organic compounds. Distilled water is free from both ions and organic
                    material
                    > but very quickly turns acidic when exposed to air due to CO2 absorption.
                    I used
                    > DI water in combination with alcohol to remove both ionic and non polar
                    > compounds.
                    >
                    > I used a three step cleaning process. After cleaning with all ordinary
                    PCB
                    > cleaning techniques I did a high presser wash with DI water to remove the
                    polar
                    > contaminates. Then I chased the water with ultra pure isopropinal to suck
                    out
                    > any remaining water and remove the non polar contaminates. Finally an
                    overnight
                    > bake out at 108C. All handling was done with rubber gloves (no talc
                    please) and
                    > forbad assembly by assemblers who smoked tobacco.
                    >
                    > The banding of smokers was the result of spectrographic research I
                    discovered
                    > showing fingerprints on disk wafers made by assemblers wearing rubber
                    gloves.
                    > Nothings is as good as you think it is when you go for ultraclean.
                    >
                    > My procedures resulted in a successful process but I was not dealing with
                    high
                    > temp or even high voltage. BTW my assembly department was not very happy
                    with me
                    > and would shortcut my "silly" procedures at every opportunity.
                    >
                    > Fred Townsend
                    >
                    > > I
                    > > don't seem to be able to get rid of all of it.
                    > >
                    > > > BTW do you bake your PCBs after you wash them?
                    > > >
                    > > > Fred Townsend
                    > > >
                    > > >
                    > > > "Syd Levine (AnaLog)" wrote:
                    > > >
                    > > > > I discoverd my problem, I think. I have been trying to use grocery
                    > > store
                    > > > > (Wal-Mart) distilled water to wash these dern PCBs. At 150C, the
                    ionic
                    > > > > residue is causing trouble. Where can I find good DI water in
                    bottles?
                    > > I
                    > > > > hate to invest in a machine when I need maybe a gallon or two per
                    week.
                    > > I
                    > > > > suspect I need water that is close to the chip making standards (18
                    > > > > megohm/cm).
                    > > > >
                    > > > > Syd H. Levine
                    > > > > AnaLog Services, Inc.
                    > > > > Phone: 270-276-5671
                    > > > > Telefax: 270-276-5588
                    > > > > E-mail: analog@...
                    > > > > URL: www.logwell.com
                    > > > >
                    > > > > --
                    > > > > Author: Syd Levine \(AnaLog\)
                    > > > > INET: AnaLog@...
                    > > > >
                    > > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
                    > > > > San Diego, California -- Mailing list and web hosting
                    services
                    > > >
                    > ---------------------------------------------------------------------
                    > > > > To REMOVE yourself from this mailing list, send an E-Mail message
                    > > > > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
                    > > > > the message BODY, include a line containing: UNSUB CHIPDIR-L
                    > > > > (or the name of mailing list you want to be removed from). You may
                    > > > > also send the HELP command for other information (like subscribing).
                    > > >
                    > > >
                    > > > --
                    > > > Author: Fred Townsend
                    > > > INET: fred@...
                    > > >
                    > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
                    > > > San Diego, California -- Mailing list and web hosting services
                    > > > ---------------------------------------------------------------------
                    > > > To REMOVE yourself from this mailing list, send an E-Mail message
                    > > > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
                    > > > the message BODY, include a line containing: UNSUB CHIPDIR-L
                    > > > (or the name of mailing list you want to be removed from). You may
                    > > > also send the HELP command for other information (like subscribing).
                    > > >
                    > >
                    > > --
                    > > Author: Syd Levine \(AnaLog\)
                    > > INET: AnaLog@...
                    > >
                    > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
                    > > San Diego, California -- Mailing list and web hosting services
                    > > ---------------------------------------------------------------------
                    > > To REMOVE yourself from this mailing list, send an E-Mail message
                    > > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
                    > > the message BODY, include a line containing: UNSUB CHIPDIR-L
                    > > (or the name of mailing list you want to be removed from). You may
                    > > also send the HELP command for other information (like subscribing).
                    >
                    >
                    > --
                    > Author: Fred Townsend
                    > INET: fred@...
                    >
                    > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
                    > San Diego, California -- Mailing list and web hosting services
                    > ---------------------------------------------------------------------
                    > To REMOVE yourself from this mailing list, send an E-Mail message
                    > to: ListGuru@... (note EXACT spelling of 'ListGuru') and in
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                    > (or the name of mailing list you want to be removed from). You may
                    > also send the HELP command for other information (like subscribing).
                    >
                    >


                    --
                    Author: Syd Levine \(AnaLog\)
                    INET: AnaLog@...

                    Fat City Network Services -- 858-538-5051 http://www.fatcity.com
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                  • Fred Townsend
                    ... No polyamide is NOT nylon. Perhaps you mean kapton. Kevelar is the stuff bullet proof vests are made of. Both are polyamides. You can cut nylon with a
                    Message 9 of 10 , Mar 2, 2003
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                      "Syd Levine (AnaLog)" wrote:

                      > We are testing prototypes with garden variety 140C FR4 from PCBexpress.
                      > Production models will be high temp 175C or 200C FR4. Polyimide (polyamide
                      > is nylon, I think) has been the standard in my industry for a couple of
                      > decades, but I hate the stuff. It is especially bad about absorbing
                      > moisture and contamination.

                      No polyamide is NOT nylon. Perhaps you mean kapton. Kevelar is the stuff bullet
                      proof vests are made of. Both are polyamides. You can cut nylon with a soldering
                      iron but not a polyamide.

                      >
                      >
                      > Performance of the present PCB is ENTIRELY related to cleaning.

                      In turn your performance is entirely related to your soldering process and your
                      flux in particular. Several companies I have worked for employed a seven stage
                      inline washer. The first stage was ammonia. That was to neutralize the acid
                      flux. The last stage was DI water. Problems with analog boards dropped to
                      practically zero after the washer was installed.

                      Fred Townsend

                      > In fact
                      > performance improves after prolonged "cooking" in the test oven. The PCB I
                      > am testing now has turned a pretty brown color (actually looks like
                      > polyimide), but is working great. So whatever decomposition products are
                      > being generated sure are not hurting things. The well browned PCBs may
                      > actually perform better than the new ones.
                      >
                      > Boiling the PCB in DI water is one technique I an using at present. Just
                      > letting the PCB soak for a few hours in DI water after an ethanol (denatured
                      > alcohol) scrub to remove flux residue works almost as well as the boiling
                      > procedure. What I am struggling with now is the best standardized cleaning
                      > procedure.
                      >
                      > Of course, I do not know how much cleaning the production PCBs will require,
                      > but I suspect some prior to potting.
                      >
                      > ----- Original Message -----
                      > To: "Multiple recipients of list CHIPDIR-L" <CHIPDIR-L@...>
                      > Sent: Sunday, March 02, 2003 12:23 PM
                      >
                      > > Syd, I think you raise a number of issues. My studies way back in the
                      > early
                      > > 1970s showed FR4 started out gassing and changing composition at 130C.
                      > Some of
                      > > the breakdown products were very acidic. Perhaps this is a decomposition
                      > issue
                      > > rather than an ionic contamination issue. Are you using high temperature
                      > > laminates or ordinary FR4?
                      > >
                      > > BTW much later studies in the late 90s showed that polyamide boards were
                      > > slightly lower in leakage at room temperature but considerably better at
                      > high
                      > > temperatures. I don't recall at how high a temperature I tested.
                      > >
                      > > "Syd Levine (AnaLog)" wrote:
                      > >
                      > > > These are getting baked after washing as part of the testing routine.
                      > These
                      > > > boards have to be able to go to 150C, and really need to go to 175C.
                      > Would
                      > > > soaking them in the distilled water help get the ionic residue off em.
                      > >
                      > > I'm inclined to believe that long term soaking is not a good idea. Most
                      > > contaminates go into solution quickly so soaking is probably not
                      > necessary. A
                      > > lot would have to do with the quality of plated through holes (PTH) in the
                      > PCB.
                      > > If the holes are rough the plating may have voids or fissures that could
                      > trap
                      > > contaminates in the glass fiber within the PCB. When the board is heated
                      > these
                      > > fissures will spread the contamination back on the board surface.
                      > >
                      > > There is another issue. Ions conduct but so do metals and carbon, silicon
                      > etc.
                      > > Do you know for sure you have an ionic contamination issue?
                      > >
                      > > Still another issue. DI water is free of ions but not necessarily free of
                      > > organic compounds. Distilled water is free from both ions and organic
                      > material
                      > > but very quickly turns acidic when exposed to air due to CO2 absorption.
                      > I used
                      > > DI water in combination with alcohol to remove both ionic and non polar
                      > > compounds.
                      > >
                      > > I used a three step cleaning process. After cleaning with all ordinary
                      > PCB
                      > > cleaning techniques I did a high presser wash with DI water to remove the
                      > polar
                      > > contaminates. Then I chased the water with ultra pure isopropinal to suck
                      > out
                      > > any remaining water and remove the non polar contaminates. Finally an
                      > overnight
                      > > bake out at 108C. All handling was done with rubber gloves (no talc
                      > please) and
                      > > forbad assembly by assemblers who smoked tobacco.
                      > >
                      > > The banding of smokers was the result of spectrographic research I
                      > discovered
                      > > showing fingerprints on disk wafers made by assemblers wearing rubber
                      > gloves.
                      > > Nothings is as good as you think it is when you go for ultraclean.
                      > >
                      > > My procedures resulted in a successful process but I was not dealing with
                      > high
                      > > temp or even high voltage. BTW my assembly department was not very happy
                      > with me
                      > > and would shortcut my "silly" procedures at every opportunity.
                      > >
                      > > Fred Townsend
                      > >
                      > > > I
                      > > > don't seem to be able to get rid of all of it.
                      > > >
                      > > > > BTW do you bake your PCBs after you wash them?
                      > > > >
                      > > > > Fred Townsend
                      > > > >
                      > > > >
                      > > > > "Syd Levine (AnaLog)" wrote:
                      > > > >
                      > > > > > I discoverd my problem, I think. I have been trying to use grocery
                      > > > store
                      > > > > > (Wal-Mart) distilled water to wash these dern PCBs. At 150C, the
                      > ionic
                      > > > > > residue is causing trouble. Where can I find good DI water in
                      > bottles?
                      > > > I
                      > > > > > hate to invest in a machine when I need maybe a gallon or two per
                      > week.
                      > > > I
                      > > > > > suspect I need water that is close to the chip making standards (18
                      > > > > > megohm/cm).
                      > > > > >
                      > > > > > Syd H. Levine
                      > > > > > AnaLog Services, Inc.
                      > > > > > Phone: 270-276-5671
                      > > > > > Telefax: 270-276-5588
                      > > > > > E-mail: analog@...
                      > > > > > URL: www.logwell.com
                      > > > > >
                      > > > > > --
                      > > > > > Author: Syd Levine \(AnaLog\)
                      > > > > > INET: AnaLog@...
                      > > > > >
                      > > > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
                      > > > > > San Diego, California -- Mailing list and web hosting
                      > services
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                      > > > > > also send the HELP command for other information (like subscribing).
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                      > > > >
                      > > > > --
                      > > > > Author: Fred Townsend
                      > > > > INET: fred@...
                      > > > >
                      > > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
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                      > > >
                      > > > --
                      > > > Author: Syd Levine \(AnaLog\)
                      > > > INET: AnaLog@...
                      > > >
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                      > >
                      > > --
                      > > Author: Fred Townsend
                      > > INET: fred@...
                      > >
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                      > >
                      >
                      > --
                      > Author: Syd Levine \(AnaLog\)
                      > INET: AnaLog@...
                      >
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                      --
                      Author: Fred Townsend
                      INET: fred@...

                      Fat City Network Services -- 858-538-5051 http://www.fatcity.com
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                    • Syd Levine (AnaLog)
                      You have your polys mixed up. Polyamide IS nylon. Polyimide is kapton and the stuff use to make those high temp brown circuit boards. Two very different
                      Message 10 of 10 , Mar 3, 2003
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                        You have your "polys" mixed up. Polyamide IS nylon. Polyimide is kapton
                        and the stuff use to make those high temp brown circuit boards. Two very
                        different materials, spelled almost alike.

                        > No polyamide is NOT nylon. Perhaps you mean kapton. Kevelar is the stuff
                        bullet
                        > proof vests are made of. Both are polyamides. You can cut nylon with a
                        soldering
                        > iron but not a polyamide.


                        --
                        Author: Syd Levine \(AnaLog\)
                        INET: AnaLog@...

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