BGA's are killing my project

Hi everybody-

My project uses several BGA parts.  We're in the second board rev stage
(rev 2).  Our board manufacturer doesn't seem to be able to 100%
reliably solder those parts down.  It makes SW debugging troublesome
because one never knows if the SW or the part is misbehaving.  We've
had 15 boards built and I estimate 20% have BGA problems.

I'd like to hear other's experiences with and solutions to BGA
soldering reliability problems.  I have a few questions to kick off the
discussion:

Is it a manufacturer process problem that can be totally fixed with
some soldering process improvement? (Corollar: Is my board builder not
up to the task?)

Is this a natural and expected problem that I just have to live with
(result = reduced board yield)?

How much does the lead-free directive contribute to the problem? (My
rev 2 boards we're built using no-lead solder but rev 1 boards were
built using leaded solder and had the same BGA problems.)

Does X-ray inspection *really* identify badly soldered parts 100% of
the time?

What is a typical delivered board BGA solder failure rate that you guys
will accept?

Thanks for sharing your opinions and experiences.

JJS

johnspeth@yahoo.com wrote:
> Hi everybody-
>
> My project uses several BGA parts.  We're in the second board rev stage
> (rev 2).  Our board manufacturer doesn't seem to be able to 100%
> reliably solder those parts down.  It makes SW debugging troublesome
> because one never knows if the SW or the part is misbehaving.  We've
> had 15 boards built and I estimate 20% have BGA problems.
>
> I'd like to hear other's experiences with and solutions to BGA
> soldering reliability problems.  I have a few questions to kick off the
> discussion:
>
> Is it a manufacturer process problem that can be totally fixed with
> some soldering process improvement? (Corollar: Is my board builder not
> up to the task?)

It's a testing and QC/QA issue.

>
> Is this a natural and expected problem that I just have to live with
> (result = reduced board yield)?

No. you have to help the board assembler to solve the problem.

>
> How much does the lead-free directive contribute to the problem? (My
> rev 2 boards we're built using no-lead solder but rev 1 boards were
> built using leaded solder and had the same BGA problems.)

Yes, it does.  Lead-free requires higher temperature and more expensive
solder (silver).

>
> Does X-ray inspection *really* identify badly soldered parts 100% of
> the time?

Yes, it should help, together with boundary scans.  Are they Jtag
scanable?

>
> What is a typical delivered board BGA solder failure rate that you guys
> will accept?

Zero, they should go back to be oven.

> 
> Thanks for sharing your opinions and experiences.
> 
> JJS

johnspeth@yahoo.com wrote:

> Hi everybody-
> 
> My project uses several BGA parts.  We're in the second board rev stage
> (rev 2).  Our board manufacturer doesn't seem to be able to 100%
> reliably solder those parts down.  It makes SW debugging troublesome
> because one never knows if the SW or the part is misbehaving.  We've
> had 15 boards built and I estimate 20% have BGA problems.
> 
> I'd like to hear other's experiences with and solutions to BGA
> soldering reliability problems.  I have a few questions to kick off the
> discussion:
> 
> Is it a manufacturer process problem that can be totally fixed with
> some soldering process improvement? (Corollar: Is my board builder not
> up to the task?)

Possibly.  It may be a board layout problem, as well.  Assuming good 
layout then yes, the soldering process can be improved.

I'd make sure to get together with the chip vendor to make sure that you 
(or your layout people) understand the layout requirements and are 
adhering to them, then I'd start pounding on the board house.
> 
> Is this a natural and expected problem that I just have to live with
> (result = reduced board yield)?

No.
> 
> How much does the lead-free directive contribute to the problem? (My
> rev 2 boards we're built using no-lead solder but rev 1 boards were
> built using leaded solder and had the same BGA problems.)

I don't know, but from what I understand about lead-free processes your 
biggest two hurdles will be getting it tuned right to begin with, and 
tin whiskers down the road.  If your assembly house can't even do it 
with leaded solder that's not the problem.
> 
> Does X-ray inspection *really* identify badly soldered parts 100% of
> the time?

No.  X-ray inspection just looks down through the joint -- if there's 
solder there that's not sticking it can be very difficult to tell from a 
good joint.

It does make a difference, however, so it's not to be ignored.
> 
> What is a typical delivered board BGA solder failure rate that you guys
> will accept?

I stand around with my hands in my pockets laughing at folks who 
actually have to worry about this stuff, so I don't know.  But I _do_ 
know that we've used them in an environment where a 2% or 5% reject rate 
for the whole board would be considered "way bad", so you can bet we're 
seeing much less than that for BGA parts.

If I remember I'll check and let you know this evening.

I think you need to find an assembly house who has some mileage with BGA 
parts, or you need to see your current assembly house start some serious 
discussions with your chip vendor.  BGA parts have been around for 
nearly 10 years now, and they're becoming ubiquitous.  Any assembly 
house worth its salt really should know how to do it.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:

> > What is a typical delivered board BGA solder failure rate that you guys
> > will accept?
>
> I stand around with my hands in my pockets laughing at folks who
> actually have to worry about this stuff, so I don't know.  But I _do_
> know that we've used them in an environment where a 2% or 5% reject rate
> for the whole board would be considered "way bad", so you can bet we're
> seeing much less than that for BGA parts.

Well, that's for production, right?

Most of the assembly houses that do tiny runs for proto purposes
request a 10% overage on special parts (including BGAs) and yield is
often not guaranteed. Protos are often hand-assembled.

johnspeth@yahoo.com wrote:

> My project uses several BGA parts.  We're in the second board rev stage
> (rev 2).  Our board manufacturer doesn't seem to be able to 100%
> reliably solder those parts down.  It makes SW debugging troublesome
> because one never knows if the SW or the part is misbehaving.  We've
> had 15 boards built and I estimate 20% have BGA problems.

BGA solder problems can also be related to the PCB design. Make sure
your pads have the recommended size and shape. Vias in the pad, or very
near the pad can also cause problems by wicking the solder away from
the pad and into the hole.

Arlet wrote:
> johnspeth@yahoo.com wrote:
> 
> 
>>My project uses several BGA parts.  We're in the second board rev stage
>>(rev 2).  Our board manufacturer doesn't seem to be able to 100%
>>reliably solder those parts down.  It makes SW debugging troublesome
>>because one never knows if the SW or the part is misbehaving.  We've
>>had 15 boards built and I estimate 20% have BGA problems.
> 
> 
> BGA solder problems can also be related to the PCB design. Make sure
> your pads have the recommended size and shape. Vias in the pad, or very
> near the pad can also cause problems by wicking the solder away from
> the pad and into the hole.
> 
A specific piece of board design that will _kill_ you in BGAs is the 
pad. You really _must_ use non Solder Mask Defined pads if you want high 
yield (and I define that as 100% - I don't accept failures due to failed 
soldering).

I once worked at a company that had soldermask defined pads under a 
pretty large (768 balls) BGA, and the yield was horrendous. Went to 
non-SMD and the yields went way up.

I would be very surprised, assuming the layout is properly done and the 
CM has edxperience with BGAs, to _ever_ see a BGA failure rate higher 
than that for TQFP for soldering issues. BGAs are _easier_ on the process.

Cheers

PeteS

PeteS wrote:

> Arlet wrote:
> 
>> johnspeth@yahoo.com wrote:
>>
>>
>>> My project uses several BGA parts.  We're in the second board rev stage
>>> (rev 2).  Our board manufacturer doesn't seem to be able to 100%
>>> reliably solder those parts down.  It makes SW debugging troublesome
>>> because one never knows if the SW or the part is misbehaving.  We've
>>> had 15 boards built and I estimate 20% have BGA problems.
>>
>>
>>
>> BGA solder problems can also be related to the PCB design. Make sure
>> your pads have the recommended size and shape. Vias in the pad, or very
>> near the pad can also cause problems by wicking the solder away from
>> the pad and into the hole.
>>
> A specific piece of board design that will _kill_ you in BGAs is the 
> pad. You really _must_ use non Solder Mask Defined pads if you want high 
> yield (and I define that as 100% - I don't accept failures due to failed 
> soldering).
> 
> I once worked at a company that had soldermask defined pads under a 
> pretty large (768 balls) BGA, and the yield was horrendous. Went to 
> non-SMD and the yields went way up.
> 
> I would be very surprised, assuming the layout is properly done and the 
> CM has edxperience with BGAs, to _ever_ see a BGA failure rate higher 
> than that for TQFP for soldering issues. BGAs are _easier_ on the process.

Could you explain the difference?

Lead soldering of BGA's has been an almost zero defect process for our vendor. (< 0.1% error)

Switching to no-lead has caused some yield issues early on, but thay 
seem to have straightend them selves out.

It seems that the No-lead soldering has a lower margin for error.
Board must be properly designed, properly plated, and clean.


Paul




On 13 Oct 2006 08:38:17 -0700, johnspeth@yahoo.com wrote:

>Hi everybody-
>
>My project uses several BGA parts.  We're in the second board rev stage
>(rev 2).  Our board manufacturer doesn't seem to be able to 100%
>reliably solder those parts down.  It makes SW debugging troublesome
>because one never knows if the SW or the part is misbehaving.  We've
>had 15 boards built and I estimate 20% have BGA problems.
>
>I'd like to hear other's experiences with and solutions to BGA
>soldering reliability problems.  I have a few questions to kick off the
>discussion:
>
>Is it a manufacturer process problem that can be totally fixed with
>some soldering process improvement? (Corollar: Is my board builder not
>up to the task?)
>
>Is this a natural and expected problem that I just have to live with
>(result = reduced board yield)?
>
>How much does the lead-free directive contribute to the problem? (My
>rev 2 boards we're built using no-lead solder but rev 1 boards were
>built using leaded solder and had the same BGA problems.)
>
>Does X-ray inspection *really* identify badly soldered parts 100% of
>the time?
>
>What is a typical delivered board BGA solder failure rate that you guys
>will accept?
>
>Thanks for sharing your opinions and experiences.
>
>JJS

The main problem we are having with BGAs are the houses that do not have the 
technique down yet to mount them correctly. It has been a hell of a problem.

Phil


<johnspeth@yahoo.com> wrote in message 
news:1160753897.641258.18450@k70g2000cwa.googlegroups.com...
> Hi everybody-
>
> My project uses several BGA parts.  We're in the second board rev stage
> (rev 2).  Our board manufacturer doesn't seem to be able to 100%
> reliably solder those parts down.  It makes SW debugging troublesome
> because one never knows if the SW or the part is misbehaving.  We've
> had 15 boards built and I estimate 20% have BGA problems.
>
> I'd like to hear other's experiences with and solutions to BGA
> soldering reliability problems.  I have a few questions to kick off the
> discussion:
>
> Is it a manufacturer process problem that can be totally fixed with
> some soldering process improvement? (Corollar: Is my board builder not
> up to the task?)
>
> Is this a natural and expected problem that I just have to live with
> (result = reduced board yield)?
>
> How much does the lead-free directive contribute to the problem? (My
> rev 2 boards we're built using no-lead solder but rev 1 boards were
> built using leaded solder and had the same BGA problems.)
>
> Does X-ray inspection *really* identify badly soldered parts 100% of
> the time?
>
> What is a typical delivered board BGA solder failure rate that you guys
> will accept?
>
> Thanks for sharing your opinions and experiences.
>
> JJS
> 

PS..  The fab houses are having a hell of a problem with the lead free 
requirements and BGA problems for us have included that issue.


"Elan Magavi" <Elan@nomailnospam.com> wrote in message 
news:hkRXg.13781$e66.8826@newssvr13.news.prodigy.com...
> The main problem we are having with BGAs are the houses that do not have 
> the technique down yet to mount them correctly. It has been a hell of a 
> problem.
>
> Phil
>
>
> <johnspeth@yahoo.com> wrote in message 
> news:1160753897.641258.18450@k70g2000cwa.googlegroups.com...
>> Hi everybody-
>>
>> My project uses several BGA parts.  We're in the second board rev stage
>> (rev 2).  Our board manufacturer doesn't seem to be able to 100%
>> reliably solder those parts down.  It makes SW debugging troublesome
>> because one never knows if the SW or the part is misbehaving.  We've
>> had 15 boards built and I estimate 20% have BGA problems.
>>
>> I'd like to hear other's experiences with and solutions to BGA
>> soldering reliability problems.  I have a few questions to kick off the
>> discussion:
>>
>> Is it a manufacturer process problem that can be totally fixed with
>> some soldering process improvement? (Corollar: Is my board builder not
>> up to the task?)
>>
>> Is this a natural and expected problem that I just have to live with
>> (result = reduced board yield)?
>>
>> How much does the lead-free directive contribute to the problem? (My
>> rev 2 boards we're built using no-lead solder but rev 1 boards were
>> built using leaded solder and had the same BGA problems.)
>>
>> Does X-ray inspection *really* identify badly soldered parts 100% of
>> the time?
>>
>> What is a typical delivered board BGA solder failure rate that you guys
>> will accept?
>>
>> Thanks for sharing your opinions and experiences.
>>
>> JJS
>>
>
>