Phil, We haven't seen a real difference in solder adhesion with ENIGed PCAs whether they were baked or not.... However we use the 150-160F in-air bake to control moisture in and stabilize the PCAs we get from our customers. Because we have large prototyping customer base, we have found that the bake seems to minimize the PCB warp during reflow... I have used "vacuum bake" ovens for both vacuum bake (no inlet gas) and partial- pressure bake (inlet "bleed" gas) and the IR driven vacuum bake process works better and faster than the partial pressure process for reducing the moisture content of the PCB's internal laminate layers. Paul Paul Edwards Process Engineering [log in to unmask] Tel: 408-433-4700 FAX: 408-433-9988 Surface Art Engineering 81Bonaventura Dr. San Jose, CA 95134 DUNS: 944740570 CAGE/NCAGE: 1XZ48 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro Sent: Wednesday, August 31, 2005 8:00 PM To: [log in to unmask] Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability I think I know what this discussion is missing ....someone who isn't working to comment on it!...lol. Anyways, I think I know what may have gone wrong in Dave's experiment as my experiments yielded the opposite results. I certainly agree that baking is not going to improve the solderability on ENIG boards, but I have never been able to discern a difference if prebaked using this vacuum oven process. The vacuum oven was set at 150 F to minimize the oxidation back in the days of HASL boards and still helps on ENIG as the gold does not seal the nickel below 100%. This process is still being used by my former employer and survived numerous challenges by Quality Engineers who only believed in the 220 F/24 hrs prebake cycle. Vacuum ovens (at least all of mine) have three ports on them, the largest one being in back and is for the vacuum pump, and then two smaller ports with a hose bibs on them at the front, one for room air which releases the vacuum pressure, and the other one is for bleeding in dry nitrogen gas. The vacuum and the heat sets the water molecules in motion, but without a nitrogen gas stream flowing across the pwb surface, the water does not want to leave the PWB. Based on Bev's addition below, my assumption is that most of the moisture is removed by the mechanical flow effects of the gas being bled in and very little of it actually dissolves into the nitrogen. Important also is that the dry nitrogen gas is being flow limited and therefore trickled (bled) in to the vacuum oven chamber at a slower rate than the pump is pulling the atmosphere out. The pump is left on continuously and maintains at least 24 inches of vacuum. I started using this process many years ago for wavesoldering .125" thick PWBs which had stored in wet conditions and exhibited huge outgassing during wavesoldering unless vacuum baked like this. Recently, a particularly aggresive ENIG stackup design forced me to have to use it in order to keep extremely the high density microvia technology board from delaminating due to the spacing of the drilled holes and the properties of the laminates. Besides that, it also saves 22 hours when it comes to rebaking boards before reworking them. Hope this is clear enough for everyone to understand....... Phil Bev Christian <[log in to unmask]> wrote:Paul, There is a big diference in the scale of interest between a printed circuit board and the dimensions on a Si wafer. I am afraid you are going to have to prove to me with data that this could ever be an issue with a PCB. Bev RIM -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Paul Edwards Sent: August 31, 2005 1:43 PM To: [log in to unmask] Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability Bev, Both N2 and H20 exists as a gas molecules in the air.. In the presence of static charging sources they can be ionized and disassociated to form nitrogen compounds.. This can be easily seen in Si wafer cleaning processes prior to epi... Paul Paul Edwards Process Engineering [log in to unmask] Tel: 408-433-4700 FAX: 408-433-9988 Surface Art Engineering 81Bonaventura Dr. San Jose, CA 95134 DUNS: 944740570 CAGE/NCAGE: 1XZ48 -----Original Message----- From: Bev Christian [mailto:[log in to unmask]] Sent: Wednesday, August 31, 2005 10:30 AM To: TechNet E-Mail Forum; Paul Edwards Subject: RE: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability Paul, Please explain to me how in the world molecular nitrogen (N2) is going to react with water vapor in a benign environment like a near vacuum at less than 200C. I quote from the Webelements website http://www.webelements.com/webelements/elements/text/N/chem.html: "Reaction of nitrogen with air Nitrogen gas does not react with air under normal conditions. Reaction of nitrogen with water Nitrogen gas does not react with water. It does, however, dissolve to the extent of about x g kg-1 at 20°C (297 K) and 1 atmosphere pressure." We aren't not talking about lightning bolts of charge here. I would expect the amount of charge caused by static to be relatively small, BUT I can always be educated. :) Bev RIM -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Paul Edwards Sent: August 31, 2005 1:22 PM To: [log in to unmask] Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability Dave, In the vacuum baking environment, the vacuum is used to lower the partial pressure to 0 to increase the molecular diffusion of the water out of the laminate structure.. In your experiments, the gas(N2 or Ar), serves as a thermal transfer agent so gas filled baking would be more effective than the vacuum baking, if the thermal energy source were heating coils... If laminate absorbing IR sources were used instead, a vacuum bakeout would be more effective than a "dry" gas bakeout. Again assuming the thermal energy source is a heating coil, the ideal baking method would be to use "bone-dry" or -100F (1ppm) or better Ar, assuming that the moisture in the PCAs would not raise the moisture level within the total Ar load to 0F (800ppm)... I wouldn't use N2 because of molecular acid formation when the N2 reacts with H20 and static electric charging sources that could occur in high air flow environments... Paul Paul Edwards Process Engineering [log in to unmask] Tel: 408-433-4700 FAX: 408-433-9988 Surface Art Engineering 81Bonaventura Dr. San Jose, CA 95134 DUNS: 944740570 CAGE/NCAGE: 1XZ48 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman Sent: Wednesday, August 31, 2005 7:53 AM To: [log in to unmask] Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability Hi Bev! Exactly! And most folks who use a vacuum bake process just kick on the vacuum and away they go! They don't realize that the bake/vacuum recipe they have chosen might be impeding the removal of moisture. Dave Bev Christian OM> To Sent by: TechNet [log in to unmask] cc Subject 08/31/2005 09:48 Re: [TN] ENIG/ Immersion Gold AM Plating and Pre-baking & Solderability Please respond to TechNet E-Mail Forum ; Please respond to Bev Christian OM> The trick is to have the evaporation process (driving the concentration gradient) to be slow enough to not comsume all the heat available so that the water stays liquid. Bev RIM -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Vladimir Igoshev Sent: August 31, 2005 10:15 AM To: [log in to unmask] Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability Hi Dave, That is a nice example of an adiabatic process, but it's "slightly different" from "pumping" moisture out of a board. :-) I'm a bit surprised with the results of your experiments. I'd expect both process to complement each other and speed up the process: vacuuming - to maintain the concentration gradient (driving force) and heating - to speed up diffusion (and prevent moisture from "freezing" :-)). Regards, Vladimir Vladimir Igoshev, Ph. D. Senior Materials Researcher Research in Motion 451 Phillip St. Waterloo, ON, N2L 3X2 Voice: (+1) 519-888-7465, ext. 5283 Fax: (+1) 519-886-0863 E-mail: [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of David D. Hillman Sent: Tuesday, August 30, 2005 6:31 PM To: [log in to unmask] Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability Hi Richard! Just a word of caution - I did some experimenting a number of years ago to see if either baking or vacuum baking was more effective in removing moisture from a pwb. I expected that the vacuum baking would be the winner but the design of experiments results demonstrated that baking was more effective. The physical process of pulling a vacuum to remove water ends up playing with the change of state (liquid to gas, gas to liquid, etc) behavior which impacts the ability to remove water from the pwb. I did some research and found a need example of pulling a vacuum on a disk of water - the change of state from a liquid to a gas resulted in the formation of ice (not exactly the result anyone wants to achieve)! The research illustrated that with the right controls and a well characterized vacuum/heating recipe you can effectively remove moisture faster than just baking but in a practical sense, having a nitrogen or argon atmosphere with a typical baking process was just as effective and lower cost. Any moisture baking process is going to degrade the pwb solderability so avoiding baking if possible is the best option. Dave Hillman Rockwell Collins [log in to unmask] "Stadem, Richard" D-AIS.COM> To Sent by: TechNet [log in to unmask] cc Subject 08/30/2005 08:27 Re: [TN] ENIG/ Immersion Gold AM Plating and Pre-baking & Solderability Please respond to TechNet E-Mail Forum ; Please respond to "Stadem, Richard" D-AIS.COM> I do not know the answer to that, but it sounds like a good idea. I do know that back in the 70's a major military OEM used to regularly bake pwb's at 150 F (note F, not C) at a 1/2 gravity vacuum, and they claimed the moisture was not removed if they did not have the 1/2 gravity vacuum. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Creswick, Steven Sent: Tuesday, August 30, 2005 8:24 AM To: [log in to unmask] Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability Richard, Is it an approved/acceptable process to place the PWB's into a vacuum chamber at room temp? I would not hazard a guess as to how great of a vacuum for what duration, however. Just curious if it is done in the surface mount industry. Nothing gets any more simple than a dessicantor box though! Steve Creswick - Gentex Corp -----Original Message----- From: Stadem, Richard [mailto:[log in to unmask]] Sent: Tuesday, August 30, 2005 9:05 AM To: [log in to unmask] Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability Baking of ENIG plated boards may be a requirement in order to drive out moisture even though it can exacerbate a nickel oxide formation that is already started. But there are other options for moisture removal, including lower bake temperatures at longer times. You could even lease a precision scale and see at what length of time is required for simply putting the PWB into a drybox (a dessicator box such as McDry, not a nitrogen box) and allowing it to dry at room temperature for a period long enough to reduce the moisture content by 90% or more. J-STD-030 does state that the bake times and temperatures they list for components and pwbs are guidelines. If you can prove your bake process or dessication process is removing the moisture, then you are qualifying a lower temp and longer time. You will need to use a number of pwbs in order to do this, as there is some variation in weights caused by resin content, etc. But you should be able to show a reduction in the average of weights (mean weight). -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Schaefer Sent: Friday, August 26, 2005 10:10 AM To: [log in to unmask] Subject: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability Does baking these types of plating affect solderability? If so what factors play a part (i.e. baking temperature, plating thickness, baking time, etc...). I know that if baked it can cause the Nickel Oxide layer to become less solderable if the plating process is Poor (thanks Richard S.). Is there is a factual study that proves that baking any type of gold plated boards in any way shape or form reduces the solderability and/ or reliablity of the joints/ product? I am trying to gather data to prove to management that baking is a bad decision with this type of plating and should never be performed. Also if a Gold Plated board of any type is suspect for high level moisture content - how do you remove the moisture "IF" baking is not acceptable? 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