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