John,
        We print paste for all balled BGAs, for component retention and
additional solder volume. Using glue is tricky at best, if it cures and
solidifies it will prevent the component balls from collapsing during
reflow and possibly cause opens or marginal wetting. We only go without
paste during some rework operations where we use 'tacky flux' at the
repair site. There are a variety of references available from both
component and stencil manufacturers to assist you in selecting proper
aperture sizes for the component being processed.

        For profiling, you're best off taking a fully populated and
reflowed board for proper thermal loading. Drill and place the finest
gauge thermocouples you can find into the reflowed balls at the
perimeter and center of device, along with your standard SMT component
attachments.

Mike McMonagle
PCA Process Engineering Supervisor
K*Tec Electronics
1111 Gillingham Lane
Sugar Land, TX  77478
(281) 243-5639 Phone
(281) 243-5539 Fax
[log in to unmask]

> -----Original Message-----
> From: John Chandler [SMTP:[log in to unmask]]
> Sent: Wednesday, January 13, 1999 8:50 AM
> To:   [log in to unmask]
> Subject:      [TN] BGA and profiling
>
> We are getting into doing BGA's. Just a 27 by 27 overall dimension
> component, with pitch of 1.27 with 20 rows & columns, with balls. Not
> a
> complex part by any means. Our IC placement machine picks up,
> recognizes
> and places great. Been told that since the part is spec'ed out to be
> with
> balls, that it is either a hand place deal with a special machine or
> use
> glue dots on the masking of the PCB, to hold the component in place
> during
> reflow. No solder paste using a screen printer required.
>
> My questions are does anyone use solder paste and a screen to place
> BGA's
> with or without balls?   Where should the thermocouples be placed to
> get
> the proper reflow profile?
>
> Thanks in advanced.
>
> John Chandler
> ITRON
> 2818 N. Sullivan Road
> P.O. Box 15288
> Spokane, WA 99215
> [log in to unmask]
> Voice (509) 891-3343
>  Fax   (509) 891-3355
>
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