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Date: | 10 Jan 97 09:13:29 -0500 |
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Thad,
Circuits Assembly magazine featured this technique in its Sept. 1996
edition, in an article called "Advanced Surface-Mount Manufacturing
Methods". The article included a table of formulas for pad size and paste
volume. I know there are resources on the net as well; Amp has a
discussion of this technique at www.amp.com/product/articles/dd66.html.
When I worked with Motorola on 2 way radio products, we used this technique
on every product. The joint does differ greatly from wavesolder joints,
but it is still a robust joint and we did not see any significant ALT or
field issue if the design work was done right and the process is
controlled.
Another thing: there are a lot of solder preforms that will aid this
technique (preforms are put on the part before insert; this provides more
stable solder volumes compared to screening into the hole).
Chris Messner
United Technologies Electronic Controls
[log in to unmask]
219-358-3429
______________________________ Reply Separator _________________________________
Subject: ASSY: IR Reflow of Thru-Hole Components
Author: [log in to unmask] at internet
Date: 1/10/97 12:46 AM
Some questions for the Technet,
One of our PCA Assembly subcontractors uses IR Reflow to reflow
through hole parts instead of the traditional Wave. They typically
use this technique for high density double side SMT/Through hole
assemblies where there is no room for the keepouts necessary to mask
the SMT parts during the wave process.
The technique involves a double Paste screening operation to squeegee
paste into the through holes. The board is run through IR to reflow
both the SMT and the Thru Hole parts. The solder joints look
completely different than a typical wave reflowed thru-hole part. In
fact I think they would be considered rejectable per IPC-A-610B. The
solder joints look as follows (forgive the art, I hope this tranlates
well):
| |
___________ | | __________
| | | |
|* | | *|
|** | | **|
|****| |****|
|****| |****|
|****| |****|
|****| |****|
|****| |****|
|****| |****|
|****| |****|
|****| |****|
|****| |****|
|****| |****|
|****| |****|
|****| |****|
|** | | **|
|* | | *|
________| | | |___________
| |
| |
|______|
Where "*" is solder.
---------------------------------------
I have several questions for the forum and would greatly appreciate
feedback:
1. Is there an industry term for this type of reflow. I've heard
it referred to as "intrusive reflow". Since I love catchy names, I'm
soliciting one.
2. Is the technique in widespread practice in the industry or is
it new?
3. Any comments on the reliability of such a solder joint.
4. Do standards (IPC or otherwise) exist that describe a "good"
joint and a "bad" joint. I'm interested in IPC Class II product.
5. Are there any tricks of the trade in designing boards for this
type of assembly. For example do I need to use modified (i.e.
smaller) thermals on my through holes to insure good reflow.
6. Are there special processing techniques in assembly that will
produce good joints. Example - screening paste on both sides or using
special pastes.
7. How can these joints be non-destructively evaluated since they
can't be seen other than microsection. Do periodic destructive tests
need to be done per an AQL.
8. I'm aware that any through hole components that use this
technique must be made of high temperature material to withstand IR,
but are there any other restrictions regarding what type of components
this assembly technique can be used for.
I would appreciate any feedback or comments you might have on this.
Thanks,
[log in to unmask]
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