Head in pillow and Graping are closely related in origin, and cure. Possibly also - due to the interactive nature of everything in solder paste processing - you need to look at printing as well as flux behaviour. Powder size is not normally the limiting factor in fine pitch printing, but transfer efficiency. So as noted try and stay with larger size where ever possible to avoid increasing the possible oxide burden on the flux. Particle surface area increases geometrically as diameter decreases. Nitrogen can help in reducing flux damage at very fine pitch and therefore reduce this problem, but it is possible to resolve this problem without recourse to it. Regards Mike -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Cedric ORAIN Sent: Wednesday, April 21, 2010 9:12 PM To: [log in to unmask] Subject: Re: [TN] R: [TN] Head in Pillow and grapping effects mitigation without Nitrogen We still using type 4 that give good results with 110um (laser cut nickel stencil). -----Message d'origine----- De : TechNet [mailto:[log in to unmask]] De la part de Gabriele Sala Envoyé : mercredi 21 avril 2010 22:04 À : [log in to unmask] Objet : [TN] R: [TN] Head in Pillow and grapping effects mitigation without Nitrogen Hi Cedric, What are you using as powder size in your actual solder paste ? : - Type-4 ? - Type-5 ? For your application Type-4 could work, better if Type-5, but as you know as powder size gets smaller the risk of powder oxidation increases, so N2 could be a must during reflow. Gabriele -----Messaggio originale----- Da: TechNet [mailto:[log in to unmask]] Per conto di Cedric ORAIN Inviato: mercoledì 21 aprile 2010 21.55 A: [log in to unmask] Oggetto: Re: [TN] Head in Pillow and grapping effects mitigation without Nitrogen I wasn't thinking about warpage as HOP cause, I will take care of that :thanks. And no, I've never encountered grapping and HOP at the same time. The point is that it deals with 2 kinds of defects that are coming with miniaturization. -----Message d'origine----- De : TechNet [mailto:[log in to unmask]] De la part de Genny Gibbard Envoyé : mercredi 21 avril 2010 21:30 À : [log in to unmask] Objet : Re: [TN] Head in Pillow and grapping effects mitigation without Nitrogen At Apex, one of the primary causes reported for HOP was component warping. However, if you are also getting graping at the same time, then to me it appears that it is a solder quality/heat issue. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier Sent: April 21, 2010 1:05 PM To: [log in to unmask] Subject: Re: [TN] Head in Pillow and grapping effects mitigation without Nitrogen Hi Cedric, What do you mean by 'grapping effect"? You do not say where you find 'Head-on-Pillow' defects-they can occur at the BGA periphery and in the BGA center and the root cause is quite different. HOP at the periphery is a solderability issue and certainly involves the choice of paste/flux. HOP in the BGA center means you do not have enough heat there to get the solder ball to a low-viscosity liquid state-that means you need to increase the peak reflow temperature. One of the reasons for larger solder volumes is to achieve greater SJ stand-off heights to improve reliability. Werner -----Original Message----- From: Cedric ORAIN <[log in to unmask]> To: [log in to unmask] Sent: Wed, Apr 21, 2010 2:38 pm Subject: [TN] Head in Pillow and grapping effects mitigation without Nitrogen Hello all, Very fine pitch BGAs (typically 0.5mm) and 0201 chips are becoming common in our company for some months. We recently have to face with new defects type such as grapping effect and head in pillow defect. The solder paste we use has been qualified for even smaller component (WLP, 0.4mm pitch) but in Nitrogen atmosphere. I'm now wondering if this solder paste is suitable with Air reflow. I'm also wondering if a solder paste suitable in that case even exists. Having a look to this study from intel (link hereunder, page 31), I found that the people from Intel are recommending a solder paste volume larger than 2000 mil^3 as a minimum. http://edc.intel.com/Download.aspx?id=3044&returnurl=/default.aspx That is, off-course, impossible for a VFBGA (which solder paste deposit is closer to 900mil^3) but this reading makes me feel uncomfortable. So the question is: is it possible to find out a solder paste which is suitable for VFBGA assembly in Air reflow? If it is not against TechNet rules, have you some solder paste references that you could advise? Here are some additional details: ENIG PCB finition, SAC305 Alloy. Cedric ORAIN Technical Director Electronic Manufacturing Services www.inovelec-groupe.com PS: I'm very new and I'm also French. I wish it will not be too much for you! Anyway, thank for being patient if I have difficulties to understand. ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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