To Larry When the viscosity of the paste is to high then you will have all the problems listed in #2. The only thing we can do is increase the pressure or through it all out and try another tube however the next tube was no better. From John G -------------- Original message -------------- From: Larry Dzaugis <[log in to unmask]> > Two diffferent criteria. > 1. How repeatably is the PBC located to the stencil? > Mechanical locating stops? > Camera locating fiducials on PCB and stencil? > This is your off pad printing capability > The product and paste dictates what the % off pad can be. > > 2. The volume of paste deposited PCB to PCB and over time? > Does the stencil release the paste? > Is the opening filled with paste? > Do the blades scoop paste out? > Do they drag excess paste over the aperatures? > Some of the things that can happen during a run. > The volume tolerance is determined by the product, materials and > process. > > The other question becomes how is the paste measured, will it pass a gage R > and R? > Location much easier than volume. > Once there are numbers to what you can do, what can your process tolerate > ;and meet the requirements? > > All of these processes become "it depends" (Trademark Pending, used w/o > permission) on what the customer needs and what is willing to be risked by > you and your customer. > > > > On 11/24/08, Bob Willis wrote: > > > > It's a fair comment but you have to set your own standard to be able to set > > any automated process? > > > > If a standard is required IPC, SMTA and Automated Learning offers a photo > > CDs that has lots of print defects and reference prints. There are also > > some > > reference standards for printing. > > > > I have recommended in the past that IPC have criteria for printing and > > adhesive deposits to make the us of the DPMO documents and data collection > > easier to use. > > > > Many thanks > > > > Bob Willis > > 2 Fourth Ave, Chelmsford, Essex, CM1 4HA England > > Tel: (44) 1245 351502 > > Fax: (44) 1245 496123 > > Mobile: 07860 775858 > > > > www.ASKbobwillis.com > > New Bob Willis "Printed Board Inspection & Quality Control Workshop" 24th > > March www.ASKbobwillis.com/faworkshops.pdf > > > > "Troubleshooting Your Assembly Yields Workshop" 25th March > > www.ASKbobwillis.com/faworkshops.pdf > > > > Book Bob's "Step by Step Failure Analysis Workshop" 22nd April > > www.ASKbobwillis.com/faworkshops.pdf > > > > -----Original Message----- > > From: TechNet [mailto:[log in to unmask]] On Behalf Of Andy Ng > > Sent: 24 November 2008 03:41 > > To: [log in to unmask] > > Subject: Re: [TN] Screen printing > > > > There're no standards on misprinting as this is not a final > > workmanship/quality issue...rather a process issue...I'm sure > > engineers do set their own guidelines if you utilize an AOI or > > automated printing inspection system, depending on what type of > > component you're looking at...say, a 20-mil vs a 40-mil pitch QFP. But > > you're right, especially for high volume runs, controlling the > > printing can reduce a large portion of your defects and time lost. > > > > Andy > > > > Quoting John Goulet : > > > > > I've never heard of one. The IPC standard is for component > > > placement. Occassionally we may have the aperatures longer to print > > > off the pad on purpose to have more paste flow up the leads. > > > I put in a 1st peice inspection sheet for print, placement and the > > > paste used to assure at each changeover the process was good. This > > > prevents most of the misprints unless I get my finger in it during > > > inspection. Now that the operators know we are watching, the quality > > > has gone up substantially. If the camera gets out of calibration > > > then the prints can go off. The manaul printers are doing better and > > > stencil issues are caught much sooner before they cause a stop > > > process. > > > > > > > > > -------------- Original message -------------- > > > From: Yannick Brisson > > > > > >> Hi everyone!! > > >> > > >> Is anybody have a chart or rule or standard for misprint. What I mean is > > if > > >> there is a way of saying if my print for some reason a switch 1%, > > >> 5%, 10%, etc, > > >> off the pad that is not acceptable. > > >> > > >> Thank you > > >> Yannick > > >> > > >> --------------------------------------------------- > > >> Technet Mail List provided as a service by IPC using LISTSERV 15.0 > > >> To unsubscribe, send a message to [log in to unmask] with following text > > in > > >> the BODY (NOT the subject field): SIGNOFF Technet > > >> To temporarily halt or (re-start) delivery of Technet send e-mail to > > >> [log in to unmask]: SET Technet NOMAIL or (MAIL) > > >> To receive ONE mailing per day of all the posts: send e-mail to > > >> [log in to unmask]: SET Technet Digest > > >> Search the archives of previous posts at: > > http://listserv.ipc.org/archives > > >> Please visit IPC web site > > >> http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for > > >> additional information, or contact Keach Sasamori at [log in to unmask] or > > >> 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