RE: BGA Assembly

["John Haddy" <john.haddy@radiata.com>]

Anthony:

I'd try contacting the trade association covering contract
assemblers in the UK: SMART group http://www.smartgroup.org



Dimiter:

What I can tell you is that there should be no need for any
form of limiting feet, etc. The surface tension of solder
balls on BGAs is sufficient to provide self centreing during
reflow.

Your problem (below) sounds very much like a lack of flux.

BGAs can be assembled either with or without solder paste, which
is helpful in a prototyping environment, since you don't need to
get paste masks made. If you go the latter route, it is vital
that both the BGA balls and the PCB lands are covered with a
smear of flux paste (use a fairly stiff ~10mm paint brush),
taking care that only a smear is applied (too much and the BGA
will float off the lands during reflow.

I've hand assembled microBGA packages (233 pad, 0.8mm pitch)
without problems using a hot air rework station.

Cheers,

John Haddy

> -----Original Message-----
> From: Dimiter Popoff [mailto:tgi_earth@yahoo.com]
> Sent: Friday, 24 November 2000 1:58 PM
> To: pci-sig@znyx.com
> Subject: Re: BGA Assembly
> 
> 
> Anthony Moulds,
> 
> >Does anyone in the UK know of a company that can successfully
> >handle the assembly of fine-pitch BGA devices (FBGA680) in small
> >volumes? So far I've drawn a blank!
> 
> Well I am not in the UK but right now I am struggling with my first
> board which has 3 normal pitch (1.27) BGAs. The mistake I made
> with the first soldering attempt was that I fixed the chips to
> the board by glueing their corners to the board (using UV-hardening
> glue); the result was that the solder balls did never
> touch the pads, surface tension was > gravity impact.
> I removed the glue and put just limiting feet at each corner (I used
> pieces of enammeled wire); then back into the oven again.
> This time it worked - though, as I discovered later, I still had
> several non-contact pads ( I am still chasing one of them, one
> of the 3 BGA chips still does not work OK).
> Fortunately, I had routed the board with a hole (drilled 0.3mm)
> at each pad; repairing the bad ones turned out possible (but not easy,
> as one would expect). It amounted to a very hot soldering iron
> and a piece of 0.15mm copper wire (taken from a coax cable shield);
> with a drop of solder I could eventually melt all through the hole
> and reach to the the BGA ball. The wire was necessary to punch
> through the surface tension barrier, just solder did not always work.
> 
> Now while this is not the address of a company which would do
> small quantities for you I hope it may be useful during your
> prototyping. Good luck!
> 
> Dimiter
> 
> -----------------------------------------------------------------------
> Dimiter Popoff
> Transgalactic Instruments, Gourko Str. 25 b, 1000 Sofia, Bulgaria
> http://transgalactic.freeyellow.com
> Email: tgi@bulnet.bg, tgi_earth@yahoo.com
> Phone: 00359/2/9923340, 00359/2/9805997, Fax: 00359/2/9540384
> 
>