Hi, James.
Yes, you CAN safely solder MLCCCs using a solder iron, but it is dependent on operator training and operator diligence. For hand soldering a MLCCC, have them flux and apply solder to one pad first, then place the part, melt the solder on that first pad by touching the PAD ONLY with the iron. Then solder the other side by again touching the pad only with the iron while adding a little wire solder. For water-soluble process, use flux if necessary. For no-clean soldering, do not use a liquid flux, you should be able to solder with only the flux contained in the wire core.
However, my experience has shown they should be trained to never use a tweezer style or U-shaped tip to solder the part in, as this thermally shocks the MLCCC directly and has proven to be the single biggest cause of cracked chips in a hand-solder or rework process. They can use a tweezer or U-shaped tip style to remove a chip cap or resistor that will not be re-used, but let's be practical, if the tweezer style iron is available, they will use it to place the part, hold it down with a pick, and release. That's what operators do. So don't allow the use of the tweezer style on any chip cap or resistor. Many of the chip resistors are also ceramic and they are also susceptible to this as well. Rather than have the operator need to look at a BOM to discern which chip caps are ceramic and which ones are not, we train them to use the pad doming method I described above (IPC 7711 section 5.3.2) on all chip caps/resistors, i.e., treat them all as being ceramic.
The methods described in IPC 7711 sections 3.3.1, 3.3.2, and 3.3.3 work well for removal, BUT ARE NOT INTENDED FOR REPLACEMENT. For replacement, I actually prefer using the hand-held hot air wand whenever possible because I was properly trained (to be a trainer) by a Master IPC trainer, and Replacement methods using the hot air wand are shown in sections 5.3.1 (don't be confused by the error where they describe solder paste but show wire solder being deposited) and 5.3.2, which is the point-to-point method I describe, except they show direct contact with the tip, which is not necessary.
The method shown in 5.3.1 really works if you follow the steps exactly as shown. The chip does not blow away. The trick is learning to adjust the hot air wand air flow and the two-stage distance to first properly dry the solder paste, then move in to reflow it. When the solder paste becomes liquid (thanks Werner) it holds the chip securely, it never blows away.
But you probably came to the same conclusion that I have, in that there are many circuit boards that simply can't get hot enough to use the hot air wand. So the indirect iron method seems to work well from an all around standpoint.
I would sure like to hear from others on the forum on this subject.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of James Liddle
Sent: Wednesday, April 29, 2009 3:01 AM
To: [log in to unmask]
Subject: [TN] FW: Lead Free Reworking of Multilayer Ceramic Capacitors
Hello
When carrying out a rework or repair of a RoHS Compliant PWA, I have been using Lead Free Solder, Alloy Designation SAC 305, RS Stock Number 445-5858, for Hand Soldering operations. Given that Lead Free Solder has a higher melting point than Tin Lead Solder, the Manufacturer of this has suggested that temperature of the Soldering Tip used in conjunction with it, should be between 350°C and 370°C for effective results. However, with regards to Multilayer Ceramic Capacitors, this conflicts with the advice published on page 97 of AVX's Surface Mounting Guide, which recommends Hot Air Reflow as the preferred rework method; and to a lesser extent, section 3.3 of Yageo's MLCC Application Manual.
Given that in a lot of instances Hand Soldering is the only practical method, does anyone know of a technique where it can safely be employed for Multilayer Ceramic Capacitor rework, using Lead Free Solder?
Thanks
James Liddle
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