I would be quite worried at what I see here. To me, it looks like
vesication. This is caused by the solder mask being placed over a
hygroscopic contaminant. As the mask is semi-porous (as are all
polymers), the contaminant absorbs moisture and forms the bubble where
adhesion is poor. Note that there is a halo round each defect; this
could be because the pressure in the bubble rises and tends to pull the
mask off.
You can confirm this possible diagnosis by autoclaving a board in steam,
using a domestic pressure cooker for 24 h or so (making sure that it
never boils dry). If the problem appears worse, then it is confirmed.
Brian (not brain: I lost that many years ago!)
Luan Nguyen wrote:
> Sorry! I send you file attached but maybe you will not receive it. You
> can see the picture on
> http://picasaweb.google.com/johnynhluan/BubbleDefectOnPCB
>
> Best regards,
>
>
>>>> [log in to unmask] 10-Jan-08 08:32:31 >>>
> Thank you Brain!
> I have some pictures of this defect to refer.
> Please give me a advice for this defect.
>
> Thanks and best regards,
>
>
>>>> [log in to unmask] 09-Jan-08 13:37:58 >>>
> If there is one >0.25 mm, then the board should be rejected.
> If there are 3 or more of <0.25 mm the board should be rejected.
>
> Furthermore, and this is my opinion, if a bubble <0.25 mm is between
> two
> tracks and occupies >50% of the spacing between the tracks, it should
> also be rejected.
>
> Brian
>
> Luan Nguyen wrote:
>> Dear Technet,
>> Our company were been happening a problem on PCB, details:
>> Per IPC-A-600, Revision G
>> 2.9 SOLDER RESIST (Solder Mask)
>> 2.9.4 Blisters/ Delamination
>> - Acceptable - class 2,3:
>> . Two per side not exceeding 0.25 mm [0.00984 in] in the greatest
>> dimension.
>>
>> According to our understanding:
>> - If there are 3 bubbles and each of them is exceeding 0.25 mm in
> the
>> greatest dimension per side, this is defect.
>> - In case, if there are more than 3 bubbles and each of them is not
>> exceeding 0.25 mm in the greatest dimension per side, this is defect
> or
>> accept ???
>> Please help us understand clearly it.
>>
>> Thanks and best regards,
>>
>>
>> ***************************
>> Nguyen Hoang Luan
>> QC&Training Supervisor
>> Spartronics VietNam Co, Ltd.
>> No.3, Street No.6, VSIP
>> Th An Dist., BDuong Prov., VN
>> Tel: (84-650) 784 890
>> Fax: (84-650) 784 891
>> Mobile: 090.3.667448
>> Email: [log in to unmask]
>> ***************************
>>
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