Need help...0.5mm pitch BGA pad removed

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Miib

Joined: 19 Nov 2004
Posts: 16

01 Jun 2005 8:29 Need help...0.5mm pitch BGA pad removed

Hi guys...i need your advise,

Currently i had working with a 0.5mm pitch BGA, because some of those BGA pads are not used, i plan to remove those pad in over to place a trace under it? will it cause any solder join problems after SMT process? have anyone face this kind of issue before?

Please give my some advise...Thanks

hock

Joined: 28 May 2001
Posts: 1291
Helped: 23
Location: India

01 Jun 2005 10:38 Re: Need help...0.5mm pitch BGA pad removed

how will you prevent the unused pins from getting soldred to your new tracks?

hock

Miib

Joined: 19 Nov 2004
Posts: 16

01 Jun 2005 11:56 Re: Need help...0.5mm pitch BGA pad removed

i plan to remove those pads and cover with soldermask, that's mean trace will go under the soldermask and it will not have contect with the BGA solder ball, what i affair is when doing the reflow in the SMT, those BGA pin/solder ball (which no pads under it) may cause solder join for other solder ball.

Did any one out there have this kind of concern before? please advise me...Thanks.

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havi

Joined: 25 Jun 2004
Posts: 62
Helped: 2

03 Jun 2005 8:51 Re: Need help...0.5mm pitch BGA pad removed

hai
there is no way. so you keep the pads as usual. and you can take tracks with pth (means removable pads pth area).

ezpcb

Joined: 02 Mar 2005
Posts: 202
Helped: 5

03 Jun 2005 9:18 Re: Need help...0.5mm pitch BGA pad removed

working on CSR chip? 0.5mm pitch is really difficult to deal with. you have to drag 4 mil tracks and very small holes. I think there should be OK to remove some pads, but the balls at the position of the removed pads MUSTalso be removed.

I'm not sure about my words, just my personal opnion. We have never done it in real work. if have difficult in maufacturing that board I can help.

Miib

Joined: 19 Nov 2004
Posts: 16

07 Jun 2005 2:49 Re: Need help...0.5mm pitch BGA pad removed

Thanks for the replys..... Ya...currently i deal with CSR chipset which is 0.5mm pitch, remove some pad are possible...but remove some ball on the CSR chip.... i not think so....(have to customize the chip), so...i think remove the BGA pad not a good ideal...

What will be the recommended via size/via hole between 0.5mm pitch? and what will be the cheapest solution on pcb stackup build?(such as using blind via, stacker via, skip via etc...)Need advise...

ezpcb

Joined: 02 Mar 2005
Posts: 202
Helped: 5

07 Jun 2005 3:15 Re: Need help...0.5mm pitch BGA pad removed

Hi Miib,

Actually I don't suggest you remove any pad or ball, that's not reliable for the fine pitch chips.

I suggest you use 6 layer, 4mil track/space and 0.15mm hole vias for CSR chip. Non of the blind vias, stack vias or skip vias are cheap. usually the price of such boards are 2-3 times than normal. but skip vias seems to be the most expensive. You can send me the design when you finish, I'll check for the manufacturablity for you.

mike

hooman

Joined: 25 Apr 2004
Posts: 20

13 Jun 2005 9:38 Re: Need help...0.5mm pitch BGA pad removed

I had worked with 1 and 1.27 pitches and I suggest you not to do that , beacuse of the high tempreture while mounting, it may cause short circiut in the board, the way is you use the pads for all but do not fanout the unused ones it, gives you the ability to use the inner layers there but not the top one,
I wish it help you.

Miib

Joined: 19 Nov 2004
Posts: 16

09 Jul 2005 3:16 Re: Need help...0.5mm pitch BGA pad removed

Thanks guys...

pvskt

Joined: 25 Jun 2005
Posts: 44
Helped: 6

12 Jul 2005 3:26 Re: Need help...0.5mm pitch BGA pad removed

I have worked on 0.5mm pitch BGAs on my wireless boards.

You can remove the pads which are unused freely without any concern. But, check with your assembly house whether they have experience in assembling 0.5mm BGAs. I was able to get my boards manufactured and assembled without any major problems.

Another option is, use via on the pad, if you feel that you are risking by removing the un-used pads. One more thing is, if you do not remove the unused pads, how will you be able to fan out the BGA or take the traces out unless and until the number of layers on the pCB are greater than oe equal to 8 or 10.