|Ask the Experts
August 12, 2009 - Updated
August 10, 2009 - Originally Posted
Need for SMT adhesives
If double sided surface mount assemblies are the way of the future, should we anticipate a growing or declining need for surface mount adhesives?
|Expert Panel Responses
Double sided boards have been around since the beginning of SMT. In the early days, most SMT lines had a screen printer and a glue dispenser, a chip placer, a flexible placer and a reflow oven.
Most double sided boardsplaced the passive componentson the first pass, often into glue,and sometimes UV cured, then the active side of the board was placedinto solder and reflowed. Through hole parts were then inserted on the active side and the glue side of the board was finished along with the through hole parts in the wave solder.
As solder paste and reflow technology improved, adhesives became less important. Surface tension would hold most small components on the board during reflow even improving placement accuracy in some cases. A slightly higher temperature solder paste could also be used on the bottom side to preventit from going liquid during the second pass.
Today most double sided boards are still placed using solder paste on both sides, however, the push for higher density has forced active components to sometimes be located on both sides of the board. These larger, heaver components on the bottom side of the board has increased the need for adhesives.
A small amount of glue is sometimes necessary to supplement the surface tension on the solder paste and keep the components in place during the second pass through the oven.
So the correct answer to your question is definitely maybe!
It depends largely on what kind of products you assemble. Products that need to be very small, very light weight or very power efficient are more likely to have active components on both sides of the board and will see an increase in the need for adhesive dispensing in the line.
Boards with lots of extra real estate like backplanes and boards that go into refrigerator doors and large cabinets, not so much. I hope this answers your question.
Fuji America Corporation
Scott Wischoffer has been in the SMT industry since 1986 with experience in service, training, sales & applications, and marketing.
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