TECHNET Archives

July 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:
Leif Erik Laerum <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Leif Erik Laerum <[log in to unmask]>
Date:
Thu, 31 Jul 2008 15:05:18 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (363 lines)
*****CORRECTION********

Interesting feedback.

The stencil is indeed 6 mil thick.

The resistor pack pads are 22 x 10 mil and have 20 mil pitch. The
smallest BGA pads are 13 mil and have 30 mil pitch.

Is it the case that type 5 has a higher flux percentage than the type 3.
If so that could explain some of our findings.

Leif Erik Laerum
Quality Assurance Manager
Texas Memory Systems
[log in to unmask]
Tel: (713) 266-3200 x468
www.texmemsys.com



Guy Ramsey wrote:
> Smallest pads under mm BGA + 6 (60 mil??)laser cut stencil + type 5 paste =
> me confused.
>
> This would be, in my opinion, a recipe for hot slump and solder fines. A
> design with components and features like you describe should be fine with
> type 3 paste. Let's talk about those capacitor and resistor networks. What
> is their pitch and land pattern dimension? Smaller than the BGA? A lot
> smaller? Okay maybe type 4 paste and a 4 or 5 mil stencil.
>
> Guy
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum
> Sent: Thursday, July 31, 2008 11:34 AM
> To: [log in to unmask]
> Subject: Re: [TN] Solder Paste with craters.
>
> Paul et al,
>
> The bubbles are more prevalent on the smallest apertures such as 1 mm BGA
> pads and the resistor/capacitor pack pads.
> The temperature in the production area is between 68F and 75F. Humidity is
> relatively steady at 40%. (We are in Houston....)
>
> If anyone has any suggestions how to test the screens for cleanliness that
> would be great. That is a part of our process we do not control. We have a
> stencil cleaner, but we can only visually see if they are really getting
> clean. We also bought some stencil cleaner for manually wiping down a
> screen, but it actually makes the screens "greasy". We stopped using it.
>
> Ours stencils are the standard 60 mil laser cut. We do use a metal squeegee.
>
>
>
>
>
> Leif Erik Laerum
> Quality Assurance Manager
> Texas Memory Systems
> [log in to unmask]
> Tel: (713) 266-3200 x468
> www.texmemsys.com
>
>
>
> Paul Edwards wrote:
>
>> Leif,
>>
>> I just have 2 questions...
>>
>> What size apertures do these bubbles occur on and is there a
>> particular aperture orientation in which they are prevalent?
>>
>> What is the humidity and temperature of the environment for the paste
>> prior to putting it on the stencil>>
>>
>> Have seen something similar in certain kinds of SAC W/S pastes that
>> have been exposed to too much moisture and certain stencil cleaning
>> compounds...The saponifier was making soap bubbles when rolling in the
>> paste...
>>
>> Paul
>> Paul Edwards
>> Surface Art Engineering
>>
>>
>>
>>
>>
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum
>> Sent: Wednesday, July 30, 2008 1:56 PM
>> To: [log in to unmask]
>> Subject: Re: [TN] Solder Paste with craters.
>>
>> Thank you everyone for contributing. Especially you, Richard.
>>
>> First of all these are NOT via in cap boards and we are using FR4.
>> Been there done that....
>>
>> Most of the items brought up by Richard we do have established
>> processes for. These are according to the recommendations of the
>> solder vendor, but if others feel differently, please chime in.
>> We log the solder used for each batch and the Date of Manufacture
>> for this. We typically do not accept a batch of solder that is older
>> than 3 mts. This is so that we do not end up with too much out of date
>> solder at the end.
>>
>> - Solder is brought out of the fridge minimum 12 hours before use.
>> - We set a time limit that solder must can be stored out of the fridge
>> a maximum of 3 mts. Practically this ends up around 1 month max.
>> - We do reuse solder that has been on the screen for up to two weeks.
>> Then we throw it out.
>> - We never put solder back in the fridge.
>> - We are evaluating new suppliers of solder at the moment. We have not
>> audited the currents supplier, but that is a good idea. We always get
>> the solder couriered locally and in a cool container so I do not have
>> any evidence that would lead me to put this on the solder vendor,
>> but.....
>> - As our process works boards sit no longer than 1 hour with solder.
>> Usually much shorter than that.
>> - We are using Type 5 solder actually.
>> - All misprints go though the wash before it is reprinted.
>> - We use a DEK 248 that is not as automatic as I would like and some
>> of the issues we see are due to this repeatability problem, but from
>> the data I have gathered, this is not the cause of the solder fines
>> and craters.
>> - A Solder AOI would be nice. We do not have one of these (yet???)
>> - There could be an issue with too much solder. We are going to reduce
>> apertures some. There is some evidence of excessive solder.
>> - I am going to experiment with slowing down the print separation speed.
>> Good point.
>>
>> Thx.
>>
>> Leif Erik Laerum
>> Quality Assurance Manager
>> Texas Memory Systems
>> [log in to unmask]
>> Tel: (713) 266-3200 x468
>> www.texmemsys.com <http://www.texmemsys.com>
>>
>>
>>
>> Inge wrote:
>>
>>> Hi Leif, you've just listened to His Master's Voice.
>>> You should take off your cap, when you speak to Richard Stadem.
>>> Impressive! I begin to feel that there are two exceptional stars at TN.
>>> Steve...we already knew
>>> Richard...a supernova
>>>
>>> Inge
>>>
>>> Gah...my example was not very clever...a supernova is bright just
>>> for a short time...hmmm...a red giant then? hmmm...or a white
>>> dwarf...hm...none of them very striking....hmm....shining like
>>> Betelgeuse...hmm.....maybe Master Whittaker can give a hand?
>>>
>>>
>>> ----- Original Message ----- From: "Stadem, Richard D."
>>> <[log in to unmask]>
>>> To: <[log in to unmask]>
>>> Sent: Wednesday, July 30, 2008 6:53 AM
>>> Subject: Re: [TN] Solder Paste with craters.
>>>
>>>
>>> Hi, Leif
>>> Send your pictures to [log in to unmask]
>>>
>>> Can you tell me what solder paste it is you are using? How was it
>>> qualified for use?
>>>
>>> Here are just some of the questions you need to ask yourself in
>>> order to determine why you have an issue with solder fines:
>>> Do you have a good documented solder paste handling procedure? How
>>> is the paste handled, from vendor or distributor to your factory?
>>> When was the last time you stopped in at the distributor to verify
>>> their stock is being rotated and is kept refrigerated immediately
>>> upon receipt from the factory? How often do they turn the packages
>>> upside down to prevent flux separation? Are they a certified
>>> distributor who will pass on to you a lot recall notice from your
>>> solder paste vendor if there is a known bad lot?
>>> How long is the paste allowed to sit out on the stencil and how many
>>> times can a line of paste on the stencil be sheared (printed back
>>> and
>>> forth) before it is removed and replenished with fresh paste? Are
>>> the operators allowed to scrape up the unused paste on the stencil
>>> and re-deposit it into a jar for re-use later? Is the jar or tube of
>>> solder paste, once removed from refrigeration, allowed to set for
>>> two to four hours (depending on paste vendor and paste type) to
>>> reach room temperature prior to printing? Once removed from the
>>> refrigerator, is unused solder paste allowed to be put back in the
>>> refrigerator? Are you using Type 4 paste or Type 3? How good is the
>>> printer setup, ie, the repeatability of the registration of the
>>> stencil to the PWB? Are you performing some type of aperture
>>> reduction on all pads in general and at least a 50% reduction on
>>> large belly pads to prevent solder fines from being printed onto the
>>> board? If a board is misprinted, does the operator know better than
>>> to simply wipe off the board (embedding the paste into every space
>>> between the edges of the pads and the soldermask, into every small
>>> via, into every through hole, etc.) but is there a documented
>>> procedure detailing how the misprinted board is to be cleaned to
>>> prevent this? How is the solder paste packaged, jar or tube? (Tubes
>>> prevent a much larger volume of paste from being exposed to air and
>>> humidity, and also help prevent re-use of solder paste that has been
>>> out for awhile). Do you perform a good solder paste print inspection
>>> using a 3d AOI or some other type of automated inspection, and do
>>> you use the data from this inspection process to detect (real-time)
>>>
> paste defect trends and react to them with corrective actions?
>
>>> Sorry to ask so many questions, but all of these can contribute to
>>> fines, and there are many more factors that can cause them.
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum
>>> Sent: Wednesday, July 30, 2008 8:29 AM
>>> To: [log in to unmask]
>>> Subject: [TN] Solder Paste with craters.
>>>
>>> Technetters,
>>>
>>> We are having an issue with solder fines on our lead free boards. We
>>> are using SAC305 WS and no nitrogen. I noticed that our boards have
>>> craters in the paste on the pads after being printed. Not all pads
>>> are deposited this way, but maybe 25%. These craters have an air
>>> bubble in them. The bubbles usually burst before the boards goes
>>> into the P&P, but the crater stays. The screening process is exactly
>>> the same for leaded and unleaded paste. The leaded paste does not
>>> behave this way. Could these craters be a symptom of the cause of
>>> the solder fines? Anyone have any experience with this?
>>>
>>> How do I go about posting pictures to stevezeva.homestead.com?.
>>>
>>>
>>> --
>>> Leif Erik Laerum
>>> Quality Assurance Manager
>>> Texas Memory Systems
>>> [log in to unmask]
>>> Tel: (713) 266-3200 x468
>>> www.texmemsys.com <http://www.texmemsys.com>
>>>
>>> ---------------------------------------------------
>>> 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
>>> -----------------------------------------------------
>>>
>> ---------------------------------------------------
>> 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
>> -----------------------------------------------------
>> ----------------------------------------------------------------------
>> --
>> **
>>
>> This email and any attachments thereto may contain private,
>> confidential, and privileged material for the sole use of the intended
>> recipient. Any review, copying, or distribution of this email (or any
>> attachments thereto) by others is strictly prohibited. If you are not
>> the intended recipient, please contact [log in to unmask]
>> <mailto:[log in to unmask]> immediately and permanently
>> delete the original and any copies of this email and any attachments
>> thereto.
>>
>> **
>>
>> *
>> ----------------------------------------------------------------------
>> --
>> *
>>
>
> ---------------------------------------------------
> 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