Howard,
We use .006" stencils and do not need to push the PLCC into the paste. This MAY help, and, a thicker stencil MAY
help, but, without knowing how bent lead is from the seating plane, it is difficult to assess how thick a stencil will
be needed. I suggest you send a sample of components to a 3rd party to measure these components on a piece of
equipment with a good vision system suitable for measuring coplanarity. Most Tape and Reel houses have these.
Systems such as an "August Technologies" is a table top system. ICOS is another system that will work. If you
do business with any Tape and Reel or Lead Reconditioning companies, they would be the best place to start to
see if they can offer you this service.
-Carrie
-----Original Message-----
From: Howard Watson [mailto:[log in to unmask]]
Sent: Tuesday, May 13, 2003 11:58 AM
To: Morse, Carrie
Cc: TechNet E-Mail Forum.
Subject: RE: [TN] Coplanarity of PLCC's
Carrie,
This is a tape & reel component, and I can't find any internal cause. The leads that don't solder are visibly bent inwards, but on a "J" lead, when it gets pushed inward, the amount of vertical lift is much less - it's like a pendulum. What I'm concerned about is if the coplanrity is close to the .004" spec, then the bent leads won't touch solder paste until all the leads are .004" or more into the paste. I'm not sure if that will work on this size component, with a .007" thick paste deposit. From that standpoint, using a thicker stencil to get taller paste deposits probably won't do anything if I can't get the component more into the paste. Is it normal to push a PLCC 68 more than half way into the paste?
Howard Watson
SMT Manufacturing Engineer
AMETEK/Dixson
"Morse, Carrie" <[log in to unmask]>
05/12/03 01:44 PM
To: "TechNet E-Mail Forum." <[log in to unmask]>, "Howard Watson" <[log in to unmask]>
cc:
Subject: RE: [TN] Coplanarity of PLCC's
Howard,
Are you sure that Moto is sure that the one corner that looks like it's bent is really within .004"?
If you can see a bent lead, it is more than .004"! If they measured it on the same piece of equipment
they measured it in the first place, there may be something wrong. Is it possible their equipment is wrong?
I'd hate to see you running around trying to develop a new process when in reality the input to your process
is not correct (ie: coplanarity of the comp.)
May I suggest that the next time you run into this problem you have a 3rd party measure the coplanarity.
That way you can have objective evidence to provide back to Moto.
Also, is it possible that you may be damaging that one lead when retrieving it from the tube or tape?
-Carrie
-----Original Message-----
From: Howard Watson [mailto:[log in to unmask]]
Sent: Monday, May 12, 2003 2:17 PM
To: [log in to unmask]
Subject: [TN] Coplanarity of PLCC's
Technetters,
I have been having a problem with a PLCC 68, manufactured by Motorola, where about 1 out of 100 components have 1 corner lead bent upwards creating no solder joint. It's usually pin 9 or 61. I use a DEK 265 Infinity, laser cut 6 mil stencil, and no clean solder paste. The feedback from Motorola is that the lead they measured from one defect was within their coplanarity specification of .004". They suggested using a 7 mil stencil, which I tried with no different result. I also tried increasing the Z distance, to push the component into the paste more, but I don't think there was much of an impact. It seems like it would be very difficult to push this many leads further into the paste. Theoretically, with a 7 mil paste deposit, and if the component went half way down, then I would only have .0035" of allowance for coplanarity, which would not suffice for the tolerance of this component, rig! ht?
My next plan is to overprint the solder paste 20% longer than the pad (.08" x .025"), and use no reduction of the width (I normally use 10% reduction), with the hope that the reflowed solder would "bridge" the gap. I am hoping this will work, but does anyone have another suggestion? Do you think its possible to push the component further into the paste? A step stencil is impossible because of the density, and there is nothing on the PCB with a finer pitch than this component. Thanks in advance for your help.
Howard Watson
SMT Manufacturing Engineer
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