Luo,
        I think that you have largely identified the main problem yourself. When I 
read your description below, you seem to be saying that on identical or nearly 
identical circuits, only the bottom side components tombstone. You also seem to 
indicate that the tombstoning occurs only after the second reflow when these 
components are reflowed while being on the bottom of the assembly. Simple solution 
would be to use some placement adhesive for the bottom side components suffering 
tombstoning during the second reflow operation.
        I am not a reflow soldering expert but I would have to believe that the small 
difference (3 mils) in your soldermask opening is only a minor contributor to the 
problem. Coupled with the direct plane connection this may add up to enough for the 
problem you are experiencing though.
        One detail that I don't believe you have mentioned clearly, is it the direct 
polygon connection component ends that are lifting or are those the ends which remain 
attached? Which end of the components is experiencing the problem (lifting) and what 
is unique about those ends in your design?
        Likewise if this soldermask opening turned out to be the issue and changing 
the soldermask opening fixes the problem then it is an easy fix that you could 
probably institute with a few design rules covering the oversizing of the soldermask 
openings for SMT bottom layer pads. (Never tried this but I would think you could 
write a rule to cover this instance and vary the opening for those effected pads. 
Might take several rules to clearly define the specific pad types that are effected.)
        Other issues that could help to see your problem more clearly, what are you 
pad geometries on these problem components. What is the pad size (X&Y) and the center 
to center distance between the pads? (I assume these are the 0402 parts as mentioned.) 
What are the dimensions of your solderpaste mask openings and the thickness of the 
paste deposition? Are the problem components resistors, capacitors or both (Note: caps 
are usually slightly thicker bodies (height) than resistors and could require a 
slightly longer (approx. 5 mils?) pad extension past the end of the device)? How 
accurate is the part placement? Are the components machine or manually placed (like 
they may do in China)?
        There are an awful lot of possibilities. I think that we are starting to get 
down to the details if you can answer all of the questions I posed, either just to 
your own satisfaction or shared with the rest of us.

Sincerely,
Brad Velander.

Lead PCB Designer
Norsat International Inc.
Microwave Products
Tel   (604) 292-9089 (direct line)
Fax  (604) 292-9010
email: [EMAIL PROTECTED]
http://www.norsat.com


> -----Original Message-----
> From: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED]
> Sent: Tuesday, March 04, 2003 7:54 PM
> To: Protel EDA Forum
> Subject: Re: [PEDA] Components tombstoning After reflow.
> 
> Subject: RE: [PEDA] Components tombstoning After reflow.
> 
> Dear Brad, Lan & others,
> 
> Thank you very much for yours kindly respond and instructions. 
> 
> Since the assembly house is in another city, I could not get the exact
> information about this issue, Please allow me to forward your 
> instructions
> to them to try and analyze. Meanwhile, they also mentioned 
> the soldmask open
> on the pads which connect to copper plane, I set the slodmask 
> override to
> 3mil on normal pads, So, according to my polygon connect 
> style, The actual
> pad size on the copper plane will be large than the design 
> size (3mil each
> side), Thus, a component with two different size pads, maybe 
> this will cause
> tombstoning after reflow, So I reduce the soldmask open size 
> as same as the
> pad size (override size = 0, just those pads connect to 
> copper plane). I
> wonder if this is helpful.
> 
> Currently, the component size is 0402, yes, we used to use 
> 0603 or large
> parts and no tombstoning occur. We found this issue most 
> recently, but we
> had changed the component size for a span seldom found 
> tomdstoning. I also
> notice two RF module samples, one with components on both 
> side, one with
> single side components, The bottom layout of the one with both side
> components is same as the the one with single side component, 
> After reflow,
> the single-side-component module no tombstoning , The 
> double-side-components
> module with many tombstoning on the bottom side (The top side 
> contains 4 BGA
> ICs, it is to say the bottom side components go through the 
> reflow twice. )
> , I will try to change my habit in next design, but I wonder 
> if the polygon
> connect style is really critical, and does anyone else have 
> got experiences
> on this?
> 
> Thanks again!
> 
> Best regards,
> Luo.
> 
> -----Original Message-----
> From: Brad Velander [mailto:[EMAIL PROTECTED]
> Sent: Tuesday, March 04, 2003 1:22 AM
> To: Protel EDA Forum
> Subject: Re: [PEDA] Components stand After reflow.
> 
> 
> Luo,
>       the problem you are experiencing is called 
> "tombstoning" in English.
> Tombstoning typically occurs because of incorrect component 
> pad geometries,
> solder volumes or reflow heat profiles. It can be effected by 
> your polygon
> connections but as you state it is not the only reason as not 
> all polygon
> connects do it and some components that are not connected to 
> polygons also
> do it.
>       The cause of tombstoning is varied but typically it 
> occurs because
> the viscosity of the molten solderpaste at one end of the component is
> greater than the viscosity of the molten solder paste at the 
> other end of
> the component or it has melted prior to the other end 
> melting. Sometimes
> this is because one end of the component reaches the solder melt point
> faster than the other end (which end hits the heat first?), 
> usually the end
> that is attached to the solderpad reached melting temperature 
> prior to the
> other end (the one stuck up in the air).
>       You will need to work with the assembly facility to 
> determine the
> cause of this tombstoning, there are many possible reasons 
> and they are not
> all board design related. One simple test, try putting the 
> boards through
> the reflow oven in a different orientation, 90 degrees clockwise or 90
> degrees counter-clockwise. There is a preferred orientation 
> for most boards,
> at least if they are properly laid out in the first place, not just
> willy-nilly on component orientation. The bias should see the 
> heat profile
> sweeping across both ends of chip components, down both sides of SOIC
> components simultaneously rather than one end and then the 
> other (one side
> and then the other for SOIC parts).
>       My money would be on the assembly line running a quick 
> temperature
> ramp-up, or they are just not adequately preheating before 
> the components
> hit the main reflow temperature phase. This is probably 
> resulting in the
> leading edge solder melting prior to the trailing edge solder 
> on small chip
> components. What size are your components, 0402 (or even 
> 0201)? Lots of
> people running 0603 or larger parts, then changing to 0402 or 
> 0201 have
> problems with tombstoning where they had no prior problems 
> with the larger
> parts. Do you have much history running these components through this
> assembly line?
> 
> Sincerely,
> Brad Velander.
> 
> Lead PCB Designer
> Norsat International Inc.
> Microwave Products
> Tel   (604) 292-9089 (direct line)
> Fax  (604) 292-9010
> email: [EMAIL PROTECTED]
> http://www.norsat.com
> 
> 
> > -----Original Message-----
> > From: [EMAIL PROTECTED] 
> > [mailto:[EMAIL PROTECTED]
> > Sent: Sunday, March 02, 2003 6:36 PM
> > To: Protel EDA Forum
> > Subject: [PEDA] Components stand After reflow.
> > Dear All,
> > 
> > I always set the polygon connect to pads directly, and it 
> > always work fine.
> > But now, we found there are components stand after reflow, 
> > some  contain
> > pads connect to polygon, some not. I wonder if this is caused 
> > by the polygon
> > connet style or any other reason. So my question is:
> > 
> > 1, what are the key points to cause components stand after reflow?
> > 2, When will components-stand always occur during reflow 
> > process? Preheat or
> > cool.
> > 3, How to slove this problem?
> > 
> > I am looking forward to your constructive suggestions, any 
> > input would be
> > great appreciated!
> > 
> > Best Regards,
> > Luo.
> 
> 
> ------_=_NextPart_001_01C2E2CA.E0DE9570
> Content-Type: text/html;
>       charset="big5"
> Content-Transfer-Encoding: quoted-printable
> 
> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
> <HTML>
> <HEAD>
> <META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; =
> charset=3Dbig5">
> <META NAME=3D"Generator" CONTENT=3D"MS Exchange Server version =
> 5.5.2653.12">
> <TITLE>RE: [PEDA] Components tombstoning After reflow.</TITLE>
> </HEAD>
> <BODY>
> 
> <P><FONT SIZE=3D2>Subject: RE: [PEDA] Components tombstoning After =
> reflow.</FONT>
> </P>
> <BR>
> 
> <P><FONT SIZE=3D2>Dear Brad, Lan &amp; others,</FONT>
> </P>
> 
> <P><FONT SIZE=3D2>Thank you very much for yours kindly respond and =
> instructions. </FONT>
> </P>
> 
> <P><FONT SIZE=3D2>Since the assembly house is in another 
> city, I could =
> not get the exact information about this issue, Please allow me to =
> forward your instructions to them to try and analyze. 
> Meanwhile, they =
> also mentioned the soldmask open on the pads which connect to copper =
> plane, I set the slodmask override to 3mil on normal pads, So, =
> according to my polygon connect style, The actual pad size on the =
> copper plane will be large than the design size (3mil each 
> side), Thus, =
> a component with two different size pads, maybe this will cause =
> tombstoning after reflow, So I reduce the soldmask open size 
> as same as =
> the pad size (override size =3D 0, just those pads connect to copper =
> plane). I wonder if this is helpful.</FONT></P>
> 
> <P><FONT SIZE=3D2>Currently, the component size is 0402, yes, 
> we used =
> to use 0603 or large parts and no tombstoning occur. We found this =
> issue most recently, but we had changed the component size 
> for a span =
> seldom found tomdstoning. I also notice two RF module 
> samples, one with =
> components on both side, one with single side components, The bottom =
> layout of the one with both side components is same as the 
> the one with =
> single side component, After reflow, the 
> single-side-component module =
> no tombstoning , The double-side-components module with many =
> tombstoning on the bottom side (The top side contains 4 BGA 
> ICs, it is =
> to say the bottom side components go through the reflow twice. ) , I =
> will try to change my habit in next design, but I wonder if 
> the polygon =
> connect style is really critical, and does anyone else have got =
> experiences on this?</FONT></P>
> 
> <P><FONT SIZE=3D2>Thanks again!</FONT>
> </P>
> 
> <P><FONT SIZE=3D2>Best regards,</FONT>
> <BR><FONT SIZE=3D2>Luo.</FONT>
> </P>
> 
> <P><FONT SIZE=3D2>-----Original Message-----</FONT>
> <BR><FONT SIZE=3D2>From: Brad Velander [<A =
> HREF=3D"mailto:[EMAIL PROTECTED]">mailto:[EMAIL PROTECTED]
> om</A>]</F=
> ONT>
> <BR><FONT SIZE=3D2>Sent: Tuesday, March 04, 2003 1:22 AM</FONT>
> <BR><FONT SIZE=3D2>To: Protel EDA Forum</FONT>
> <BR><FONT SIZE=3D2>Subject: Re: [PEDA] Components stand After =
> reflow.</FONT>
> </P>
> <BR>
> 
> <P><FONT SIZE=3D2>Luo,</FONT>
> <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <FONT SIZE=3D2>the =
> problem you are experiencing is called &quot;tombstoning&quot; in =
> English. Tombstoning typically occurs because of incorrect component =
> pad geometries, solder volumes or reflow heat profiles. It can be =
> effected by your polygon connections but as you state it is not the =
> only reason as not all polygon connects do it and some 
> components that =
> are not connected to polygons also do it.</FONT></P>
> 
> <P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <FONT 
> SIZE=3D2>The cause =
> of tombstoning is varied but typically it occurs because the 
> viscosity =
> of the molten solderpaste at one end of the component is 
> greater than =
> the viscosity of the molten solder paste at the other end of the =
> component or it has melted prior to the other end melting. Sometimes =
> this is because one end of the component reaches the solder 
> melt point =
> faster than the other end (which end hits the heat first?), 
> usually the =
> end that is attached to the solderpad reached melting 
> temperature prior =
> to the other end (the one stuck up in the air).</FONT></P>
> 
> <P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <FONT 
> SIZE=3D2>You will =
> need to work with the assembly facility to determine the 
> cause of this =
> tombstoning, there are many possible reasons and they are not 
> all board =
> design related. One simple test, try putting the boards through the =
> reflow oven in a different orientation, 90 degrees clockwise or 90 =
> degrees counter-clockwise. There is a preferred orientation for most =
> boards, at least if they are properly laid out in the first 
> place, not =
> just willy-nilly on component orientation. The bias should 
> see the heat =
> profile sweeping across both ends of chip components, down 
> both sides =
> of SOIC components simultaneously rather than one end and then the =
> other (one side and then the other for SOIC parts).</FONT></P>
> 
> <P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <FONT 
> SIZE=3D2>My money =
> would be on the assembly line running a quick temperature 
> ramp-up, or =
> they are just not adequately preheating before the components 
> hit the =
> main reflow temperature phase. This is probably resulting in the =
> leading edge solder melting prior to the trailing edge solder 
> on small =
> chip components. What size are your components, 0402 (or even 0201)? =
> Lots of people running 0603 or larger parts, then changing to 
> 0402 or =
> 0201 have problems with tombstoning where they had no prior problems =
> with the larger parts. Do you have much history running these =
> components through this assembly line?</FONT></P>
> 
> <P><FONT SIZE=3D2>Sincerely,</FONT>
> <BR><FONT SIZE=3D2>Brad Velander.</FONT>
> </P>
> 
> <P><FONT SIZE=3D2>Lead PCB Designer</FONT>
> <BR><FONT SIZE=3D2>Norsat International Inc.</FONT>
> <BR><FONT SIZE=3D2>Microwave Products</FONT>
> <BR><FONT SIZE=3D2>Tel&nbsp;&nbsp; (604) 292-9089 (direct line)</FONT>
> <BR><FONT SIZE=3D2>Fax&nbsp; (604) 292-9010</FONT>
> <BR><FONT SIZE=3D2>email: [EMAIL PROTECTED]</FONT>
> <BR><FONT SIZE=3D2><A HREF=3D"http://www.norsat.com"; =
> TARGET=3D"_blank">http://www.norsat.com</A></FONT>
> </P>
> <BR>
> 
> <P><FONT SIZE=3D2>&gt; -----Original Message-----</FONT>
> <BR><FONT SIZE=3D2>&gt; From: [EMAIL PROTECTED] </FONT>
> <BR><FONT SIZE=3D2>&gt; [<A =
> HREF=3D"mailto:[EMAIL PROTECTED]">mailto:Luo.Yu-Min
> [EMAIL PROTECTED]
> -inc.com</A>]</FONT>
> <BR><FONT SIZE=3D2>&gt; Sent: Sunday, March 02, 2003 6:36 PM</FONT>
> <BR><FONT SIZE=3D2>&gt; To: Protel EDA Forum</FONT>
> <BR><FONT SIZE=3D2>&gt; Subject: [PEDA] Components stand After =
> reflow.</FONT>
> <BR><FONT SIZE=3D2>&gt; Dear All,</FONT>
> <BR><FONT SIZE=3D2>&gt; </FONT>
> <BR><FONT SIZE=3D2>&gt; I always set the polygon connect to pads =
> directly, and it </FONT>
> <BR><FONT SIZE=3D2>&gt; always work fine.</FONT>
> <BR><FONT SIZE=3D2>&gt; But now, we found there are components stand =
> after reflow, </FONT>
> <BR><FONT SIZE=3D2>&gt; some&nbsp; contain</FONT>
> <BR><FONT SIZE=3D2>&gt; pads connect to polygon, some not. I 
> wonder if =
> this is caused </FONT>
> <BR><FONT SIZE=3D2>&gt; by the polygon</FONT>
> <BR><FONT SIZE=3D2>&gt; connet style or any other reason. So my =
> question is:</FONT>
> <BR><FONT SIZE=3D2>&gt; </FONT>
> <BR><FONT SIZE=3D2>&gt; 1, what are the key points to cause 
> components =
> stand after reflow?</FONT>
> <BR><FONT SIZE=3D2>&gt; 2, When will components-stand always occur =
> during reflow </FONT>
> <BR><FONT SIZE=3D2>&gt; process? Preheat or</FONT>
> <BR><FONT SIZE=3D2>&gt; cool.</FONT>
> <BR><FONT SIZE=3D2>&gt; 3, How to slove this problem?</FONT>
> <BR><FONT SIZE=3D2>&gt; </FONT>
> <BR><FONT SIZE=3D2>&gt; I am looking forward to your constructive =
> suggestions, any </FONT>
> <BR><FONT SIZE=3D2>&gt; input would be</FONT>
> <BR><FONT SIZE=3D2>&gt; great appreciated!</FONT>
> <BR><FONT SIZE=3D2>&gt; </FONT>
> <BR><FONT SIZE=3D2>&gt; Best Regards,</FONT>
> <BR><FONT SIZE=3D2>&gt; Luo.</FONT>
> </P>
> <BR>
> 
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