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April 2008

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Subject:
From:
Scott Westheimer <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Scott Westheimer <[log in to unmask]>
Date:
Tue, 22 Apr 2008 14:08:42 -0400
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Ryan,
 
Circumferential voiding normally is caused by air entrapment in the hole during metallization, after drilling. High surface tension of the solution along with poor solution movement and high surface energy of the hole wall entraps the air during processing and causes non-plating or limited plating at the center of the hole. Normally small holes 0.013 and less. Scott B. Westheimer5709 Clarks Fork DriveRaleigh, NC [log in to unmask]: (919)713-0748Cell NC: (919)961-5364Cell IL: (630)267-9655> Date: Tue, 22 Apr 2008 11:42:46 -0600> From: [log in to unmask]> Subject: [TN] Via barrel cracks> To: [log in to unmask]> > Hi Technetters,> > I have a case of via barrel cracks (E crack) and I would like to know> possible causes. > > The crack is circumferential and occurs at the center of the via. The> hole appears smooth, i.e., no glass nodules or tearout and there is> neither positive nor negative etchback. Of course there is some> wicking, but only about 25um max. The copper thickness is 20um at the> crack and roughly 35-40um at the knee. Although, at the initiation> point of the crack, the copper thickness is only 10um, but that could be> due to stretching and subsequent thinning of the copper. Around the> periphery of the crack are micro-voids in the resin about 30um. It is> triangular shaped, so I can't tell if it is resin recession or a> laminate crack. > > In other words, this via pretty much looks normal, except for one thing,> which might be an artifact of stretching and cracking of the via. For a> span of about 60um on the vertical of the via, at the crack, there is a> roughness that slightly reduces the copper thickness. The surface of> the copper at this point appears both rough and black in color.> > This board has seen two reflows and a hot functional test before final> failure.> > The board shop's initial response was speculation of the OSP soft etch> attacking the copper, but this particular via has solder mask plugging> both sides of the via; therefore chemicals after solder mask cure can> not get into the via.> > In case it matters, at one time, we have had occurrences of this board> shop "re-working" panels after copper plating by placing the panel in a> tank of etchant, then re-running the board through copper plating.> (They do panel plating).> > I'm a little suspicious of their FA, so I would like some independent> opinions and places for me to dig into.> > Thanks for any help,> Ryan> > ---------------------------------------------------> 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 847-615-7100 ext.2815> -----------------------------------------------------
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