Ring? Is it Pink ring? If I am right,pink ring around the holes is caused by the chemical solvent. I it probably that the chemical solvent went into the dielectric by the holes/vias.In order to solve this problem, you should bake the board after desmear process. 


======= 2002-03-26 15:48:00 您在来信中写道：=======

>Probably the following message did not get delivered to this forum a few
>days before since I did not get ANY reply hence posting it again.
>
>Hi Technetters,
>
>We are currently running an 8 layer PCB, 1.6mm thickness. In the last run of
>approx. 400 nos. we found approx. 10 nos PCBs with blisters in some specific
>areas. In approx. 40-50 nos. the blistering is not there but the laminate
>has discoloration.  More specifically, the blistering is seen in a
>particular area with a ground plane just beneath. In some PCBs the
>blistering is there on both sides of the PCB (just mirrored on both sides)
>and in some cases just on one side.
>
>Looking carefully at the bare PCBs I observed that there is a small ring
>around all the vias/PTHs with a width of approx. 0.2-0.3mm. This ring is
>basically the laminate itself but slightly raised and hence looking like a
>small ring. Is this normal? Can this be causing the blistering? OR is this
>an indication of some other phenomenon which is causing the blistering?
>Actually this ring is visible in ALL vias and PTHs all over the board, but
>blistering is happening ONLY in one particular area. What bothers me the
>most is that  ALL PCBs have this ring around the vias/PTHs but the
>blistering has happened in approx. only 10 out of 400 PCBs.
>
>Somebody pointed it out to the reflow profile, which actually is withing the
>the paste manufacturer's specified range. Even if it IS due to the profile
>then why ONLY 10/400? Why not more?
>
>Can anybody suggest any possible causes of the same.
>
>We are not baking the PCBs prior to processing, but the boards are in vacuum
>packing with 10 PCBs per bag and the packing is opened only at the Stencil
>printing stage.
>
>Any suggestions welcome.
>
>Regards
>Vinit Verma
>Flextronics Technologies (India) Pvt. Ltd.
>88A, Electronic City, Hosur Road,
>Bangalore-561 229
>Tel: +91-80-852 0022, Ext. 161 ; Fax: +91-80-852-1022
>E-Mail : [log in to unmask]
>
>---------------------------------------------------------------------------------
>Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
>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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL
>To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
>Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
>Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
>information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
>---------------------------------------------------------------------------------

= = = = = = = = = = = = = = = = = = = =
			

                    致
礼！
				 
               kevinyeah
               [log in to unmask]
					2002-03-28