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HANDS-ON DESIGN TIPS

Gert Baars

When soldering SMDs (surfacemount devices) onto a circuitboard, it is often difficult to keepthe tiny component correctly posi-tioned. With two hands in use,one holding the soldering ironand the other, the solder tin, you

really need a third hand to keepthe SMD in place. Fair enough,SMDs with a lead pitch of 0.05inch stand a good chance of suc-cess if you melt-and-move a littleto first secure the two corner pinsof the IC to make sure it’s prop-erly aligned on the solder pads.Smaller ICs with a lead pitch of just 0.65 mm or even 0.5 mm

are far more difficult to handleand really suitable for machinemounting only. A possible solutionto the problem is to secure the ICto the board with a drop of hobby glue. Next, you align theIC using a magnifying glass andallow the glue to set. This maylast up to a couple of hours.The author having run into this

problem often enough, an ideacame to mind to make a simplebut effective little tool that’s easyto produce at home.We’re looking at a kind of minia-ture clamping device capable of holding an SMD in place with suf-ficient force to allow it to be sol-dered, but less pressure than tocrush the device! The first version

consists of three strips of PCBmaterial, an M3 nut, a pressurespring and some washers and

nuts. The drawing shows that A,B and C are pieces of unetchedboard material secured to form aU-shape. At point ‘A’, a 3-mm

hole is drilled at the end. A 60-mm long M3 bolt with one endfiled into a tip is inserted into thishole. The bolt end protrudingfrom the upper board strip (A)takes an M3 washer and aspring. The spring is conveniently

SMD soldering aid

salvaged from a ballpoint penand should have relatively lowpressure tension. Next, the longM3 bolt takes a washer and a

nut, causing the spring to pushthe screw downwards. With a lit-tle adjustment of the nut, a settingcan be found at which the screwexerts a little pressure on the ICon the board underneath it — justenough for our purpose. The

drawing really speaks for itself.The tool is simple to use — first,put the SMD roughly in positionon the board and lift the bolt a lit-tle. This is easiest done by push-ing up the tip side. Slide theboard under the bolt, aligning theIC under the tip. Because the boltwill have some play, the IC canbe moved exactly onto its foot-

print using the tweezers, a match-stick or a small screwdriver. Allthe while, the bolt will exertenough pressure on the IC toenable you to solder the cornerpins without shifting the SMD, butalso allowing enough play tomove the IC about a little whilealigning.Should the IC start to slide off in

the wrong direction, the springpressure has to be increased a lit-tle by turning the nut up a little.The sizes of the materials usedmay be selected to personalrequirements. The author’s firstversion of the tool is intended forsmaller PCBs and has the follow-ing dimensions:

A = 15×60×2 mm;B = 15×45×2 mm andC = 15×75×2 mm.

In principle, it is also possible tomachine the U piece from a sin-gle piece of metal sheet by bend-ing two right angles and a curva-ture. If the material used is neithertoo thick or too short, it will

exhibit enough tension of its ownso a spring will not be required.(050277-1)

050277 - 12

M3 bolt

curved aluminium sheet

solder

SMD on PCBSMD

M3 nut

M3 nut

solder

M3 x 60 bolt

M3 washer

M3 nut

ballpoint spring

solder solder

SMD on PCB

050277 - 11

SMD