Screen printing lacquer: mask = diameter of pad mm Photo lacquer : mask = diameter of pad mm Example. 0.15mm

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Annice Rogers
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1 284 Solder Mask 1.0 Application Solder resist is a thermally hardening lacquer applied by screen printing (2-component epoxy resin lacquer) on the board or phototechnically structured after a coating process (foil, liquid film). The tasks of the solder mask are : a.) to avoid short circuits during the soldering process b.) to insulate the compontent parts against the surface of the board c.) to protect the surface of the board against mechanical and chemical influences (corrosion) d.) to improve the electrical parameters of the board (increase of the sparkover (flash-over) voltage) Solder resist may be printed on all common surface-finishes of boards (tin lead, nickel, gold, copper). The standard colour is green. 2.0 Design-rule The data for the solder mask only contain the structures which are intended to be free of lacquer on the board. 2.1 Pads/SMDs The blank spaces for pads and SMD areas in the solder mask must be larger than in the conductive pattern. Screen printing lacquer: mask = diameter of pad mm Photo lacquer : mask = diameter of pad mm Example THT 0.15mm SMD 0.15mm Pad Plated hole Screen print 0.05mm 0.05mm Solder resist Photo lacquer File : Loetstlk.1 Issued : / jvi-wi Revision : --

2 2.2 NPTHs Non-plated holes: see Document Non-Plated Holes [S.217] 2.3 Contours Plated contours and slots must be kept free of solder resist Example 285 Contour of the printed circuit board Solder mask 2.4 PC plugs PC multi- plug connectors must be completely kept free of solder resist Example 2.5 Filled areas Filled areas must have a distance of 0.5 mm to the contour of the board Example PC plug Solder resist 0.5 mm distance Contour of the board Solder resist Plane Area File : Loetstlk.2 Issued : / jvi-wi Revision : --

3 3.0 Note For SMD boards "photo lacquer" should always be specified due to the higher register accuracy. 3.1 DSR The solder mask should be part of the design-rule check in order to ensure that all track connections are covered by lacquer Example Recommended: ø solder mask + 0.1mm ø electrical distance 286 Ø Pad Ø Solder mask Ø Electrical distance Track-width File : Loetstlk.3 Issued : / Wi Revision : --

4 4.0 Photos Solder Mask 287 Solder resist mask over copper-plane surface. Equal cutouts for the pads of circulatory 100 µm. The vias are coated. NPTH (top centred) are correctly kept free of solder stop. Cutouts for the SMD pads of circulatory 60µm for the Fine-Pitch- IC's (the pad-center's distance is 500µm) with a remaining solder mask link of 100µm between neighboured Pads. File : Loetstlk.4 Issued : / Wi Revision : --

5 288 Brown-transparent solder resist above SMD components (standard and finepitch), completely covered vias. The tolerance of the solder mask simulates SMD pads of different lengths in direction of the tracks leading out of the pads. On account of a displacement and oversize of the mask, the absorption of solder and the soldering characteristics of the SMD surface-finishes may be influenced. File : Loetstlk.5 Issued : / Wi

6 289 Via covered by solder resist (right) and open via (left). Micro section of a track completely covered by solder resist at the edges and from the top as a cross section. The lacquer thickness is approx µm in the track-centre and approx. 7-8µm at the edges (in case of cast lacquer). File : Loetstlk.6 Issued : / Wi

7 290 Solder mask with too large dimensions (120µm circularity) for a finepitch component (0.635mm pin distance). The links of the mask are breaking and may have negative effects on the soldering result. File : Loetstlk.7 Issued : / Wi

8 291 Keep-free-areas within the solder mask. Owing to the additional galvanotechnical build up, the cross section of the tracks is increased and therefore also the loading capacity. File : Loetstlk.8 Issued : / Wi

9 Cross references (hyperlinks) Fully automatic casting machine for photo lacquer. In the foreground, the inlet zone; in the centre, the casting curtain for covering the printed circuit board by (here: green) lacquer; in the background, the lacquer dryer. (Manufacturer: Systronic). Solder Mask (comment) [S.331] ; Screen Printing [S.272] ; Non-Plated Holes [S.217] File : Loetstlk.9 Issued : / Wi

How to Build a Printed Circuit Board. Advanced Circuits Inc 2004

How to Build a Printed Circuit Board 1 This presentation is a work in progress. As methods and processes change it will be updated accordingly. It is intended only as an introduction to the production