TECHNET Archives

June 2008

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Mon, 16 Jun 2008 11:46:44 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (109 lines)
Hi, Steve
I wanted to clear up a common assumption, very common but not always
true.

Preheating SMT chip caps and resistors to 130-150 deg. C. and immersing
them in 500 deg. F (260 C) molten solder for (typically) 2-3 seconds in
the wave solder process is not always worse than subjecting them to
convection reflow temperatures (especially those where the MRT is above
225 C for more than 30 seconds) for a full 7-8 minutes or longer. I have
had more instances where the convection reflow process induced or
contributed to reliability issues more often than I have with wave
solder.
There have been several times where I saw component fallout on parts
that were convection-reflow soldered, whereas the same part never failed
when wave-soldered on other assemblies.

With a small contribution to the Doug Pauls Mountain Dew Fund, it
depends on the components and the circuit board type.

But I do agree with your statement that a good selective wave fixture
that protects the part is usually the best option.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, June 16, 2008 10:05 AM
To: [log in to unmask]
Subject: Re: [TN] Glue Mask Requirements

Hi Natasha!

Most of the time, I just leave it up to my stencil vendor to create my
epoxy stencils for me when I have to use them. They do that from the
solder paste layer. 

Personally, I try to avoid using epoxy whenever I can, I just do a
double-sided reflow if there is SMT components on both sides of the
board. If I need to wave the board and the volume justifies it, I'll get
a selective wave solder fixture made which will mask off the SMT on the
bottom of the board. If it's a low volume board, and depending on the
amount of PTH components there are, I'll just have the PTH
hand-soldered.

A few reasons I don't like using glue are:

- It's messy
- There always seems to be handling issues with the boards after the
parts are epoxied on.
- It can't be too good on SMT parts being immersed in a 500-degree wave

Steve 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Natasha Baker
Sent: Monday, June 16, 2008 8:25 AM
To: [log in to unmask]
Subject: [TN] Glue Mask Requirements

Hi All,

I have a question regarding the glue mask when designing PCBs.

I am ordering the IPC SM-817 which provides requirements for surface
mounting adhesives, but am unsure if it will provide requirements
specifically on dimensions for the glue mask.  Are there concrete rules
for glue mask dimensions?  Or, should the glue mask just follow the
component outline?  Also, is it always necessary to use a glue mask, or
only when components are placed on both sides of the board?

Best Regards,

Natasha

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2