Jan,
To add a little more information to Steve's, even with proper layout of the
stencil you can experience "solder beads" or as listed "squeeze balls" form
any paste that is moved from the soldering surface, pad or termination. The
material that is not in contact with the main body of paste gets squeezed
out onto the board, flex or solder mask, and during reflow moves to wherever
there is the most heat. They can move under chips and caps or along the
edges.
VBK
Vincent B. Kinol CQE [log in to unmask] <mailto:[log in to unmask]>
Applications Engineer OMG Americas Microbond
Phone 919-544-8090 x298 FAX 919-544-7996
-----Original Message-----
From: Stephen R. Gregory [SMTP:[log in to unmask]]
Sent: Wednesday, January 19, 2000 11:15 AM
To: [log in to unmask]
Subject: Re: [TN] Reflow soldering >>> Solder balls
In a message dated 01/19/2000 9:55:42 AM Central Standard Time,
[log in to unmask] writes:
<< Ok..so what are the causes of solder beads?? >>
Hi Jan!
Solder beads or "Squeeze balls" as they're sometimes referred to,
are caused by too much of the gray stuff...solder paste. In a cleaning
environment they're usually not a problem because they wash off. But in a
no-clean environment, BIG headache!
They can be eliminated by modifying the apertures in your stencil to
reduce the volume of paste you're putting down. Instead of square apertures
you can turn them into triangles or "home-plates" with the pointy ends
pointing towards each other to the center of the footprint. A lot of
stencil vendors will do this automatically...at least mine does. I just tell
them I want no-clean apertures for all the passives...I think it's an extra
$25-50 charge for the editing they have to do in the gerber.
Hope this helps...
-Steve Gregory-
-----Original Message-----
From: Jan Satterfield [SMTP:[log in to unmask]]
Sent: Wednesday, January 19, 2000 10:31 AM
To: [log in to unmask]
Subject: Re: [TN] Reflow soldering >>> Solder balls
Ok..so what are the causes of solder beads??
> -----Original Message-----
> From: Kinol, Vince [SMTP:[log in to unmask]]
> Sent: Wednesday, January 19, 2000 6:17 AM
> To: [log in to unmask]
> Subject: Re: [TN] Reflow soldering >>> Solder balls
>
> Jens,
> I believe the TechNet archives will have some detail on solder
balls. In
> general there are a few causes for the formation of solder balls.
> Environmental exposure of the paste to moisture, this can be from
high
> humidity, extended queue times after printing or exposure of below
room
> temperature paste to room temperature air. (ie paste is below dew
point)
> Another cause would be oxidation of the solder alloy. This may
exist in
> the
> paste or be formed during the reflow process, due to the profile
not being
> optimized to the flux.
> Also just a note solder balls are very small and should not be
confused
> with
> solder beads, large coalesced solder found at times at edges of
caps and
> resistors.
> Feel free to contact me off line for more details.
> VBK
> Vincent B. Kinol CQE [log in to unmask]
<mailto:[log in to unmask]>
> Applications Engineer OMG Americas Microbond
> Phone 919-544-8090 x298 FAX 919-544-7996
>
>
> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Tuesday, January 18, 2000 11:16 PM
> To: [log in to unmask]
> Subject: [TN] Reflow soldering >>> Solder balls
>
> Hi,
>
> sorry for this basic basic question!
> Are there any resources for the solder balls problem?
Where do the
> come from and how to prevent them?
> Is there any site for solder defects info ?
> regards
> Jens Behrens
>
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