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AUTOMATIC SOLDER FEEDING PTH DESIGN FOR CLADDED PCB

IP.com Disclosure Number: IPCOM000006760D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2002-Jan-30
Document File: 2 page(s) / 100K

Publishing Venue

Motorola

Related People

Loon Wan Chong: AUTHOR [+2]

Abstract

The latest development in the PCB industry is the introduction of cladded boards. This is a process whereby a PCB, after the normal tin-lead coating on the solder pads, is printed with solder paste on these pads and reflowed without any component on it (hereafter referred as cladding reflow process). As the paste melts and resolidifies, it forms solder bumps on the solder pads which hold a controlled amount of solder on them. This is called a cladded PCB. Subsequently, the cladded PCB will be reflowed with components on it witho& further application of solder paste (hereafter referred as com- ponents reflow process). Cladded PCBs are usully done at the PCB manufacturer's site and hence their custom- ers can immediately use the boards for components reflow process without the need to print solder paste on them.

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MO-LA INC. Technical Developments Volume 18 March 1993

AUTOMATIC SOLDER FEEDING PTH DhIGN

FOR CLADDED PCB I

by Loon Wan Chong and Soo Lit Tan

  The latest development in the PCB industry is the introduction of cladded boards. This is a process whereby a PCB, after the normal tin-lead coating on the solder pads, is printed with solder paste on these pads and reflowed without any component on it (hereafter referred as cladding reflow process). As the paste melts and resolidifies, it forms solder bumps on the solder pads which hold a controlled amount of solder on them. This is called a cladded PCB. Subsequently, the cladded PCB will be reflowed with components on it witho& further application of solder paste (hereafter referred as com- ponents reflow process). Cladded PCBs are usully done at the PCB manufacturer's site and hence their custom- ers can immediately use the boards for components reflow process without the need to print solder paste on them.

  One limitation with this cladding technique is that plated through holes (PTHs) with annular rings can not be cladded. This is because the printed solder paste will flow from the annular rings into the PTHs and clog them up during the cladding reflow process (see Figure 1). Therefore, for PCB where the SMT components solder pads are already cladded, the PTHs for leaded compo- nents require additional printing of solder paste on the annular rings before the components reflow process or these leaded components need to be post soldered after the components reflow process. Another alternative would be the use of solder preform. Either of these alter-

natives is deviating from the cladded PCB's original goals of reducing soldering defects, automating reflow proc- ess and shortening cycle tune and has inevitably intro- duced additional process Variables.

  The following depicts a solution throu...